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Retinoic Acid Receptors Control Spermatogonia Cell-Fate and Induce Expression of the SALL4A Transcription Factor.

Gely-Pernot A, Raverdeau M, Teletin M, Vernet N, Féret B, Klopfenstein M, Dennefeld C, Davidson I, Benoit G, Mark M, Ghyselinck NB - PLoS Genet. (2015)

Bottom Line: We also show that ATRA activates RAR and RXR bound to a conserved regulatory region to increase expression of the SALL4A transcription factor in spermatogonia.Our results reveal that this major pluripotency gene is a target of ATRA signaling and that RAR/RXR heterodimers are the functional units driving its expression in spermatogonia.They add to the mechanisms through which ATRA promote expression of the KIT tyrosine kinase receptor to trigger a critical step in spermatogonia differentiation.

View Article: PubMed Central - PubMed

Affiliation: Institut de Génétique et de Biologie Moléculaire et Cellulaire (IGBMC), Département de Génétique Fonctionnelle et Cancer, Illkirch, France; Centre National de la Recherche Scientifique (CNRS), UMR7104, Illkirch, France; Institut National de la Santé et de la Recherche Médicale (INSERM), U964, Illkirch, France; Université de Strasbourg (UNISTRA), Illkirch Cedex, France.

ABSTRACT
All-trans retinoic acid (ATRA) is instrumental to male germ cell differentiation, but its mechanism of action remains elusive. To address this question, we have analyzed the phenotypes of mice lacking, in spermatogonia, all rexinoid receptors (RXRA, RXRB and RXRG) or all ATRA receptors (RARA, RARB and RARG). We demonstrate that the combined ablation of RXRA and RXRB in spermatogonia recapitulates the set of defects observed both upon ablation of RAR in spermatogonia. We also show that ATRA activates RAR and RXR bound to a conserved regulatory region to increase expression of the SALL4A transcription factor in spermatogonia. Our results reveal that this major pluripotency gene is a target of ATRA signaling and that RAR/RXR heterodimers are the functional units driving its expression in spermatogonia. They add to the mechanisms through which ATRA promote expression of the KIT tyrosine kinase receptor to trigger a critical step in spermatogonia differentiation. Importantly, they indicate also that meiosis eventually occurs in the absence of a RAR/RXR pathway within germ cells and suggest that instructing this process is either ATRA-independent or requires an ATRA signal originating from Sertoli cells.

No MeSH data available.


