Endothelial and smooth muscle cells interact with each other to form new blood vessels. In this review, the cellular and molecular mechanisms underlying the formation of endothelium-lined channels (angiogenesis) and their maturation via recruitment of smooth muscle cells (arteriogenesis) during physiological and pathological conditions are summarized, alongside with possible therapeutic applications.

Mechanisms of angiogenesis and arteriogenesis.

Epithelial-mesenchymal transition is an indispensable mechanism during morphogenesis, as without mesenchymal cells, tissues and organs will never be formed. However, epithelial-cell plasticity, coupled to the transient or permanent formation of mesenchyme, goes far beyond the problem of cell-lineage segregation. Understanding how mesenchymal cells arise from an epithelial default status will also have a strong impact in unravelling the mechanisms that control fibrosis and cancer progression.

Complex networks orchestrate epithelial–mesenchymal transitions

Targeted gene disruption in the mouse shows that the Sonic hedgehog (Shh) gene plays a critical role in patterning of vertebrate embryonic tissues, including the brain and spinal cord, the axial skeleton and the limbs. Early defects are observed in the establishment or maintenance of midline structures, such as the notochord and the floorplate, and later defects include absence of distal limb structures, cyclopia, absence of ventral cell types within the neural tube, and absence of the spinal column and most of the ribs. Defects in all tissues extend beyond the normal sites of Shh transcription, confirming the proposed role of Shh proteins as an extracellular signal required for the tissue-organizing properties of several vertebrate patterning centres.

Cyclopia and defective axial patterning in mice lacking Sonic hedgehog gene function.

Two small RNAs regulate the timing of Caenorhabditis elegans development. Transition from the first to the second larval stage fates requires the 22-nucleotide lin-4 RNA and transition from late larval to adult cell fates requires the 21-nucleotide let-7 RNA. The lin-4 and let-7 RNA genes are not homologous to each other, but are each complementary to sequences in the 3' untranslated regions of a set of protein-coding target genes that are normally negatively regulated by the RNAs. Here we have detected let-7 RNAs of ~21 nucleotides in samples from a wide range of animal species, including vertebrate, ascidian, hemichordate, mollusc, annelid and arthropod, but not in RNAs from several cnidarian and poriferan species, Saccharomyces cerevisiae, Escherichia coli or Arabidopsis. We did not detect lin-4 RNA in these species. We found that let-7 temporal regulation is also conserved: let-7 RNA expression is first detected at late larval stages in C. elegans and Drosophila , at 48 hours after fertilization in zebrafish, and in adult stages of annelids and molluscs. The let-7 regulatory RNA may control late temporal transitions during development across animal phylogeny.

Conservation of the sequence and temporal expression of let-7 heterochronic regulatory RNA

Charge, Sophie B. P., and Michael A. Rudnicki. Cellular and Molecular Regulation of Muscle Regeneration. Physiol Rev 84: 209–238, 2004; 10.1152/physrev.00019.2003.—Under normal circumstances, mamma...

Cellular and Molecular Regulation of Muscle Regeneration

The chicken cardiac troponin T (cTnT) gene is representative of numerous cardiac and skeletal muscle-specific genes that contain muscle-CAT (MCAT) elements within their promoters. We examined the regulation of the chicken cTnT gene in vivo in zebrafish embryos, and in vitro in cardiomyocyte, myoblast, and fibroblast cultures. Defined regions of the cTnT promoter were linked to the green fluorescent protein (GFP) gene for in vivo analysis, and the luciferase gene for in vitro analysis. Injection of the cTnT promoter constructs into fertilized zebrafish eggs resulted in GFP expression in both heart and skeletal muscle cells reproducing the pattern of expression of the endogenous cTnT gene in the chicken embryo. Promoter deletion analysis revealed that the cis-regulatory regions responsible for cardiac and skeletal muscle-specific expression functioned in an equivalent manner in both in vitro and in vivo environments. In addition, we show that mutation of the poly-ADP ribose polymerase-I (PARP-I) binding site adjacent to the distal MCAT element in the chicken cTnT promoter produced a non-cell-specific promoter in vitro and in the zebrafish. Thus, the PARP-I transcriptional regulatory mechanism that governs muscle specificity of the chicken cTnT promoter is conserved across several chordate classes spanning at least 350 million years of evolution.

