Retinoic acid activates two pathways required for meiosis in mice.
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ABSTRACT:
SUBMITTER: Koubova J
PROVIDER: S-EPMC4125102 | biostudies-literature | 2014 Aug
REPOSITORIES: biostudies-literature
Publications
Retinoic acid activates two pathways required for meiosis in mice.
Koubova Jana J Hu Yueh-Chiang YC Bhattacharyya Tanmoy T Soh Y Q Shirleen YQ Gill Mark E ME Goodheart Mary L ML Hogarth Cathryn A CA Griswold Michael D MD Page David C DC
PLoS genetics 20140807 8
In all sexually reproducing organisms, cells of the germ line must transition from mitosis to meiosis. In mice, retinoic acid (RA), the extrinsic signal for meiotic initiation, activates transcription of Stra8, which is required for meiotic DNA replication and the subsequent processes of meiotic prophase. Here we report that RA also activates transcription of Rec8, which encodes a component of the cohesin complex that accumulates during meiotic S phase, and which is essential for chromosome syna ...[more]
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Project description:To help understand the elusive mechanisms of zebrafish sex determination, we studied the genetic machinery regulating production and breakdown of retinoic acid (RA) during the onset of meiosis in gonadogenesis. Results uncovered unexpected mechanistic differences between zebrafish and mammals. Conserved synteny and expression analyses revealed that cyp26a1 in zebrafish and its paralog Cyp26b1 in tetrapods independently became the primary genes encoding enzymes available for gonadal RA-degradation, showing lineage-specific subfunctionalization of vertebrate genome duplication (VGD) paralogs. Experiments showed that zebrafish express aldh1a2, which encodes an RA-synthesizing enzyme, in the gonad rather than in the mesonephros as in mouse. Germ cells in bipotential gonads of all zebrafish analyzed were labeled by the early meiotic marker sycp3, suggesting that in zebrafish, the onset of meiosis is not sexually dimorphic as it is in mouse and is independent of Stra8, which is required in mouse but was lost in teleosts. Analysis of dead-end knockdown zebrafish depleted of germ cells revealed the germ cell-independent onset and maintenance of gonadal aldh1a2 and cyp26a1 expression. After meiosis initiated, somatic cell expression of cyp26a1 became sexually dimorphic: up-regulated in testes but not ovaries. Meiotic germ cells expressing the synaptonemal complex gene sycp3 occupied islands of somatic cells that lacked cyp26a1 expression, as predicted by the hypothesis that Cyp26a1 acts as a meiosis-inhibiting factor. Consistent with this hypothesis, females up-regulated cyp26a1 in oocytes that entered prophase-I meiotic arrest, and down-regulated cyp26a1 in oocytes resuming meiosis. Co-expression of cyp26a1 and the pluripotent germ cell stem cell marker pou5f1(oct4) in meiotically arrested oocytes was consistent with roles in mouse to promote germ cell survival and to prevent apoptosis, mechanisms that are central for tipping the sexual fate of gonads towards the female pathway in zebrafish.
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Project description:Meiosis is a specialized form of cell division essential for sexual reproduction. The unique cellular events of meiosis have been extensively studied in model eukaryotes, including mammals. In mammals, the molecular and cellular changes that germ cells must undergo to transition from mitotic spermatogonia to meiotic spermatocytes remain largely undefined. Retinoic acid (RA) has been proposed as the meiosis inducing substance (MIS) required for female and male meiotic initiation. However, evidence for this presumption is based on studies of fetal gonads – meiosis is initiated in fetal ovaries but suppressed in fetal testes. Critically, the requirement for RA in meiosis has never been formally tested because germ cell differentiation and meiotic initiation in the fetal ovary are temporally inseparable. Using the postnatal mouse testis, where differentiation and meiotic initiation are temporally distinct (8.6 days apart), we test the hypothesis that RA is dispensable for initiation and progression through meiosis. Complementary in vivo experimental models were designed to address the hypothesis. In the first, “RA-sufficient” (RA-suf) model, spermatogenesis was synchronized by administration of potent and selective RA synthesis inhibitor; as a result, testes contained only undifferentiated spermatogonia. Then, the inhibitor was discontinued, and mice were given a single dose of exogenous RA to initiate spermatogonial differentiation. Germ cells completed differentiation, entered and completed meiosis, and formed haploid gametes at predicted timepoints. In the second, “RA-deficient” (RA-def) model, mice were treated as above, except the inhibitor was administered continuously. The lack of testicular RA in this model was confirmed in multiple ways, including assessment of RA-responsive gene expression, in vitro serum-free cultures, and dose-response experiments. To our surprise, germ cells in RA-def testes completed differentiation, underwent meiotic DNA replication, completed the landmark cytological processes of meiosis, and formed postmeiotic haploid spermatids, all on the predicted timeline of the RA-suf model. To define the effect of RA-deficiency on gene expression during meiotic initiation, large, highly enriched populations of premeiotic spermatogonia from RA-suf mice, and meiotic preleptotene spermatocytes from both models were FACS-isolated and subjected to bulk RNA-seq. Interestingly, analyses revealed few significant differences in expression of characteristic meiotic genes at the mRNA level. However, genes that were significantly different between RA-suf and RA-def preleptotene spermatocytes were associated with spermiogenesis functions. Taken together, our data reveal that, after initiating spermatogonial differentiation, RA is dispensable for initiation, progression through, and completion of meiosis in the male germline.
2023-07-03 | GSE194376 | GEO
Project description:Substantial evidence exists that during fetal ovarian development in mammals, retinoic acid (RA) induces germ cells to express the pre-meiotic marker Stra8 and enter meiosis, and that these effects are prevented in the fetal testis by the RA-degrading P450 enzyme CYP26B1. Nonetheless, the role of RA has been disputed principally because germ cells in embryos lacking two major RA-synthesizing enzymes, ALDH1A2 and ALDH1A3, remain able to enter meiosis. Here we show that a third RA-synthesizing enzyme, ALDH1A1, is expressed in fetal ovaries, providing a likely source of RA in the absence of ALDH1A2 and ALDH1A3. In ovaries lacking ALDH1A1, the onset of germ cell meiosis is delayed. Our data resolve the conundrum posed by conflicting published data sets and reconfirm the model that meiosis is triggered by endogenous RA in the developing ovary.
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