Defective mesonephric cell migration is associated with abnormal testis cord development in C57BL/6J XY(Mus domesticus) mice.
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During the critical period of mouse sex determination, mesenchymal cells migrate from the mesonephros into the adjacent developing testis. This process is thought to initiate cord development and is dependent on Sry. The presence of Sry, however, does not always guarantee normal testis development. For example, transfer of certain Mus domesticus-derived Y chromosomes, i.e., M. domesticus Sry alleles, onto the C57BL/6J (B6) inbred mouse strain results in abnormal testis development. We tested the hypothesis that mesonephric cell migration was impaired in three cases representing a range of aberrant testis development: B6 XY(AKR), B6 XY(POS), and (BXD-21 x B6-Y(POS))F1 XY(POS). In each case, mesonephric cell migration was abnormal. Furthermore, the timing, extent, and position of migrating cells in vitro and cord development in vivo were coincident, supporting the hypothesis that mesonephric cells are critical for cord development. Additional experiments indicated that aberrant testis development results from the inability of Sry(M. domesticus) to initiate normal cell migration, but that downstream signal transduction mechanisms are intact. These experiments provide new insight into the mechanism of C57BL/6J-Y(M. domesticus) sex reversal. We present a model incorporating these findings as they relate to mammalian sex determination. (+info)
Sex gene pool evolution and speciation: a new paradigm.
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In this paper, we review the literature on the growing body of data demonstrating the rapid evolution of sex and reproduction related (SRR) genes and show how a paradigm shift to the study of SRR genes can provide new approaches to solving some of the old problems in evolutionary biology. The argument is based on (1) the growing scope and importance of sexual selection in evolution, (2) the growing number of case studies showing rapid evolution of sexual traits in a wide variety of taxa, (3) the faster rate of DNA sequence divergence in genes affecting sexual function and fertility, (4) the evidence for the involvement of novel traits/genes in sexual functions, and (5) a proposed sex/non-sex dichotomy of the gene pool affecting viability versus fertility. It is argued that the adoption of the sex/non-sex dichotomy of genes/traits can provide new perspectives on such problems as species concepts, modes (allopatric/sympatric) of speciation, Haldane's rule, reinforcement, and the founder effect. It is proposed that the evolutionary study of genes affecting viability versus fertility is the key to understanding the genetic basis of speciation. (+info)
Aberrant spermatogenesis and the peculiar mechanism of sex determination in Symphypleonan Collembola (Insecta).
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Light and electron microscopy evidence have been obtained to describe the peculiar spermatogenesis in the collembolan species Sminthurus viridis and Allacma fusca (Sminthuridae). In these two species, the two sexes differ for the lack of two chromosomes (the sex chromosomes) in males (males, 2n = 10; females, 2n = 12). While oogenesis seems to proceed normally, spermatogenesis is peculiar because the two daughter cells of the first meiotic division have different chromosome numbers (six and four). The cell receiving four chromosomes degenerates, while the cell receiving six chromosomes completes meiosis and produces identical spermatozoa (n = 6). At fertilization, pronuclei with six chromosomes fuse together to form zygotes with 2n = 12. Male embryos must lose two sex chromosomes during the first zygotic mitosis, as all male cells have 2n = 10 chromosomes. The sex chromosome system of these species can be identified as X1X1X2X2:X1X20. Electron microscopy observations show that the same peculiar spermatogenesis occurs also in two others species of the same family, Caprainea marginata and Lipothrix lubbocki. The peculiar sex determination system described is similar but not identical to what is observed in other insect orders, and it may represent an evolutionary step toward parthenogenesis. It is suggested that this peculiar spermatogenesis is common to all Symphypleona. (+info)
Sex determination: co-opted signals determine gender.
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The Drosophila JAK-STAT pathway and its ligand Unpaired are required for a wide range of developmental processes. Recent results have identified Unpaired as an activator of sex-lethal and revealed a new role for the JAK-STAT pathway in sex determination. (+info)
Mab-3 is a direct tra-1 target gene regulating diverse aspects of C. elegans male sexual development and behavior.
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Sex determination is controlled by global regulatory genes, such as tra-1 in Caenorhabditis elegans, Sex lethal in Drosophila, or Sry in mammals. How these genes coordinate sexual differentiation throughout the body is a key unanswered question. tra-1 encodes a zinc finger transcription factor, TRA-1A, that regulates, directly or indirectly, all genes required for sexual development. mab-3 (male abnormal 3), acts downstream of tra-1 and is known to be required for sexual differentiation of at least two tissues. mab-3 directly regulates yolk protein transcription in the intestine and specifies male sense organ differentiation in the nervous system. It encodes a transcription factor related to the products of the Drosophila sexual regulator doublesex (dsx), which also regulates yolk protein transcription and male sense-organ differentiation. The similarities between mab-3 and dsx led us to suggest that some aspects of sex determination may be evolutionarily conserved. Here we find that mab-3 is also required for expression of male-specific genes in sensory neurons of the head and tail and for male interaction with hermaphrodites. These roles in male development and behavior suggest further functional similarity to dsx. In male sensory ray differentiation we find that MAB-3 acts synergistically with LIN-32, a neurogenic bHLH transcription factor. Expression of LIN-32 is spatially restricted by the combined action of the Hox gene mab-5 and the hairy homolog lin-22, while MAB-3 is expressed throughout the lateral hypodermis. Finally, we find that mab-3 transcription is directly regulated in the intestine by TRA-1A, providing a molecular link between the global regulatory pathway and terminal sexual differentiation. (+info)
The LAMMER protein kinase encoded by the Doa locus of Drosophila is required in both somatic and germline cells and is expressed as both nuclear and cytoplasmic isoforms throughout development.
