Showing papers on "Dosage compensation published in 1983"

Sex determination and dosage compensation in Drosophila melanogaster: production of male clones in XX females.

Abstract: Sex determination and dosage compensation in Drosophila are implemented by the ratio of X-chromosomes to sets of autosomes (X:A ratio). Our aim was to change this X:A ratio during development, and to assess the response of the affected cells in sexually dimorphic structures. For this purpose, clones of XO constitution were produced in female embryos and larvae of two genotypes in which almost the entire euchromatic arm of one X-chromosome was translocated to the third chromosome. Genotype I was heterozygous for the X-linked recessive mutations Sxl, genotype II was homozygous for Sxl. The Sxl gene (sex-lethal) is involved in mediating sex determination and dosage compensation. In genotype I (Sxl), male clones could be generated up to 48 h in genitalia and analia, up to 72 h in the sex comb region and up to 96 h in 5th and 6th tergites. In genotype II (Sxl), male clones only appeared in the tergites, and only up to 24 h. The difference in these results is ascribed to the presence of Sxl in genotype I: when homozygous, this mutation causes XX clones to differentiate male structures; most of the male clones produced in genotype I must therefore be XX. In contrast, male clones produced in genotype II must be XO. Since these were only found when generated in embryos we conclude that the X:A ratio expresses itself autonomously in clones by setting the state of activity of the Sxl gene around blastoderm stage. Once this is achieved, the X:A signal is no longer needed, and the state of activity of the Sxl gene determines sex and dosage compensation.

X chromosome dosage and gene expression in Caenorhabditis elegans: Two unusual dumpy genes

Abstract: The phenotypes caused by mutations in two autosomal genes of the nematode Caenorhabditis elegans, dpy-21 V and dpy-26 IV, are markedly affected by X chromosome dosage, independent of sexual phenotype. At high X chromosome to autosome ratio, in 2A; 3X animals, these dumpy mutations are lethal; at intermediate ratio, in 2A; 2X animals, they cause dumpiness or lethality; at low ratio, in 2A; 1X animals they cause neither dumpiness nor lethality. One gene, dpy-26, exhibits a strong maternal effect. Interaction between these genes and two major sex-determining genes her-1 V and tra-1 III have been examined. The dumpy mutations partly suppress the masculinization of tra-1 2A;2X animals and also increase the fertility of most her-1 2A;1X hermaphrodites. It is suggested that these dumpy genes are involved in X chromosome dosage compensation, and in some aspects of sexual differentiation. The dpy-26 gene is compared with a similar Drosophila gene, daughterless.

X-chromosome activity in female mouse embryos heterozygous for Pgk-1 and Searle's translocation, T(X; 16) 16H.

Abstract: To investigate whether the preferential expression of genes on the translocated X chromosome in female mice carrying the X-autosome translocation T(X; 16)16H (Searle's translocation) is due to non-random inactivation or to cell selection, we examined tissues of mouse embryos heterozygous for the X-linked gene coding for phosphoglycerate kinase (Pgk-1). From the cross T16H Pgk-lb/+ Pgk-lb ♀ × +Pgk-la / Y ♂, embryos expressing both isozymic forms of PGK-1 in the epiblast, and only the maternally inherited Pgk-lb allele in extra-embryonic tissues, were assumed to be chromosomally balanced, heterozygous female embryos carrying the Searle's translocation (like the mother). The normal X chromosome in this cross carries a high-expression Xcec locus. At 6 days post-coitum (p.c.) both isozymes were equally expressed in the epiblast as expected if both X chromosomes are active, but by 7 days p.c. the PGK-1B contribution was significantly less than 50%, suggesting that X inactivation has occurred with a bias towards inactivation of the translocated X chromosome carrying the lower-expression Xce allele. By 8 days p.c. the situation was the reverse, with a Pgk-lb contribution of significantly more than 50%, and by 12½ days p.c. no Pgk-la expression could be detected. We interpret the dramatic change in isozy me expression between 7 and 8 days p.c. as indicating rapid selection against cells that had inactivated the translocated 16X chromosome. Two 7-day p.c. embryos unexpectedly showed equal expression of both Pgk-1 alleles in both embryonic and extra-embryonic tissues; these were presumably chromosomally unbalanced embryos which had inherited from the mother both an active translocated 16X chromosome carrying Pgk-lb and an active normal X chromosome carrying Pgk-la.

