Showing papers in "Development in 1995"
TL;DR: It appears that Fgf8 is structurally the most complex member of the FGF family described to date, with at least seven transcripts encoding a family of secreted FGF8 proteins with different N termini.
Abstract: Evidence is accumulating that members of the FGF gene family provide signals that act locally to regulate growth and patterning in vertebrate embryos. In this report, we provide a detailed analysis of the mouse Fgf8 gene. We have mapped the Fgf8 locus to the distal region of mouse chromosome 19, and sequenced the 5' coding region of the gene. Our data identify a new coding exon, and locate multiple splice donor and splice acceptor sites that can be used to produce at least seven transcripts encoding a family of secreted FGF8 proteins with different N termini. From these results, it appears that Fgf8 is structurally the most complex member of the FGF family described to date. In the embryo, many of the regions in which Fgf8 RNA is localized are known to direct outgrowth and patterning, including the apical ectodermal ridge of the limb bud, the primitive streak and tail bud, the surface ectoderm overlying the facial primorida and the midbrain-hindbrain junction, suggesting that FGF8 may be a component of the regulatory signals that emanate from these regions.
1,222 citations
TL;DR: The data indicate that the primary effect of loss of TGF beta 1 function in vivo is not increased haematopoietic or endothelial cell proliferation, which might have been expected by deletion of a negative growth regulator, but defective haem atopoiesis and endothelial differentiation.
Abstract: Transforming growth factor beta 1 (TGF beta 1) is shown here to be required for yolk sac haematopoiesis and endothelial differentiation. Mice with a targeted mutation in the TGF beta 1 gene were examined to determine the cause of prenatal lethality, which occurs in 50% of homozygous TGF beta 1 null (TGF beta 1-/-) conceptions. 50% of TGF beta 1-/- and 25% of TGF beta 1-+-) conceptions. 50% of TGF beta 1-/- and 25% of TGF beta 1+/- conceptuses were found to die at around 10.5 dpc. The primary defects were restricted to extraembryonic tissues, namely the yolk sac vasculature and haematopoietic system. The embryos per se showed developmental retardation, oedema and necrosis, which were probably secondary to the extraembryonic lesions. The defect in vasculogenesis appeared to affect endothelial differentiation, rather than the initial appearance and outgrowth of endothelial cells. Initial differentiation of yolk sac mesoderm to endothelial cells occurred, but defective differentiation resulted in inadequate capillary tube formation, and weak vessels with reduced cellular adhesiveness. Defective haematopoiesis resulted in a reduced erythroid cell number within the yolk sac. Defective yolk sac vasculogenesis and haematopoiesis were present either together, or in isolation of each other. The phenotypes are consistent with the observation of abundant TGF beta 1 gene expression in both endothelial and haematopoietic precursors. The data indicate that the primary effect of loss of TGF beta 1 function in vivo is not increased haematopoietic or endothelial cell proliferation, which might have been expected by deletion of a negative growth regulator, but defective haematopoiesis and endothelial differentiation.
1,060 citations
TL;DR: Observational studies suggest strongly that both endocrine and exocrine cells arise from the same endodermal rudiment, and it seems likely that there is a continuous slow turnover of cells, fed from a stem cells population in the ducts, and that the controls on the production rate are local rather than systemic.
Abstract: The pancreas is an organ containing two distinct populations of cells, the exocrine cells that secrete enzymes into the digestive tract, and the endocrine cells that secrete hormones into the bloodstream. It arises from the endoderm as a dorsal and a ventral bud which fuse together to form the single organ. Mammals, birds, reptiles and amphibians have a pancreas with similar histology and mode of development, while in some fish, the islet cells are segregated as Brockmann bodies. Invertebrates do not have a pancreas, but comparable endocrine cells may be found in the gut or the brain. The early pancreatic bud shows uniform expression of the homeobox gene IPF-1 (also known as IDX-1, STF-1 or PDX), which when mutated to inactivity leads to total absence of the organ. The occurrence of heterotopic pancreas in the embryo, and also the metaplasias that can be displayed by a regenerating pancreas in the adult, both suggest that only a few gene products distinguish the pancreatic cell state from that of the surrounding tissues of duodenum, gall bladder and liver. In the developing pancreatic buds, the endocrine cells start to differentiate before the exocrine cells, and co-expression of different hormones by the same cell is often observed at early stages. Although pancreatic endocrine cells produce many gene products also characteristic of neurons, evidence from in vitro cultures and from quailchick grafts shows that they are of endogenous and not of neural crest origin. Observational studies suggest strongly that both endocrine and exocrine cells arise from the same endodermal rudiment. Development of the pancreas in embryonic life requires a trophic stimulus from the associated mesenchyme. In postnatal life, all cell types in the pancreas continue to grow. Destruction of acinar tissue by duct ligation or ethionine treatment is followed by rapid regeneration. Surgical removal of parts of the pancreas is followed by moderate but incomplete regeneration of both acini and islets. Poisoning with alloxan or streptozotocin can lead to permanent depletion of beta cells. Although the cell kinetics of the pancreas are not understood, it seems likely that there is a continuous slow turnover of cells, fed from a stem cells population in the ducts, and that the controls on the production rate of each cell type are local rather than systemic.
1,007 citations
TL;DR: Caput epididymal sperm, which lack the ability to undergo capacitation in vitro, do not display this capacitation-dependent subset of tyrosine phosphorylated proteins in complete media even after extended incubation periods, and do not fertilize metaphase II-arrested eggs in vitro.
