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Retinoic Acid signalling and the control of meiotic entry in the human fetal gonad.

Childs AJ, Cowan G, Kinnell HL, Anderson RA, Saunders PT - PLoS ONE (2011)

Bottom Line: The development of mammalian fetal germ cells along oogenic or spermatogenic fate trajectories is dictated by signals from the surrounding gonadal environment.Aspects of this model are hard to reconcile with the spatiotemporal pattern of germ cell differentiation in the human fetal ovary, however.We have therefore examined the expression of components of the RA synthesis, metabolism and signalling pathways, and their downstream effectors and inhibitors in germ cells around the time of the initiation of meiosis in the human fetal gonad.

View Article: PubMed Central - PubMed

Affiliation: Medical Research Council Human Reproductive Sciences Unit, The Queen's Medical Research Institute, University of Edinburgh, Edinburgh, United Kingdom. a.childs@ed.ac.uk

ABSTRACT
The development of mammalian fetal germ cells along oogenic or spermatogenic fate trajectories is dictated by signals from the surrounding gonadal environment. Germ cells in the fetal testis enter mitotic arrest, whilst those in the fetal ovary undergo sex-specific entry into meiosis, the initiation of which is thought to be mediated by selective exposure of fetal ovarian germ cells to mesonephros-derived retinoic acid (RA). Aspects of this model are hard to reconcile with the spatiotemporal pattern of germ cell differentiation in the human fetal ovary, however. We have therefore examined the expression of components of the RA synthesis, metabolism and signalling pathways, and their downstream effectors and inhibitors in germ cells around the time of the initiation of meiosis in the human fetal gonad. Expression of the three RA-synthesising enzymes, ALDH1A1, 2 and 3 in the fetal ovary and testis was equal to or greater than that in the mesonephros at 8-9 weeks gestation, indicating an intrinsic capacity within the gonad to synthesise RA. Using immunohistochemistry to detect RA receptors RARα, β and RXRα, we find germ cells to be the predominant target of RA signalling in the fetal human ovary, but also reveal widespread receptor nuclear localization indicative of signalling in the testis, suggesting that human fetal testicular germ cells are not efficiently shielded from RA by the action of the RA-metabolising enzyme CYP26B1. Consistent with this, expression of CYP26B1 was greater in the human fetal ovary than testis, although the sexually-dimorphic expression patterns of the germ cell-intrinsic regulators of meiotic initiation, STRA8 and NANOS2, appear conserved. Finally, we demonstrate that RA induces a two-fold increase in STRA8 expression in cultures of human fetal testis, but is not sufficient to cause widespread meiosis-associated gene expression. Together, these data indicate that while local production of RA within the fetal ovary may be important in regulating the onset of meiosis in the human fetal ovary, mechanisms other than CYP26B1-mediated metabolism of RA may exist to inhibit the entry of germ cells into meiosis in the human fetal testis.

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Retinoic acid promotes the expression of STRA8 but not other meiosis-associated genes in the second trimester human fetal testis.Human fetal testis (14–15 weeks gestation) were disaggregated to a single cell suspension and cultured in serum free medium in the presence of vehicle (DMSO) or 1 µM all trans retinoic acid (1 µM RA in DMSO) for 24 hours. RA treatment induced a 2.2±0.3 fold increase in the expression of STRA8 (A) relative to vehicle treated controls (a vs b, p<0.05, n = 5), indicating that RA-regulated expression of this gene is conserved in human fetal gonads. No significant differences in the expression of meiosis markers SYCP3 (B, n.s. n = 6) or DMC1 (C, n = 6, n.s.) were detected between RA- and vehicle-treated cultures, indicating that whilst RA can stimulate STRA8 expression, it is not sufficient to cause widespread activation of the meiosis-associated gene expression programme. Values denote mean ± s.e.m..
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pone-0020249-g005: Retinoic acid promotes the expression of STRA8 but not other meiosis-associated genes in the second trimester human fetal testis.Human fetal testis (14–15 weeks gestation) were disaggregated to a single cell suspension and cultured in serum free medium in the presence of vehicle (DMSO) or 1 µM all trans retinoic acid (1 µM RA in DMSO) for 24 hours. RA treatment induced a 2.2±0.3 fold increase in the expression of STRA8 (A) relative to vehicle treated controls (a vs b, p<0.05, n = 5), indicating that RA-regulated expression of this gene is conserved in human fetal gonads. No significant differences in the expression of meiosis markers SYCP3 (B, n.s. n = 6) or DMC1 (C, n = 6, n.s.) were detected between RA- and vehicle-treated cultures, indicating that whilst RA can stimulate STRA8 expression, it is not sufficient to cause widespread activation of the meiosis-associated gene expression programme. Values denote mean ± s.e.m..