Male-Specific Lethal Mutations of DROSOPHILA MELANOGASTER . II. Parameters of Gene Action during Male Development.

Abstract: The male-specific lethal mutations ( msl 9s) identify loci whose wild-type gene products are essential for male, but not female, viability. Earlier studies in which X -linked gene activities were monitored in msl/msl male larvae demonstrated that these genes are responsible for setting and/or maintaining the level of X chromosome transcription in males ( i.e. , they are necessary for proper dosage compensation). The present study examines several important questions concerning their mode of action during development—The results of an examination of the effects of an msl-1 deficiency on male-lethal phase and female viability suggest that this mutation is an amorph, or a severe hypomorph. The effects of rendering a fly mutant for more than one male-lethal mutation were also examined. Multiply mutant flies were no more severely affected than singly mutant ones. A gynandromorph analysis revealed that the male-limited lethality associated with msl-2 has no single lethal focus. Somatic clones of homozygous msl-2 cells were initiated at various times during development by X-ray-induced mitotic recombination. An examination of the viability, growth patterns and morphology of marked clones demonstrated that: (1) msl-2 + acts in a cell autonomous manner, (2) msl-2 + function is required not only in larval (polytene) cells as was shown in previous work but is also needed in the diploid cells that give rise to adult structures, (3) the msl-2 + gene is needed fairly late in development and perhaps continuously, (4) the msl-2 mutation does not affect sexual differentiation.

Differential NOR activities in somatic and germ cells of Monodelphis domestica (Marsupialia, Mammalia).

Abstract: Somatic and germ cells of the gray short-tailed opossum (Monodelphis domestica) were analyzed cytogenetically by C-banding, G-banding, and silver staining. The diploid chromosome number was found to be 18. C-banding revealed constitutive heterochromatin at the centromeres of all chromosomes, with additional heterochromatin on one arm of the Y. Silver staining for the localization of nucleolus organizer regions (NORs) showed NORs on the X and on a pair of autosomes, tentatively designated as chromosome 5. In females, the NORs on both X chromosomes were active in 98.3% of all somatic cells analyzed, indicating that this locus escapes sex-chromosome dosage compensation. Chromosome 5 showed an active NOR in only 16.2% of cells scored from the six females. In males, 100% of the somatic cells analyzed showed an active NOR on the X chromosome. Greater variability of autosomal NOR activity was observed between male individuals and between different tissues of the same male. Silver staining of pachytene spermatocytes revealed that (1) only an autosomal NOR was active, whereas the NOR of the X chromosome was inactive, and (2) the X and Y chromosomes showed asynaptic behavior, even though all autosomal synaptonemal complexes were fully formed during this stage.

X-chromosome inactivation and evolution in marsupials and other mammals.

Abstract: Sex chromosome dosage compensation in Australian marsupials exhibits several characteristics not ordinarily manifested in eutherian mammals. They are: 1) preferential inactivation of the paternally derived X-chromosome in somatic tissues; 2) a state of partial inactivity at some paternally derived X-linked gene loci in some cells; 3) absence of dosage compensation in some cell types; 4) absence of nuclear sex dimorphism at interphase; 5) discordance between late DNA replication and gene inactivation in some cell types; 6) failure of the X-chromosome to behave as a single unit. Despite these seemingly major differences between the dosage compensation systems of Australian marsupials and eutherians, there are also many underlying similarities. We propose that the two systems arose from a common ancestral mechanism in which the X-chromosome was regulated in a piecemeal fashion, rather than as a whole. To determine more precisely the sequence and timing of evolutionary events, we have initiated an investigation of dosage compensation in American marsupials, which diverged from Australian marsupials soon after the divergence of marsupials from eutherian mammals.

Developmental aspects of X chromosome inactivation in eutherian and metatherian mammals.