Abstract: The molecular basis of mammalian sperm capacitation, defined functionally as those processes that confer on the sperm the acquisition of fertilization-competence either in vivo in the female reproductive tract or in vitro, is poorly understood. We demonstrate here that capacitation of caudal epididymal mouse sperm in vitro is accompanied by a time-dependent increase in the protein tyrosine phosphorylation of a subset of proteins of M(r) 40,000-120,000. Incubation of sperm in media devoid of bovine serum albumin, CaCl2 or NaHCO3, components which individually are required for capacitation, prevent the sperm from undergoing capacitation as assessed by the ability of the cells to acquire the pattern B chlortetracycline fluorescence, to undergo the zona pellucida-induced acrosome reaction and, in some cases, to fertilize metaphase II-arrested eggs in vitro. In each of these cases the protein tyrosine phosphorylation of the subset of capacitation-associated proteins does not occur. Protein tyrosine phosphorylation of these particular proteins, as well as sperm capacitation, can be recovered in media devoid of each of these three constituents (bovine serum albumin, CaCl2 or NaHCO3) by adding back the appropriate component in a concentration-dependent manner. The requirement of NaHCO3 for these phosphorylations is not due to an alkalinization of intracellular sperm pH or to an increase in media pH. Caput epididymal sperm, which lack the ability to undergo capacitation in vitro, do not display this capacitation-dependent subset of tyrosine phosphorylated proteins in complete media even after extended incubation periods, and do not fertilize metaphase II-arrested eggs in vitro.(ABSTRACT TRUNCATED AT 250 WORDS)
948 citations
TL;DR: It is proposed that Notch1 normally coordinates the process of somitogenesis, and a model of how this might occur is provided, and it is found that som itogenesis is delayed and disorganized in Notch 1 mutant embryos.
Abstract: Members of the Notch family of transmembrane receptors mediate a number of developmental decisions in invertebrates. In order to study Notch function in a vertebrate organism, we have mutated the Notch1 gene of the mouse. Notch1 gene function is required for embryonic survival in the second half of gestation. In the first half of gestation, we have found no effect of the mutation on the normal programs of neurogenesis, myogenesis or apoptosis. We conclude that Notch1 function is not essential for these processes, at least in early postimplantation development. However, we have found that somitogenesis is delayed and disorganized in Notch1 mutant embryos. We propose that Notch1 normally coordinates the process of somitogenesis, and we provide a model of how this might occur.
895 citations
TL;DR: Pax-2 mouse mutants provide an animal model for human hereditary kidney diseases and data show that Pax-2 is required for multiple steps during the differentiation of intermediate mesoderm.
Abstract: Urogenital system development in mammals requires the coordinated differentiation of two distinct tissues, the ductal epithelium and the nephrogenic mesenchyme, both derived from the intermediate mesoderm of the early embryo. The former give rise to the genital tracts, ureters and kidney collecting duct system, whereas mesenchymal components undergo epithelial transformation to form nephrons in both the mesonephric (embryonic) and metanephric (definitive) kidney. Pax-2 is a transcriptional regulator of the paired-box family and is widely expressed during the development of both ductal and mesenchymal components of the urogenital system. We report here that Pax-2 homozygous mutant newborn mice lack kidneys, ureters and genital tracts. We attribute these defects to dysgenesis of both ductal and mesenchymal components of the developing urogenital system. The Wolffian and Mullerian ducts, precursors of male and female genital tracts, respectively, develop only partially and degenerate during embryogenesis. The ureters, inducers of the metanephros are absent and therefore kidney development does not take place. Mesenchyme of the nephrogenic cord fails to undergo epithelial transformation and is not able to form tubules in the mesonephros. In addition, we show that the expression of specific markers for each of these components is de-regulated in Pax-2 mutants. These data show that Pax-2 is required for multiple steps during the differentiation of intermediate mesoderm. In addition, Pax-2 mouse mutants provide an animal model for human hereditary kidney diseases.
860 citations
TL;DR: A comparative study of the developmental patterns of homeobox gene expression and developmental morphology between animals that have homologous regulatory genes but different morphologies, which contributes a mechanistic level to the assumed homology of these regions in vertebrates.
Abstract: Hoxgenes are a family of regulatory genes expressed along the A-P axis in most metazoans. Because homeobox genes encode transcription regulators active in pattern formation during ontogeny, they are obvious factors to study in the investigation of the mechanistic basis for ontogeny, as well as in the relationship between ontogeny and phylogeny. This paper presents a comparative study of the developmental patterns of homeobox gene expression and morphogenesis along the A-P axis between related animals that have homologous regulatory genes but different axial morphologies. The participation of different numbers of segments in any given region of the vertebrate body and the different positions of the appendages relative to the A-P axis, have provoked comment and theory from morphologists for centuries. While common generative rules govern mesodermal segments within individual organisms (serial homology), and common ancestry accounts for their presence in all chordates (historical homology), details of this segmental organization differ dramatically between related organisms resulting in a variety of axial formulae, defined here as the number of vertebrae of each morphological type, e.g. cervical, thoracic, lumbar, etc. In 1906, E. S. Goodrich proposed the term ‘transposition’ to describe evolutionary changes in the number of segments included in any vertebral region. Goodrich surmised that serially and historically homologous regions behave as pliable elements that can slide up or down the A-P axis during evolution. Lankester (1910) expanded the description with a useful musical analogy, comparing an axial structure or region to a tune that can be transposed up or down the scale. The pattern of variation and constraint in axial formulae among different classes of vertebrates demonstrates that transposition has been an important evolutionary phenomenon in the establishment and radiation of different vertebrate groups (Gadow, 1933; Carroll, 1988). Mammals are a vertebrate class with extreme morphological variation. With very few exceptions however, they are constrained by the fixed number of seven cervical vertebrae whether they be whales or giraffes. Birds are not constrained in this character, and vary from 13 (pigeons and swifts), to 25 (swans) cervical vertebrae. Extremes among the vertebrates include the Cretaceous plesiosaur, Elasmosaurussp. which had as many as 76 cervical vertebrae; snakes, with as many as 350 individual vertebrae of equivocal types; and the modern anurans (frogs) with never more than 9 and as few as 6 total presacral vertebrae. Even when the total number of pre-caudal vertebrae is almost the same, as is the case between chickens and mice, the relative length of specific regions, such as cervical versus thoracic, can vary considerably. Members of the Hoxfamily of homeobox genes are expressed along the A-P axis at specific levels in the central
812 citations
TL;DR: The results raise the possibility of abortifacients targeting alpha 4 integrins, and raise serious questions about potential side effects of drugs currently being designed to blockalpha 4 integrin functions in inflammation.