Mentions: To determine whether the induction of STRA8 expression by RA is conserved between mouse and human, we investigated the effects of RA treatment on cells from the second trimester human fetal testis. To ensure germ cell exposure to RA, fetal testes (14–15 weeks gestational age, n = 6) were disaggregated to a single cell suspension (thus uncoupling germ cells from their associated somatic cells which are in the mouse thought to be the site of CYP26B1 expression) and cultured in serum free medium in the presence of either vehicle (DMSO) or 1 µM all-trans RA for 24 hours. Expression of STRA8, and of the meiosis markers SYCP3 and DMC1 was then assessed by qRT-PCR in control and RA-treated cultures. Treatment with RA for 24 hours resulted in a 2.2±0.3 fold increase in STRA8 expression relative to vehicle-treated controls (p<0.05, n = 5; Figure 5A); revealing conserved induction of STRA8 expression by RA in the human fetal testis. No significant differences were found between RA- and vehicle treated cultures in the expression of SYCP3 (94.4±5.7% of controls, n.s; Figure 5B) or DMC1 (115.1±19.6% of controls, n.s.; Figure 5C) however, suggesting that whilst RA can selectively induce the expression of STRA8 in the human fetal testis, it may not be sufficient to induce additional meiosis-associated gene expression at this developmental stage, or in this experimental system.


Retinoic Acid signalling and the control of meiotic entry in the human fetal gonad.

Childs AJ, Cowan G, Kinnell HL, Anderson RA, Saunders PT - PLoS ONE (2011)

Retinoic acid promotes the expression of STRA8 but not other meiosis-associated genes in the second trimester human fetal testis.Human fetal testis (14–15 weeks gestation) were disaggregated to a single cell suspension and cultured in serum free medium in the presence of vehicle (DMSO) or 1 µM all trans retinoic acid (1 µM RA in DMSO) for 24 hours. RA treatment induced a 2.2±0.3 fold increase in the expression of STRA8 (A) relative to vehicle treated controls (a vs b, p<0.05, n = 5), indicating that RA-regulated expression of this gene is conserved in human fetal gonads. No significant differences in the expression of meiosis markers SYCP3 (B, n.s. n = 6) or DMC1 (C, n = 6, n.s.) were detected between RA- and vehicle-treated cultures, indicating that whilst RA can stimulate STRA8 expression, it is not sufficient to cause widespread activation of the meiosis-associated gene expression programme. Values denote mean ± s.e.m..
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3108594&req=5