Abstract: The single active X principle has served for two decades as a focal point for research on the cyclic activation and inactivation of gene loci. Differences in X chromosome inactivation patterns of eutherian and marsupial mammals provide probes for investigating the mechanisms of the X inactivation process. In eutherian mammals, the X chromosome is inactivated early in meiotic prophase in males and remains inactive throughout the rest of spermatogenesis. During meiosis in females, the inactive X chromosome is activated so that both X chromosomes are active in oocytes. During the early cleavage divisions of female embryos, the paternally derived X is activated. It and the maternally derived X remain active until differentiation begins in early embryogenesis. At that time, the paternally derived X is inactivated in cells that give rise to extraembryonic membranes, whereas a random process determines which X chromosome is inactivated in cells that give rise to the embryo itself. Although less is known about developmental aspects of X inactivation in female marsupials, it is clear that the paternal X is preferentially inactive in postembryonic somatic cells. Furthermore, the paternal X is partially active at some loci in some cell types, indicating that it is not regulated as a single unit. The successful adaptation of a small (80–150 g), fecund marsupial to simple laboratory conditions now enables extensive experimentation on the large number of marsupials at various developmental stages. This capability, coupled with the application of newly developed cellular and molecular techniques to questions about X chromosome inactivation, shows great promise for advancing our understanding of the mechanisms that control the cyclic behavior of X chromosome activity.

Vital genes that flank sex-lethal, an x-linked sex-determining gene of drosophila melanogaster

Abstract: The X-chromosome:autosome balance in D. melanogaster appears to control both sex determination and dosage compensation through effects on a maternally influenced sex-linked gene called Sex-lethal (Sxl; 1-19.2). To facilitate molecular and genetic analysis of Sxl, we attempted to determine the locations of all ethyl methanesulfonate (EMS)-mutable genes vital to both sexes in the region between 6E1 and 7B1. This area includes approximately 1 cM of the genetic map on each side of Sxl and was reported by C. B. Bridges to contain 26 salivary gland polytene chromosome bands. The region appears rather sparsely populated with genes vital to both sexes, since the 122 recessive lethal mutations we recovered fell into only nine complementation groups. From one to 38 alleles of each gene were recovered. There was a preponderance of embryonic lethals in this area, although the lethal periods of loss-of-function mutations included larval, pupal and adult stages as well. Since the screen required that mutations be recessive and lethal to males, our failure to recover new Sxl alleles was the result expected for a gene with a female-specific function. An attempt was made to identify recessive male-specific lethals in this region, but none were found. Precise map positions were determined for eight of the nine vital genes. An interesting feature of the map is the location of Sxl in the middle of a 0.6- to 0.7-cM interval that appears to be devoid of genes vital to both sexes. The genetic location was determined of breakpoints near Sxl for all available chromosome rearrangements. Sxl is most likely located just to the left of band 7A1. We determined the relationship of our EMS-induced mutations in these nine genes to alleles induced by others. From this we conclude that the various genes appear to differ significantly from each other in their relative sensitivity to mutation by EMS vs. X rays.

Dosage compensation in drosophila: nadp-enzyme activities and cross-reacting material

Abstract: The relationships between gene dosage, enzyme activities and CRM levels have been determined for G6PD and 6PGD. Enzyme activities and CRM levels were directly proportional and increased in genotypes carrying duplications of the respective structural genes. When a duplication consisting of the distal 45% of the X chromosome was used to duplicate Pgd+, 6PGD activity and CRM increased and G6PD activity decreased. When the proximal 55% of the X chromosome was duplicated, G6PD activity and CRM increased whereas 6PGD activity and CRM levels decreased. These observations support the model of dosage compensation of X-linked genes that invokes an autosomal activator in limited concentrations for which X-linked loci compete. The distal 45% of the X chromosome, when duplicated, caused a significant increase in NADP-malic enzyme activity and CRM levels, as if a structural gene for NADP-ME is sex-linked.

Studies on the sex-specific lethals of Drosophila melanogaster. VI. An autosomal, recessive, non-maternal effect female-specific lethal mutant.

Abstract: A recessive, non-maternal effect, female-specific lethal mutant of Drosophila melanogaster was recovered from a natural population The mutant, fle(3)100, is located at 3-45± About one-half of homozygous females show normal development up to the pharate adult stage Salivary gland chromosomes of third instar homozygous female larvae have normal staining properties in the lactic-aceto-orcein staining, suggesting normal dosage compensation The results indicate that the fle(3)100 gene forms a new class of sex-specific lethals