Abstract: alpha 4 integrins are cell surface receptors that mediate cell-extracellular matrix (ECM) and cell-cell adhesions by interacting with fibronectin (FN) and vascular cell adhesion molecule 1 (VCAM-1), respectively. We have generated a null mutation in the gene for the alpha 4 integrin subunit. Homozygous null embryos express no alpha 4 integrins and show two unexpected defects, both of which lead to embryonic lethality. The first defect is failure of fusion of the allantois with the chorion during placentation. The second is in the development of the epicardium and coronary vessels leading to cardiac hemorrhage. Both processes clearly involve alpha 4 integrin interactions that were previously unsuspected. alpha 4 integrin and VCAM-1 are expressed at the sites of these interactions. These results raise the possibility of abortifacients targeting alpha 4 integrins, and raise serious questions about potential side effects of drugs currently being designed to block alpha 4 integrin functions in inflammation.
809 citations
TL;DR: Up-regulation of protein tyrosine phosphorylation by cAMP/PKA in sperm is, to the authors' knowledge, the first demonstration of such an interrelationship between tyrosin kinase/phosphatase and PKA signaling pathways.
Abstract: In the accompanying report (Visconti, P.E., Bailey, J.L., Moore, G.D., Pan, D., Olds-Clarke, P. and Kopf, G.S. (1995) Development, 121, 1129–1137) we demonstrated that the tyrosine phosphorylation of a subset of mouse sperm proteins of M(r) 40,000-120,000 was correlated with the capacitation state of the sperm. The mechanism by which protein tyrosine phosphorylation is regulated in sperm during this process is the subject of this report. Cauda epididymal sperm, when incubated in media devoid of NaHCO3, CaCl2 or bovine serum albumin do not display the capacitation-associated increases in protein tyrosine phosphorylation of this subset of proteins. This NaHCO3, CaCl2 or bovine serum albumin requirement for protein tyrosine phosphorylation can be completely overcome by the addition of biologically active, but not inactive, cAMP analogues. Addition of the active cAMP analogues to sperm incubated in media devoid of NaHCO3, CaCl2 or bovine serum albumin overcomes the inability of these media to support capacitation, as assessed by the ability of the cells to acquire the pattern B chlortetracycline fluorescence, to undergo the zona pellucida-induced acrosome reaction and, in some cases, to fertilize metaphase II-arrested eggs in vitro. The effects of the cAMP analogues to enhance protein tyrosine phosphorylation and to promote capacitation appears to be at the level of the cAMP-dependent protein kinase (PKA), since two specific inhibitors of this enzyme (H-89 and Rp-cAMPS) block the capacitation-dependent increases in protein tyrosine phosphorylation in sperm incubated in media supporting capacitation. Capacitation, as assessed by the aforementioned endpoints, also appears to be inhibited by H-89 in a concentration-dependent manner. These results provide further evidence for the interrelationship between protein tyrosine phosphorylation and the appearance of the capacitated state in mouse sperm. They also demonstrate that both protein tyrosine phosphorylation and capacitation appear to be regulated by cAMP/PKA. Up-regulation of protein tyrosine phosphorylation by cAMP/PKA in sperm is, to our knowledge, the first demonstration of such an interrelationship between tyrosine kinase/phosphatase and PKA signaling pathways.
801 citations
TL;DR: One of the identified genes, lats, has been cloned and encodes a putative protein kinase that shares high levels of sequence similarity with three proteins in budding yeast and Neurospora that are involved in regulation of the cell cycle and growth.
Abstract: We have identified recessive overproliferation mutations by screening and examining clones of mutant cells in genetic mosaics of the fruitfly Drosophila melanogaster. This type of screen provides a powerful approach for identifying and studying potential tumor suppressors. One of the identified genes, lats, has been cloned and encodes a putative protein kinase that shares high levels of sequence similarity with three proteins in budding yeast and Neurospora that are involved in regulation of the cell cycle and growth. Mutations in lats cause dramatic overproliferation phenotypes and various developmental defects in both mosaic animals and homozygous mutants.
784 citations
TL;DR: It is demonstrated that, although beta-catenin is expressed rather ubiquitously, it is specifically required in the ectodermal cell layer, as it binds to the cytoplasmic domain of E-cadherin and to alpha-Catenin.
Abstract: Molecular analysis of the cadherin-catenin complex elucidated the central role of beta-catenin in this adhesion complex, as it binds to the cytoplasmic domain of E-cadherin and to alpha-catenin. beta-Catenin may also function in signalling pathways, given its homology to the gene product of the Drosophila segment polarity gene armadillo, which is known to be involved in the wingless signalling cascade. To study the function of beta-catenin during mouse development, gene knock-out experiments were performed in embryonic stem cells and transgenic mice were generated. beta-Catenin null-mutant embryos formed blastocysts, implanted and developed into egg-cylinder-stage embryos. At day 7 post coitum, the development of the embryonic ectoderm was affected in mutant embryos. Cells detached from the ectodermal cell layer and were dispersed into the proamniotic cavity. No mesoderm formation was observed in mutant embryos. The development of extraembryonic structures appeared less dramatically or not at all affected. Our results demonstrate that, although beta-catenin is expressed rather ubiquitously, it is specifically required in the ectodermal cell layer.
