Limits...
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.

Show MeSH

Related in: MedlinePlus

Conserved and divergent patterns of expression of STRA8, CYP26B1 and NANOS1-3 in the human fetal gonad.qRT-PCR analysis of human fetal gonads reveals female-biased and developmentally-regulated expression of STRA8 (A). STRA8 expression increased significantly between 8–9 and 14–16 weeks in the human fetal ovary (a vs b, p<0.05) consistent with the initiation of meiosis in the fetal ovary around 11 weeks gestation. Levels of transcripts encoding STRA8 were low and not significantly different between human fetal testes and ovaries at 8–9 weeks gestation, but were significantly higher in fetal ovaries than fetal testes at 14–16 weeks (c vs d, p<0.0001) and 17–20 weeks (e vs f, p = 0.008). CYP26B1 (B) expression was not significantly different between samples of the same sex at different gestational ages, but was significantly higher at in the fetal ovary than the fetal testis at 14–16 weeks (a vs b, p = 0.02); suggesting the male-specific expression of CYP26B1 reported in mice at a comparable developmental stage is not conserved to humans. NANOS2 (C) expression was predominantly male-specific and developmentally-regulated, with expression increasing in the human fetal testis with increasing gestational age (a,b,c, p<0.001). NANOS2 expression was also significantly higher in fetal testes than ovaries at 14–16 weeks (d vs e, p = 0.01) and 17–20 weeks (f vs g, p<0.01), a result consistent with a role for this protein in repressing meiosis in the fetal male germline. 8–9, 14–16 and 17–20 denote gestation age (in weeks) of specimens. No differences were detected in the expression of NANOS1 (D) between testis and ovaries at any gestational age, nor between gonads of the same sex at any developmental stage. NANOS3 expression (E) was significantly higher in the human fetal ovary at 14–16 weeks gestation than at 8–9 weeks gestation (a vs b, p<0.05), in contrast to the downregulation of the homologous gene in the fetal mouse ovary at the comparable developmental stage. Expression of NANOS3 was also greater in the fetal ovary than in the fetal testis at 14–16 weeks (c vs d, p<0.05) and 17–20 weeks (e vs f, p<0.02). 8–9, 14–16 and 17–20 denote the gestational age (in weeks) of specimens, values denote mean ± s.e.m, 8–9, 14–16 and 17–20 denote the gestational age (in weeks) of specimens.
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC3108594&req=5

pone-0020249-g004: Conserved and divergent patterns of expression of STRA8, CYP26B1 and NANOS1-3 in the human fetal gonad.qRT-PCR analysis of human fetal gonads reveals female-biased and developmentally-regulated expression of STRA8 (A). STRA8 expression increased significantly between 8–9 and 14–16 weeks in the human fetal ovary (a vs b, p<0.05) consistent with the initiation of meiosis in the fetal ovary around 11 weeks gestation. Levels of transcripts encoding STRA8 were low and not significantly different between human fetal testes and ovaries at 8–9 weeks gestation, but were significantly higher in fetal ovaries than fetal testes at 14–16 weeks (c vs d, p<0.0001) and 17–20 weeks (e vs f, p = 0.008). CYP26B1 (B) expression was not significantly different between samples of the same sex at different gestational ages, but was significantly higher at in the fetal ovary than the fetal testis at 14–16 weeks (a vs b, p = 0.02); suggesting the male-specific expression of CYP26B1 reported in mice at a comparable developmental stage is not conserved to humans. NANOS2 (C) expression was predominantly male-specific and developmentally-regulated, with expression increasing in the human fetal testis with increasing gestational age (a,b,c, p<0.001). NANOS2 expression was also significantly higher in fetal testes than ovaries at 14–16 weeks (d vs e, p = 0.01) and 17–20 weeks (f vs g, p<0.01), a result consistent with a role for this protein in repressing meiosis in the fetal male germline. 8–9, 14–16 and 17–20 denote gestation age (in weeks) of specimens. No differences were detected in the expression of NANOS1 (D) between testis and ovaries at any gestational age, nor between gonads of the same sex at any developmental stage. NANOS3 expression (E) was significantly higher in the human fetal ovary at 14–16 weeks gestation than at 8–9 weeks gestation (a vs b, p<0.05), in contrast to the downregulation of the homologous gene in the fetal mouse ovary at the comparable developmental stage. Expression of NANOS3 was also greater in the fetal ovary than in the fetal testis at 14–16 weeks (c vs d, p<0.05) and 17–20 weeks (e vs f, p<0.02). 8–9, 14–16 and 17–20 denote the gestational age (in weeks) of specimens, values denote mean ± s.e.m, 8–9, 14–16 and 17–20 denote the gestational age (in weeks) of specimens.

Mentions: Expression of STRA8 was low/absent in the gonads of both sexes at 8–9 weeks gestation (Figure 4A), consistent with these tissues containing only pre-meiotic proliferating germ cells at this developmental stage. STRA8 expression increased significantly between 8–9 and 14–16 weeks in the human fetal ovary however (p<0.05), concomitant with the initiation of meiosis in this tissue. STRA8 expression remained very low in the testis at all gestations examined, and was significantly higher in the fetal ovary than testis at 14–16 weeks (p<0.0001) and 17–20 weeks (p<0.008) gestation. The developmental and sex-specific pattern of Stra8 expression therefore appears to be conserved between the fetal gonads of humans and mice at comparable developmental stages, as reported previously [18], [20].