In vivo regulation of the chicken cardiac troponin T gene promoter in zebrafish embryos.

Publisher Summary This chapter outlines two basic procedures for the transplantation of quail embryo somites into chick embryos. Although the two methods were developed independently, both employ a remarkably similar surgical strategy, even down to the sequence of incisions. The similarity in incision sequence reflects mechanical constraints inherent to the tissues within the avian embryo. Nevertheless, combining materials or techniques from both procedures can exploit advantages and minimize disadvantages. In addition, these basic procedures can also be used to perform modified somite transplantations or transplantations of somite fragments. Tranplantation of somite fragments can be used to elucidate the fate of different portions of the developing somite. Half-somite transplantation has proven particularly useful in this regard because the somite can easily be divided in half along each of its three axes. The connections between half-somite fragments, however, are somewhat more fragile than those between whole somites, so more care must be taken in their isolation and transfer. The chapter also outlines half-somite transplantation strategies that have proven useful in revealing novel aspects of early development.

Avian somite transplantation: a review of basic methods.

Transgene expression in the QM myogenic cell line

Publisher Summary This chapter discusses the manipulation of the avian segmental plate in vivo  The avian embryo provides a useful experimental system for the investigation of vertebrate development To track the fate of experimentally manipulated cells in the embryo, cell-labeling techniques are required When combined with the tools of molecular biology, lineage tracing is a powerful tool for analyzing the mechanisms of cell specification and morphogenesis The quail–chick grafting method developed by Le Douarin has been successfully used as a cell-labeling technique in the avian embryo Organ anlagen in the chick embryo are marked by surgical replacement with the corresponding anlage from a quail embryo The cells generated by the grafted quail anlage can be identified in Feulgen-stained tissue sections by the presence of bright crimson nucleoli, which are absent from the pale-staining nuclei of host chick cells The method presented in this chapter describes the transplantation of fragments of the segmental plate, the precursor to the somites, which are the embryonic anlagen of the skeletal muscle and the axial skeleton

Manipulation of the avian segmental plate in vivo

To elucidate the distribution and function of mRNA in mouse kidney cytoplasm, we compared mRNA isolated from polysomal (greater than 80S) and native postpolysomal (20--80S) ribonucleoproteins with respect to synthesis and lifetime, sequence content, and translational activity. The 20--25% of cytoplasmic mRNA recovered from postpolysomal ribonucleoprotein is similar to polysomal mRNA in size (20--22S), in apparent half-life (11--13 h), in major products of cell-free translation, and in nucleotide complexity (approximately 4 x 10(7) nucleotides). The labeling kinetics of polysomal and postpolysomal mRNA suggest these mRNA populations are in equilibrium. [3H]cDNAs transcribed from polysomal and from postpolysomal poly(A)-containing mRNAs react with template mRNA and with the heterologous mRNA at the same rate (Cot1/2 approximately 6.3 mol.s/L) and to the same extent (95%). Therefore, these mRNAs are equally diverse and homologous and occur at similar relative frequencies. Postpolysomal mRNA directs cell-free protein synthesis at only approximately 30% of the rate of polysomal mRNA and to only 30% of the extent of mRNA from polysomes. Postpolysomal mRNA is approximately 3-fold less sensitive than polysomal mRNA to inhibition of translation by m7GMP, suggesting postpolysomal mRNA contains a greater fraction of molecules deficient in 5'-terminal caps. Postpolysomal mRNA may derive from renal mRNAs that initiate translation inefficiently and thus accumulate as postpolysomal ribonucleoproteins.

Charles P. Ordahl

Papers

In vivo regulation of the chicken cardiac troponin T gene promoter in zebrafish embryos.

Avian somite transplantation: a review of basic methods.

Transgene expression in the QM myogenic cell line

Manipulation of the avian segmental plate in vivo

Mouse kidney nonpolysomal mRNA: metabolism, coding function, and translational activity