TL;DR: It is proposed that CLV1 and CLV3 are required to promote the differentiation of cells at the shoot and floral meristem.
Abstract: throughout flower development. clv3 root meristems are unaffected, indicating that CLV3 is a specific regulator of shoot and floral meristem development. We demonstrate that the strong clv3-2 mutant is largely epistatic to clv1 mutants, and that the semi-dominance of clv1 alleles is enhanced by double heterozygosity with clv3 alleles, suggesting that these genes work in the same pathway to control meristem development. We propose that CLV1 and CLV3 are required to promote the differentiation of cells at the shoot and floral meristem. SUMMARY
TL;DR: It is suggested that Otx2 expression in endomesoderm and ectoderm is required for anterior neuroectoderm specification, and in gastrulating heterozygous embryos, a post-transcriptional repression acts on lacZ transcripts in the ectodermal layer, but not in the external layer, suggesting that different post- transcriptional mechanisms control Otx1 expression in both layers.
Abstract: We have replaced part of the mouse homeogene Otx2 coding region with the E. coli lacZ coding sequence, thus creating a null allele of Otx2. By 9.5 dpc, homozygous mutant embryos are characterized by the absence of forebrain and midbrain regions. From the early to midstreak stages, endomesodermal cells expressing lacZ fail to be properly localized anteriorly. In the ectodermal layer, lacZ transcription is progressively extinguished, being barely detectable by the late streak stage. These data suggest that Otx2 expression in endomesoderm and ectoderm is required for anterior neuroectoderm specification. In gastrulating heterozygous embryos, a post-transcriptional repression acts on lacZ transcripts in the ectoderm, but not in the external layer, suggesting that different post-transcriptional mechanisms control Otx2 expression in both layers.
TL;DR: The isolation of a sequence-related gene referred to as Six3 is reported, which is one of the most anterior homeobox gene reported to date and supports the idea that mammals and insects share control genes such as eyeless/Pax6 and also possibly other members of the regulatory cascade required for eye morphogenesis.
Abstract: The Drosophila sine oculis homeobox-containing gene is known to play an essential role in controlling the initial events of pattern formation in the eye disc and is also required for the development of other parts of the fly visual system including the optic lobes. In this paper, we report the isolation of a sequence-related gene referred to as Six3. Based on its amino acid sequence, this gene can be included in the new Six/sine oculis subclass of homeobox genes. Early on, Six3 expression is restricted to the anterior neural plate including areas that later will give rise to ectodermal and neural derivatives. Later, once the longitudinal axis of the brain bends, Six3 mRNA is also found in structures derived from the anterior neural plate: ectoderm of nasal cavity, olfactory placode and Rathke9s pouch, and also the ventral forebrain including the region of the optic recess, hypothalamus and optic vesicles. Based on this expression pattern, we conclude that Six3 is one of the most anterior homeobox gene reported to date. The high sequence similarity of Six3 with the Drosophila sine oculis, and its expression during eye development, suggests that this gene is the likely murine homologue. This finding supports the idea that mammals and insects share control genes such as eyeless/Pax6 (Halder, G., Callaerts, P. and Gehring, W. J. (1995) Science 267, 1788–1792), and also possibly other members of the regulatory cascade required for eye morphogenesis. In Small eye (Pax6) mouse mutants Six3 expression is not affected. Finally, based on the chromosomal localization and the expression pattern of the mouse Six3 gene, the human Six3 cognate could be a good candidate to be at least one of the genes affected in patients with holoprosencephaly type 2 due to an interstitial deletion of 2p21-p22. This region shares a homology with the distal region of mouse chromosome 17 where Six3 has been mapped.
TL;DR: Analysis of patterns of programmed cell death and absence of nasal region expression from an Msx-1 transgene in Sey/Sey embryos suggest a requirement for Pax-6 in the transition from presumptive nasal ectoderm to placode, and that Msx -1, or genes regulating it, are possible targets for Pax -6.
Abstract: Small eye (Sey) mice homozygous for mutations in the Pax-6 gene have no lenses and no nasal cavities. We have examined the ontogeny of eye and nasal defects in Sey/Sey embryos and have related the defects seen to the pattern of Pax-6 mRNA expression in the mouse during normal eye and nasal development. There are two principal components of the early eye, the neural ectoderm of the optic vesicle, which forms the retina, and the overlying surface ectoderm, which forms the lens and cornea. By studying these interacting tissues in normal and Sey/Sey embryos, we have identified processes for which Pax-6 is important and can thus suggest possible roles for the Pax-6 gene. Pax-6 is essential for the formation of lens placodes from surface ectoderm. In normal development, early Pax-6 mRNA expression in a broad domain of surface ectoderm is downregulated, but expression is specifically maintained in the developing lens placode. Moreover, other Pax-6-expressing tissues are frequently those that have can transdifferentiate into lens. Thus, phenotype and expression together suggest a role for Pax-6 in lens determination. At least some functions of Pax-6 can be separated from the influence of other tissues. Early Sey/Sey optic vesicles are abnormally broad and fail to constrict proximally. These defects occur prior to the time of lens placode formation and probably reflect a requirement for Pax-6 in neural ectoderm. In surface ectoderm domains, where Pax-6 expression is known to be independent of the presence of an optic vesicle, Pax-6 function is required for the maintenance of its own transcription. The mutual dependency of lens and optic vesicle development can also be studied using the Small eye mutation. Using region-specific markers we find that, in the morphologically abnormal Sey/Sey optic vesicles, aspects of normal proximo-distal specification nevertheless persist, despite the complete absence of lens. Like the lens, the nasal cavities develop from ectodermal placodes that normally express Pax-6 mRNA, fail to form in Sey/Sey mice and show Pax-6-dependent Pax-6 mRNA regulation. Analysis of patterns of programmed cell death and absence of nasal region expression from an Msx-1 transgene in Sey/Sey embryos suggest a requirement for Pax-6 in the transition from presumptive nasal ectoderm to placode, and that Msx-1, or genes regulating it, are possible targets for Pax-6.