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)

Conserved and divergent patterns of expression of STRA8, CYP26B1 and NANOS1-3 in the human fetal gonad.qRT-PCR analysis of human fetal gonads reveals female-biased and developmentally-regulated expression of STRA8 (A). STRA8 expression increased significantly between 8–9 and 14–16 weeks in the human fetal ovary (a vs b, p<0.05) consistent with the initiation of meiosis in the fetal ovary around 11 weeks gestation. Levels of transcripts encoding STRA8 were low and not significantly different between human fetal testes and ovaries at 8–9 weeks gestation, but were significantly higher in fetal ovaries than fetal testes at 14–16 weeks (c vs d, p<0.0001) and 17–20 weeks (e vs f, p = 0.008). CYP26B1 (B) expression was not significantly different between samples of the same sex at different gestational ages, but was significantly higher at in the fetal ovary than the fetal testis at 14–16 weeks (a vs b, p = 0.02); suggesting the male-specific expression of CYP26B1 reported in mice at a comparable developmental stage is not conserved to humans. NANOS2 (C) expression was predominantly male-specific and developmentally-regulated, with expression increasing in the human fetal testis with increasing gestational age (a,b,c, p<0.001). NANOS2 expression was also significantly higher in fetal testes than ovaries at 14–16 weeks (d vs e, p = 0.01) and 17–20 weeks (f vs g, p<0.01), a result consistent with a role for this protein in repressing meiosis in the fetal male germline. 8–9, 14–16 and 17–20 denote gestation age (in weeks) of specimens. No differences were detected in the expression of NANOS1 (D) between testis and ovaries at any gestational age, nor between gonads of the same sex at any developmental stage. NANOS3 expression (E) was significantly higher in the human fetal ovary at 14–16 weeks gestation than at 8–9 weeks gestation (a vs b, p<0.05), in contrast to the downregulation of the homologous gene in the fetal mouse ovary at the comparable developmental stage. Expression of NANOS3 was also greater in the fetal ovary than in the fetal testis at 14–16 weeks (c vs d, p<0.05) and 17–20 weeks (e vs f, p<0.02). 8–9, 14–16 and 17–20 denote the gestational age (in weeks) of specimens, values denote mean ± s.e.m, 8–9, 14–16 and 17–20 denote the gestational age (in weeks) of specimens.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3108594&req=5

pone-0020249-g004: Conserved and divergent patterns of expression of STRA8, CYP26B1 and NANOS1-3 in the human fetal gonad.qRT-PCR analysis of human fetal gonads reveals female-biased and developmentally-regulated expression of STRA8 (A). STRA8 expression increased significantly between 8–9 and 14–16 weeks in the human fetal ovary (a vs b, p<0.05) consistent with the initiation of meiosis in the fetal ovary around 11 weeks gestation. Levels of transcripts encoding STRA8 were low and not significantly different between human fetal testes and ovaries at 8–9 weeks gestation, but were significantly higher in fetal ovaries than fetal testes at 14–16 weeks (c vs d, p<0.0001) and 17–20 weeks (e vs f, p = 0.008). CYP26B1 (B) expression was not significantly different between samples of the same sex at different gestational ages, but was significantly higher at in the fetal ovary than the fetal testis at 14–16 weeks (a vs b, p = 0.02); suggesting the male-specific expression of CYP26B1 reported in mice at a comparable developmental stage is not conserved to humans. NANOS2 (C) expression was predominantly male-specific and developmentally-regulated, with expression increasing in the human fetal testis with increasing gestational age (a,b,c, p<0.001). NANOS2 expression was also significantly higher in fetal testes than ovaries at 14–16 weeks (d vs e, p = 0.01) and 17–20 weeks (f vs g, p<0.01), a result consistent with a role for this protein in repressing meiosis in the fetal male germline. 8–9, 14–16 and 17–20 denote gestation age (in weeks) of specimens. No differences were detected in the expression of NANOS1 (D) between testis and ovaries at any gestational age, nor between gonads of the same sex at any developmental stage. NANOS3 expression (E) was significantly higher in the human fetal ovary at 14–16 weeks gestation than at 8–9 weeks gestation (a vs b, p<0.05), in contrast to the downregulation of the homologous gene in the fetal mouse ovary at the comparable developmental stage. Expression of NANOS3 was also greater in the fetal ovary than in the fetal testis at 14–16 weeks (c vs d, p<0.05) and 17–20 weeks (e vs f, p<0.02). 8–9, 14–16 and 17–20 denote the gestational age (in weeks) of specimens, values denote mean ± s.e.m, 8–9, 14–16 and 17–20 denote the gestational age (in weeks) of specimens.
Mentions: Expression of STRA8 was low/absent in the gonads of both sexes at 8–9 weeks gestation (Figure 4A), consistent with these tissues containing only pre-meiotic proliferating germ cells at this developmental stage. STRA8 expression increased significantly between 8–9 and 14–16 weeks in the human fetal ovary however (p<0.05), concomitant with the initiation of meiosis in this tissue. STRA8 expression remained very low in the testis at all gestations examined, and was significantly higher in the fetal ovary than testis at 14–16 weeks (p<0.0001) and 17–20 weeks (p<0.008) gestation. The developmental and sex-specific pattern of Stra8 expression therefore appears to be conserved between the fetal gonads of humans and mice at comparable developmental stages, as reported previously [18], [20].

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