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Activity of the Darkener of apricot (Doa) locus of Drosophila melanogaster is required for development of the embryonic nervous system, segmentation, photoreceptor maintenance, normal transcription, and sexual differentiation. The gene encodes a protein kinase, with homologues throughout eukaryotes known as the LAMMER kinases. We show here that DOA is expressed as at least two different protein isoforms of 105 and 55 kD throughout development, which are primarily localized to the cytoplasm and nucleus, respectively. Doa transcripts and protein are expressed in all cell types both during embryogenesis and in imaginal discs. Although it was recently shown that DOA kinase is essential for normal sexual differentiation, levels of both kinase isoforms are equal between the sexes during early pupal development. The presence of the kinase on the cell membrane and in the nuclei of polytene salivary gland cells, as well as exclusion from the nuclei of specific cells, may be indicative of regulated kinase localization. Mosaic analysis in both the soma and germline demonstrates that Doa function is essential for cell viability. Finally, in contrast to results reported in other systems and despite some phenotypic similarities, genetic data demonstrate that the LAMMER kinases do not participate in the ras-MAP kinase signal transduction pathway. (+info)
Wpkci, encoding an altered form of PKCI, is conserved widely on the avian W chromosome and expressed in early female embryos: implication of its role in female sex determination.
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Two W chromosome-linked cDNA clones, p5fm2 and p5fm3, were obtained from a subtracted (female minus male) cDNA library prepared from a mixture of undifferentiated gonads and mesonephroi of male or female 5-d (stages 26-28) chicken embryos. These two clones were demonstrated to be derived from the mRNA encoding an altered form of PKC inhibitor/interacting protein (PKCI), and its gene was named Wpkci. The Wpkci gene reiterated approximately 40 times tandemly and located at the nonheterochromatic end of the chicken W chromosome. The W linkage and the moderate reiteration of Wpkci were conserved widely in Carinatae birds. The chicken PKCI gene, chPKCI, was shown to be a single-copy gene located near the centromere on the long arm of the Z chromosome. Deduced amino acid sequences of Wpkci and chPKCI showed approximately 65% identity. In the deduced sequence of Wpkci, the HIT motif, which is essential for PKCI function, was absent, but the alpha-helix region, which was conserved among the PKCI family, and a unique Leu- and Arg-rich region, were present. Transcripts from both Wpkci and chPKCI genes were present at significantly higher levels in 3- to 6-d (stages 20-29) embryos. These transcripts were detected in several embryonic tissues, including undifferentiated left and right gonads. When the green fluorescent protein-fused form of Wpkci was expressed in male chicken embryonic fibroblast, it was located almost exclusively in the nucleus. A model is presented suggesting that Wpkci may be involved in triggering the differentiation of ovary by interfering with PKCI function or by exhibiting its unique function in the nuclei of early female embryos. (+info)
Large-scale screen for genes involved in gonad development.
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The vertebrate gonad develops from the intermediate mesoderm as an initially bipotential organ anlage, the genital ridge. In mammals, Sry acts as a genetic switch towards testis development. Sox9 has been shown to act downstream of Sry in testis development, while Dax1 appears to counteract Sry. Few more genes have been implicated in early gonad development. However, the genetic networks controlling early differentiation events in testis and ovary are still far from being understood. In order to provide a broader basis for the molecular analysis of gonad development, high-throughput gene expression analysis was utilized to identify genes specifically expressed in the gonad. In total, among 138 genes isolated which showed tissue specific expression in the embryo, 79 were detected in the developing gonad or sex ducts. Twenty-seven have not been functionally described before, while 40 represent known genes and 12 are putative mouse orthologues. Forty-five of the latter two groups (86%) have not been described previously in the fetal gonad. In addition, 21 of the gonad specific genes showed sex-dimorphic expression suggesting a role in sex determination and/or gonad differentiation. Eighteen of the latter (86%) have not been described previously in the fetal gonad. In total we provide new data on 72 genes which may play a role in gonad or sex duct development and/or sex determination. Thus we have generated a large gene resource for the investigation of these processes, and demonstrate the suitability of high-throughput gene expression screening for the genetic analysis of organogenesis. (+info)