TL;DR: In this paper, the authors describe studies of the expression of several genes in the mouse between 7.5 and 10.5 days post coitum (dpc) that provide evidence for the trajectory of the anterior-posterior axis and the longitudinal organization of the CNS, and demonstrate that the earliest longitudinal axon pathways of the forebrain are spatially correlated with the longitudinal domain defined by Nkx-2.2.
Abstract: Over the last century, several morphological models of forebrain organization have been proposed that hypothesize alternative topological solutions for the relationships of the histogenic primordia. Central to all of these models are their definitions of the longitudinal axis and the longitudinal organization of the neural plate and neural tube. To understand the longitudinal organization of the anterior brain, we have sought to identify molecular properties that are continuous along the entire longitudinal axis of the embryonic CNS. In this essay, we describe studies of the expression of several genes in the mouse between 7.5 (presomite stage) and 10.5 days post coitum (dpc) that provide evidence for the trajectory of the anterior-posterior axis and the longitudinal organization of the anterior CNS. Specifically, we report that the expression of noggin, sonic hedgehog and Nkx-2.2 define longitudinal columns of cells that are present along the entire CNS axis. Within the forebrain, the expression of these genes, as well as that of Nkx-2.1 and BF-1, are in distinct longitudinal regions in the neural plate and tube. We demonstrate that the earliest longitudinal axon pathways of the forebrain are spatially correlated with the longitudinal domain defined by Nkx-2.2. Finally, expression of the former genes, and Otx-1 and Emx-2, suggests that the cephalic neural plate is organized into molecularly distinct domains delimited by longitudinal and transverse borders; these results provide a foundation for defining the mechanisms that pattern the neural plate.
TL;DR: This work uses RNase protection to map the extent of the less abundant Sry transcript in the developing gonad and demonstrates that it is a linear mRNA derived from a single exon, which defines the critical period during which Sry must act to initiate Sertoli cell differentiation.
Abstract: In the mouse, Sry is expressed by germ cells in the adult testis and by somatic cells in the genital ridge. Transcripts in the former exist as circular RNA molecules of 1.23 kb, which are unlikely to be efficiently translated. We have used RNase protection to map the extent of the less abundant Sry transcript in the developing gonad. We demonstrate that it is a linear mRNA derived from a single exon. This begins in the unique region 5′ of the protein coding region and extends several kilobases into the 3′ arm of the large inverted repeat which bounds the Sry genomic locus. Knowledge of this transcript, which is very different from that of the human SRY gene, allows us to predict its protein product and reveals several features which may be involved in translational control. Our data is also consistent with there being two promoters for the Sry gene, a proximal one that gives functional transcripts in the genital ridge and a distal promoter used in germ cells in the adult testis. As RNase protection is a quantitative technique, a detailed timecourse of Sry expression was carried out using accurately staged samples. Sry transcripts are first detectable just after 10.5 days post coitum, they reach a peak at 11.5 days and then decline sharply so that none are detected 24 hours later. This was compared with anti-Mullerian hormone gene expression, an early marker of Sertoli cells and the first known downstream gene of Sry. Amh expression begins 20 hours after the onset of Sry expression at a time when Sry transcripts are at their peak. While this result does not prove a direct interaction between the two genes, it defines the critical period during which Sry must act to initiate Sertoli cell differentiation.
TL;DR: The low-affinity receptor for leukemia inhibitory factor (LIFR) interacts with gp130 to induce an intracellular signal cascade, which leads to poor intrauterine nutrition but allows fetuses to continue to term.
Abstract: The low-affinity receptor for leukemia inhibitory factor (LIFR) interacts with gp130 to induce an intracellular signal cascade. The LIFR-gp130 heterodimer is implicated in the function of diverse systems. Normal placentation is disrupted in LIFR mutant animals, which leads to poor intrauterine nutrition but allows fetuses to continue to term. Fetal bone volume is reduced greater than three-fold and the number of osteoclasts is increased six-fold, resulting in severe osteopenia of perinatal bone. Astrocyte numbers are reduced in the spinal cord and brain stem. Late gestation fetal livers contain relatively high stores of glycogen, indicating a metabolic disorder. Hematologic and primordial germ cell compartments appear normal. Pleiotropic defects in the mutant animals preclude survival beyond the day of birth.
TL;DR: In mouse, STF-1 not only labels a domain of intestinal epithelial cells but also provides a spatial and temporal marker of endodermal commitment to a pancreatic and subsequently, to an endocrine beta cell fate.
Abstract: The XlHbox 8 homeodomain protein of Xenopus and STF-1, its mammalian homolog, are selectively expressed by beta cells of adult mouse pancreatic islets, where they are likely to regulate insulin expression. We sought to determine whether the expression of the homeobox protein/s during mouse embryonic development was specific to beta cells or, alternatively, whether XlHbox 8/STF-1 protein/s were initially expressed by multipotential precursors and only later became restricted to the insulin-containing cells. With two antibodies, we studied the localization of STF-1 during murine pancreatic development. In embryos, as in adults, STF-1 was expressed by most beta cells, by subsets of the other islet cell types and by mucosal epithelial cells of the duodenum. In addition, most epithelial cells of the pancreatic duct and exocrine cells of the pancreas transiently contained STF-1. We conclude that in mouse, STF-1 not only labels a domain of intestinal epithelial cells but also provides a spatial and temporal marker of endodermal commitment to a pancreatic and subsequently, to an endocrine beta cell fate. We propose a model of pancreatic cell development that suggests that exocrine and endocrine (alpha, beta, delta and PP) cells arise from a common precursor pool of STF-1+ cells and that progression towards a defined monospecific non-beta cell type is correlated with loss of STF-1 expression.