pone-0020249-g005: Retinoic acid promotes the expression of STRA8 but not other meiosis-associated genes in the second trimester human fetal testis.Human fetal testis (14–15 weeks gestation) were disaggregated to a single cell suspension and cultured in serum free medium in the presence of vehicle (DMSO) or 1 µM all trans retinoic acid (1 µM RA in DMSO) for 24 hours. RA treatment induced a 2.2±0.3 fold increase in the expression of STRA8 (A) relative to vehicle treated controls (a vs b, p<0.05, n = 5), indicating that RA-regulated expression of this gene is conserved in human fetal gonads. No significant differences in the expression of meiosis markers SYCP3 (B, n.s. n = 6) or DMC1 (C, n = 6, n.s.) were detected between RA- and vehicle-treated cultures, indicating that whilst RA can stimulate STRA8 expression, it is not sufficient to cause widespread activation of the meiosis-associated gene expression programme. Values denote mean ± s.e.m..
Mentions: To determine whether the induction of STRA8 expression by RA is conserved between mouse and human, we investigated the effects of RA treatment on cells from the second trimester human fetal testis. To ensure germ cell exposure to RA, fetal testes (14–15 weeks gestational age, n = 6) were disaggregated to a single cell suspension (thus uncoupling germ cells from their associated somatic cells which are in the mouse thought to be the site of CYP26B1 expression) and cultured in serum free medium in the presence of either vehicle (DMSO) or 1 µM all-trans RA for 24 hours. Expression of STRA8, and of the meiosis markers SYCP3 and DMC1 was then assessed by qRT-PCR in control and RA-treated cultures. Treatment with RA for 24 hours resulted in a 2.2±0.3 fold increase in STRA8 expression relative to vehicle-treated controls (p<0.05, n = 5; Figure 5A); revealing conserved induction of STRA8 expression by RA in the human fetal testis. No significant differences were found between RA- and vehicle treated cultures in the expression of SYCP3 (94.4±5.7% of controls, n.s; Figure 5B) or DMC1 (115.1±19.6% of controls, n.s.; Figure 5C) however, suggesting that whilst RA can selectively induce the expression of STRA8 in the human fetal testis, it may not be sufficient to induce additional meiosis-associated gene expression at this developmental stage, or in this experimental system.

Bottom Line: The development of mammalian fetal germ cells along oogenic or spermatogenic fate trajectories is dictated by signals from the surrounding gonadal environment.Aspects of this model are hard to reconcile with the spatiotemporal pattern of germ cell differentiation in the human fetal ovary, however.We have therefore examined the expression of components of the RA synthesis, metabolism and signalling pathways, and their downstream effectors and inhibitors in germ cells around the time of the initiation of meiosis in the human fetal gonad.

View Article: PubMed Central - PubMed

Affiliation: Medical Research Council Human Reproductive Sciences Unit, The Queen's Medical Research Institute, University of Edinburgh, Edinburgh, United Kingdom. a.childs@ed.ac.uk

ABSTRACT
The development of mammalian fetal germ cells along oogenic or spermatogenic fate trajectories is dictated by signals from the surrounding gonadal environment. Germ cells in the fetal testis enter mitotic arrest, whilst those in the fetal ovary undergo sex-specific entry into meiosis, the initiation of which is thought to be mediated by selective exposure of fetal ovarian germ cells to mesonephros-derived retinoic acid (RA). Aspects of this model are hard to reconcile with the spatiotemporal pattern of germ cell differentiation in the human fetal ovary, however. We have therefore examined the expression of components of the RA synthesis, metabolism and signalling pathways, and their downstream effectors and inhibitors in germ cells around the time of the initiation of meiosis in the human fetal gonad. Expression of the three RA-synthesising enzymes, ALDH1A1, 2 and 3 in the fetal ovary and testis was equal to or greater than that in the mesonephros at 8-9 weeks gestation, indicating an intrinsic capacity within the gonad to synthesise RA. Using immunohistochemistry to detect RA receptors RARα, β and RXRα, we find germ cells to be the predominant target of RA signalling in the fetal human ovary, but also reveal widespread receptor nuclear localization indicative of signalling in the testis, suggesting that human fetal testicular germ cells are not efficiently shielded from RA by the action of the RA-metabolising enzyme CYP26B1. Consistent with this, expression of CYP26B1 was greater in the human fetal ovary than testis, although the sexually-dimorphic expression patterns of the germ cell-intrinsic regulators of meiotic initiation, STRA8 and NANOS2, appear conserved. Finally, we demonstrate that RA induces a two-fold increase in STRA8 expression in cultures of human fetal testis, but is not sufficient to cause widespread meiosis-associated gene expression. Together, these data indicate that while local production of RA within the fetal ovary may be important in regulating the onset of meiosis in the human fetal ovary, mechanisms other than CYP26B1-mediated metabolism of RA may exist to inhibit the entry of germ cells into meiosis in the human fetal testis.

Show MeSH
Related in: MedlinePlus