TL;DR: Using virally mediated misexpression, it is shown that Sonic hedgehog is sufficient to induce ectopic expression of Bmp-4 and specific Hoxd genes within the mesoderm, which appears to act as a signal in an epithelial-mesenchymal interaction in the earliest stages of chick hindgut formation.
Abstract: Reciprocal inductive signals between the endoderm and mesoderm are critical to vertebrate gut development. Sonic hedgehog encodes a secreted protein known to act as an inductive signal in several regions of the developing embryo. In this report, we provide evidence to support the role of Sonic hedgehog and its target genes Bmp-4 and the Abd-B-related Hox genes in the induction and patterning the chick hindgut. Sonic is expressed in the definitive endoderm at the earliest stage of chick gut formation. Immediately subjacent to Sonic expression in the caudal endoderm is undifferentiated mesoderm, later to become the visceral mesoderm of the hindgut. Genes expressed within this tissue include Bmp-4 (a TGF-beta relative implicated in proper growth of visceral mesoderm) and members of the Abd-B class of Hox genes (known regulators of pattern in many aspects of development). Using virally mediated misexpression, we show that Sonic hedgehog is sufficient to induce ectopic expression of Bmp-4 and specific Hoxd genes within the mesoderm. Sonic therefore appears to act as a signal in an epithelial-mesenchymal interaction in the earliest stages of chick hindgut formation. Gut pattern is evidenced later in gut morphogenesis with the presence of anatomic boundaries reflecting phenotypically and physiologically distinct regions. The expression pattern of the Abd-b-like Hox genes remains restricted in the hindgut and these Hox expression domains reflect gut morphologic boundaries. This finding strongly supports a role for these genes in determining the adult gut phenotype. Our results provide the basis for a model to describe molecular controls of early vertebrate hindgut development and patterning. Expression of homologous genes in Drosophila suggest that aspects of gut morphogenesis may be regulated by similar inductive networks in the two organisms.
TL;DR: Results show that cloche is involved in the genesis and early diversification of the endothelial and blood lineages, possibly by affecting a common progenitor cell population.
Abstract: Endothelial and hematopoietic cells appear synchronously on the extra-embryonic membranes of amniotes in structures known as blood islands. This observation has led to the suggestion that these two ventral lineages share a common progenitor. Recently, we have shown in the zebrafish, Danio rerio, that a single cell in the ventral marginal zone of the early blastula can give rise to both endothelial and blood cells as well as to other mesodermal cells (Stainier, D. Y. R., Lee, R. K. and Fishman, M. C. (1993). Development 119, 31–40; Lee, R. K. K., Stainier, D. Y. R., Weinstein, B. M. and Fishman, M. C. (1994). Development 120, 3361–3366). Here we describe a zebrafish mutation, cloche, that affects both the endothelial and hematopoietic lineages at a very early stage. The endocardium, the endothelial lining of the heart, is missing in mutant embryos. This deletion is selective as evidenced by the presence of other endothelial cells, for example those lining the main vessels of the trunk. Early cardiac morphogenesis proceeds normally even in the absence of the endocardium. The myocardial cells form a tube that is demarcated into chambers, beats rhythmically, but exhibits a reduced contractility. This functional deficit is likely due to the absence of the endocardial cells, although it may be a direct effect of the mutation on the myocardial cells. Cell transplantation studies reveal that the endothelial defect, i.e. the endocardial deletion, is a cell-autonomous lesion, consistent with the possibility that cloche is part of a signal transduction pathway. In addition, the number of blood cells is greatly reduced in cloche mutants and the hematopoietic tissues show no expression of GATA-1 or GATA-2, two key hematopoietic transcription factors that are first expressed during early embryogenesis. These results show that cloche is involved in the genesis and early diversification of the endothelial and blood lineages, possibly by affecting a common progenitor cell population.
TL;DR: Important roles for VCAM-1 and alpha 4 in the development of the placenta and the heart are suggested, as well as a reciprocal fashion in the chorion and allantois and in the epicardium and the underlying myocardium.
Abstract: VCAM-1 is a cytokine-inducible cell surface protein capable of mediating adhesion to leukocytes expressing alpha 4 integrins. Mice deficient in VCAM-1 expression were produced by targeted homologous recombination in ES cells. VCAM-1-deficient embryos were not viable and exhibited either of two distinct phenotypes. Approximately half of the embryos died before embryonic day 11.5 and exhibited a severe defect in placental development in which the allantois failed to fuse with the chorion. The remaining VCAM-1-deficient embryos survived to embryonic day 11.5-12.5 and displayed several abnormalities in their developing hearts including a reduction of the compact layer of the ventricular myocardium and intraventricular septum. The hearts also contained significant amounts of blood in the pericardial space and lacked an epicardium. alpha 4 and VCAM-1 were found to be expressed in wild-type embryos in a reciprocal fashion in the chorion and allantois and in the epicardium and the underlying myocardium, although VCAM-1 was expressed in the intraventricular septum in the absence of adjacent alpha 4-expressing cells. These data suggest important roles for VCAM-1 and alpha 4 in the development of the placenta and the heart.
TL;DR: It is demonstrated that en governs growth and patterning in both compartments by controlling the expression of the secreted proteins hedgehog and decapentaplegic as well as the response of cells to these signaling molecules, and evidence suggesting that dpp may exert its organizing influence by acting as a gradient morphogen in contrast to hh which appears to act principally as a short range inducer of dpp.
Abstract: The Drosophila wing is formed by two cell populations, the anterior and posterior compartments, which are distinguished by the activity of the selector gene engrailed (en) in posterior cells. Here, we show that en governs growth and patterning in both compartments by controlling the expression of the secreted proteins hedgehog (hh) and decapentaplegic (dpp) as well as the response of cells to these signaling molecules. First, we demonstrate that en activity programs wing cells to express hh whereas the absence of en activity programs them to respond to hh by expressing dpp. As a consequence, posterior cells secrete hh and induce a stripe of neighboring anterior cells across the compartment boundary to secrete dpp. Second, we demonstrate that dpp can exert a long-range organizing influence on surrounding wing tissue, specifying anterior or posterior pattern depending on the compartmental provenance, and hence the state of en activity, of the responding cells. Thus, dpp secreted by anterior cells along the compartment boundary has the capacity to organize the development of both compartments. Finally, we report evidence suggesting that dpp may exert its organizing influence by acting as a gradient morphogen in contrast to hh which appears to act principally as a short range inducer of dpp.
TL;DR: The results support the idea that Delta- and Notch-like proteins are involved in cell-to-cell communication in mammalian embryos and suggest a role for these proteins in cellular interactions underlying somitogenesis and development of the nervous system.
Abstract: The Drosophila Delta (Dl) gene is essential for cell-cell communication regulating the determination of various cell fates during development. Dl encodes a transmembrane protein, which contains tandem arrays of epidermal-growth-factor-like repeats in the extracellular domain and directly interacts with Notch, another transmembrane protein with similar structural features, in a ligand-receptor-like manner. Similarly, cell-cell interactions involving Delta-like and Notch-like proteins are required for cell fate determinations in C. elegans. Notch homologues were also isolated from several vertebrate species, suggesting that cell-to-cell signaling mediated by Delta- and Notch-like proteins could also underlie cell fate determination during vertebrate development. However, in vertebrates, no Delta homologues have yet been described. We have isolated a novel mouse gene, Dll1 (delta-like gene 1), which maps to the mouse t-complex and whose deduced amino acid sequence strongly suggests that Dll1 represents a mammalian gene closely related to Drosophila Delta. Dll1 is transiently expressed during gastrulation and early organogenesis, and in a tissue-restricted manner in adult animals. Between day 7 and 12.5 of development, expression was detected in the paraxial mesoderm, closely correlated with somitogenesis, and in subsets of cells in the nervous system. In adult animals, transcripts were detected in lung and heart. Dll1 expression in the paraxial mesoderm and nervous system is strikingly similar to the expression of mouse Notch1 during gastrulation and early organogenesis. The overlapping expression patterns of the Dll1 and Notch1 genes suggest that cells in these tissues can communicate by interaction of the Dll1 and Notch1 proteins. Our results support the idea that Delta- and Notch-like proteins are involved in cell-to-cell communication in mammalian embryos and suggest a role for these proteins in cellular interactions underlying somitogenesis and development of the nervous system.
TL;DR: The RBP-J kappa gene was revealed to be essential for postimplantation development of mice and was shown to be identical to Suppressor of Hairless [Su(H)] which plays important roles in the development of the peripheral nervous system.
Abstract: The RBP-J kappa protein is a transcription factor that recognizes the sequence C(T)GTGGGGA. The RBP-J kappa gene is highly conserved in a wide variety of species and the Drosophila homologue has been shown to be identical to Suppressor of Hairless [Su(H)] which plays important roles in the development of the peripheral nervous system. To explore the function of the RBP-J kappa gene in mouse embryogenesis, a mutation was introduced into the functional RBP-J kappa gene in embryonic stem (ES) cells by homologous recombination. Null mutant ES cells survived but null mutant mice showed embryonic lethality before 10.5 days of gestation. The mutant mice showed severe growth retardation as early as 8.5 days of gestation. Developmental abnormalities, including incomplete turning of the body axis, microencephaly, abnormal placental development, anterior neuropore opening and defective somitogenesis, were observed in the mutant mice at 9.5 days of gestation. RBP-J kappa mutant embryos expressed a posterior mesodermal marker FGFR1. Their irregularly shaped somites expressed a somite marker gene Mox 1 but failed to express myogenin. The RBP-J kappa gene was revealed to be essential for postimplantation development of mice.
TL;DR: Comparisons between the development of wild- type and mutant petals or leaves reveal that phan acts early in development of these lateral organs, suggesting that phandependent dorsal cell identity is required for lateral growth of the wild-type leaf and petal lobe.
Abstract: To understand better the mechanisms that lead to dorsoventrality in the lateral organs of plants, mutants at the phantastica (phan) locus of Antirrhinum majus have been identified and characterised. The leaves, bracts and petal lobes of phan mutants show varying degrees of reduction in dorsal tissues, indicating that phan is required for establishing dorsal cell identity. Each phan mutant produces a variety of different leaf morphologies, but has a characteristic and relatively constant floral phenotype. In several different forms of phan mutant leaves and petal lobes, novel boundaries between dorsal and ventral cell types form ectopic axes of growth, suggesting that phandependent dorsal cell identity is required for lateral growth of the wild-type leaf and petal lobe. Comparisons between the development of wild-type and mutant petals or leaves reveal that phan acts early in development of these lateral organs. The possible role of the phan gene in evolution of different leaf forms is discussed. SUMMARY
TL;DR: It is suggested that the prospective neural crest is induced in normal embryos in the ectoderm that overlies the junction of the domains that express noggin and Xwnt-8 and not NCAM although the mesoderm marker Xbra is also expressed.
Abstract: The earliest sign of the prospective neural crest of Xenopus is the expression of the ectodermal component of Xsna (the Xenopus homologue of snail) in a low arc on the dorsal aspect of stage 11 embryos, which subsequently assumes the horseshoe shape characteristic of the neural folds as the convergence-extension movements shape the neural plate. A related zinc-finger gene called Slug (Xslu) is expressed specifically in this tissue (i.e. the prospective crest) when the convergence extension movements are completed. Subsequently, Xslu is found in pre- and post-migratory cranial and trunk neural crest and also in lateral plate mesoderm after stage 17. Both Xslu and Xsna are induced by mesoderm from the dorsal or lateral marginal zone but not from the ventral marginal zone. From stage 10.5, explants of the prospective neural crest, which is underlain with tissue, are able to express Xslu. However expression of Xsna is not apparently specified until stage 12 and further contact with the inducer is required to raise the level of expression to that seen later in development. Xslu is specified at a later time. Embryos injected with noggin mRNA at the 1-cell stage or with plasmids driving noggin expression after the start of zygotic transcription express Xslu in a ring surrounding the embryo on the ventroposterior side. We suggest this indicates (a) that noggin interacts with another signal that is present throughout the ventral side of the embryo and (b) that Xslu is unable to express in the neural plate either because of the absence of a co-inducer or by a positive prohibition of expression. The ventral co-inducer, in the presence of overexpressed noggin, seems to generate an anterior/posterior pattern in the ventral part of the embryo comparable to that seen in neural crest of normal embryos. We suggest that the prospective neural crest is induced in normal embryos in the ectoderm that overlies the junction of the domains that express noggin and Xwnt-8. In support of this, we show animal cap explants from blastulae and gastrulae, treated with bFGF and noggin express Xslu but not NCAM although the mesoderm marker Xbra is also expressed. Explants treated with noggin alone express NCAM only. An indication that induction of the neural plate border is regulated independently of the neural plate is obtained from experiments using ultraviolet irradiation in the precleavage period. At certain doses, the cranial crest domains are not separated into lateral masses and there is a reduction in the size of the neural plate.
TL;DR: Results suggest that anterior endoderm contains signaling molecules that can induce cardiac myocyte specification of early primitive streak cells, and one of the cardiac muscle markers induced by anteriorendoderm, cNkx-2.5, is here described for the first time.
Abstract: An experimental system was devised to study the mechanisms by which cells become committed to the cardiac myocyte lineage during avian development. Chick tissues from outside the fate map of the heart (in the posterior primitive streak {PPS} of a Hamburger & Hamilton stage 4 embryo) were combined with potential inducing tissues from quail embryos and cultured in vitro. Species-specific RT-PCR was employed to detect the appearance of the cardiac muscle markers chick Nkx-2.5 (cNkx-2.5), cardiac troponin C and ventricular myosin heavy chain in the chick responder tissues. Using this procedure, we found that stage 4-5 anterior lateral (AL) endoderm and anterior central (AC) mesendoderm, but not AL mesoderm or posterior lateral mesendoderm, induced cells of the PPS to differentiate as cardiac myocytes. Induction of cardiogenesis was accompanied by a marked decrease in the expression of ρ-globin, implying that PPS cells were being induced by anterior endoderm to become cardiac myocytes instead of blood-forming tissue. These results suggest that anterior endoderm contains signaling molecules that can induce cardiac myocyte specification of early primitive streak cells. One of the cardiac muscle markers induced by anterior endoderm, cNkx-2.5, is here described for the first time. cNkx-2.5 is a chick homeobox-containing gene that shares extensive sequence similarity with the Drosophila gene tinman, which is required for Drosophila heart formation. The mesodermal component of cNkx-2.5 expression from stage 5 onward, as determined by in situ hybridization, is strikingly in accord with the fate map of the avian heart. By the time the myocardium and endocardium form distinct layers, cNkx-2.5 is found only in the myocardium. cNkx-2.5 thus appears to be the earliest described marker of avian mesoderm fated to give rise to cardiac muscle. SUMMARY
TL;DR: Analysis of agametic flies revealed that somatic cells continue to divide in the absence of a germline, indicating that functional somatic stem cells have a finite life span.
Abstract: Throughout their lives, adult Drosophila females continuously produce oocytes, each surrounded by an epithelial monolayer of follicle cells. To characterize the somatic stem cells that give rise to ovarian follicle cells, we marked dividing cells using FLP-catalyzed mitotic recombination and analyzed the resulting clones. Each ovariole in young females contains, on average, two somatic stem cells located near the border of germarium regions 2a and 2b. The somatic stem cells do not coordinate their divisions either with each other or with the germline stem cells. As females age, initially mosaic ovarioles become monoclonal, indicating that functional somatic stem cells have a finite life span. Analysis of agametic flies revealed that somatic cells continue to divide in the absence of a germline. Under these conditions, the somatic stem cells develop near the tip of the ovariole (the normal site of the germline stem cells), and a subpopulation of somatic cells that normally separates the germline and somatic stem cells is missing.
TL;DR: Six mutations causing alterations in the radial organisation of the primary root of Arabidopsis thaliana are analysed andEmbryonic phenotypes resulting from wooden leg, gollum, pinocchio, scarecrow, shortroot and fass mutations are described.
Abstract: The primary root of Arabidopsis thaliana has a remarkably uniform cellular organisation. The fixed radial pattern of cell types in the mature root arises from proliferative divisions within the root meristem. The root meristem, in turn, is laid down during embryogenesis. We have analysed six mutations causing alterations in the radial organisation of the root. Embryonic phenotypes resulting from wooden leg, gollum, pinocchio, scarecrow, shortroot and fass mutations are described. While mutations in the fass gene affect morphogenesis of all cells, the five other mutations cause alterations in specific layers. Wooden leg and gollum mutations interfere with the proper organisation of the vascular tissue. Shortroot, scarecrow and pinocchio affect the endodermis and cortex. The layer- specific phenotypes caused by all five mutations are also apparent in the hypocotyl. All these phenotypes originate from defects in the radial organisation of the embryonic axis. Secondary roots, which are formed post-embryonically, also display layer-specific phenotypes.