Related in: MedlinePlus

Proposed model for the regulation of Kit expression by ATRA during the transition from Aal to A1 spermatogonia.(A) Spermatogonia at an undifferentiated state. ATRA is not available to activate RARG/RXRA heterodimer and transcription of Sall4 is low. Transcription of Kit is also low because ZBTB16 is bound to its promoter [48]. In addition, translation of Kit mRNA already present in cells [2,49,50] is prevented by the Mirc1, Mirc3 and miR221/222 small interfering RNAs (brown comb) [50,51]. (B) Spermatogonia at a differentiating state upon ATRA action. (i) At the Aal-A1 transition, one possible way for ATRA (yellow triangle) to regulate Kit expression is to activate RARG/RXRA heterodimer, which increases Sall4a expression (high, our study). (ii) SALL4A in large amount can then sequesters ZBTB16 [14], clearing Kit promoter and relieving the repression of Kit transcription normally exerted by ZBTB16 [48]. (iii) ATRA is also proposed to increase the level of SOHLH1, which can replace ZBTB16 on regulatory regions to increase Kit expression (high) [52]. Sohlh1 is however not a direct target of RARG as RAR-binding sites are not found in this gene [34] and its expression is not induced by BMS961 (our study). (iv) Alternatively, SALL4A can also interact with DNMT3A/B to facilitate the epigenetic shift required for A1 differentiation [42,43]. (v) In parallel, ATRA can further induce KIT protein through decreasing expression of microRNA such as Mirc1, Mirc3 and miR221/222 that prevent Kit mRNA translation. How ATRA regulate miRNA expression is however unknown, as RARE have not been identified in the vicinity of their promoters [34,50,51]. ATRA can also function as a rapid, non-genomic, agent by (vi) increasing the loading of Kit mRNA on polysomes (grey ovals) and its translation [41] and (vii) inducing phosphorylation of KIT (orange stars) and of downstream KIT-effectors, reinforcing commitment towards the A1 spermatogonia fate [53].
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pgen.1005501.g008: Proposed model for the regulation of Kit expression by ATRA during the transition from Aal to A1 spermatogonia.(A) Spermatogonia at an undifferentiated state. ATRA is not available to activate RARG/RXRA heterodimer and transcription of Sall4 is low. Transcription of Kit is also low because ZBTB16 is bound to its promoter [48]. In addition, translation of Kit mRNA already present in cells [2,49,50] is prevented by the Mirc1, Mirc3 and miR221/222 small interfering RNAs (brown comb) [50,51]. (B) Spermatogonia at a differentiating state upon ATRA action. (i) At the Aal-A1 transition, one possible way for ATRA (yellow triangle) to regulate Kit expression is to activate RARG/RXRA heterodimer, which increases Sall4a expression (high, our study). (ii) SALL4A in large amount can then sequesters ZBTB16 [14], clearing Kit promoter and relieving the repression of Kit transcription normally exerted by ZBTB16 [48]. (iii) ATRA is also proposed to increase the level of SOHLH1, which can replace ZBTB16 on regulatory regions to increase Kit expression (high) [52]. Sohlh1 is however not a direct target of RARG as RAR-binding sites are not found in this gene [34] and its expression is not induced by BMS961 (our study). (iv) Alternatively, SALL4A can also interact with DNMT3A/B to facilitate the epigenetic shift required for A1 differentiation [42,43]. (v) In parallel, ATRA can further induce KIT protein through decreasing expression of microRNA such as Mirc1, Mirc3 and miR221/222 that prevent Kit mRNA translation. How ATRA regulate miRNA expression is however unknown, as RARE have not been identified in the vicinity of their promoters [34,50,51]. ATRA can also function as a rapid, non-genomic, agent by (vi) increasing the loading of Kit mRNA on polysomes (grey ovals) and its translation [41] and (vii) inducing phosphorylation of KIT (orange stars) and of downstream KIT-effectors, reinforcing commitment towards the A1 spermatogonia fate [53].

Mentions: A comprehensive model summarizing the combination of transcriptional, post-transcriptional and non-genomic effects of ATRA pathways possibly controlling KIT expression and the commitment of Aal spermatogonia towards the A1 fate is proposed (Fig 8). The interest of better understanding the control of KIT expression in spermatogonia is not restricted to gametogenesis, but extends to testicular cancer. In fact, seminoma cells frequently bear somatic mutations activating KIT, or overexpress KIT or SALL4 [7,44,45]. Therefore, pharmacological modulation of mechanisms that regulate KIT expression in spermatogonia, such as antagonizing ATRA action, might have important applications for future therapeutic strategies.


Retinoic Acid Receptors Control Spermatogonia Cell-Fate and Induce Expression of the SALL4A Transcription Factor.

Gely-Pernot A, Raverdeau M, Teletin M, Vernet N, Féret B, Klopfenstein M, Dennefeld C, Davidson I, Benoit G, Mark M, Ghyselinck NB - PLoS Genet. (2015)

Proposed model for the regulation of Kit expression by ATRA during the transition from Aal to A1 spermatogonia.(A) Spermatogonia at an undifferentiated state. ATRA is not available to activate RARG/RXRA heterodimer and transcription of Sall4 is low. Transcription of Kit is also low because ZBTB16 is bound to its promoter [48]. In addition, translation of Kit mRNA already present in cells [2,49,50] is prevented by the Mirc1, Mirc3 and miR221/222 small interfering RNAs (brown comb) [50,51]. (B) Spermatogonia at a differentiating state upon ATRA action. (i) At the Aal-A1 transition, one possible way for ATRA (yellow triangle) to regulate Kit expression is to activate RARG/RXRA heterodimer, which increases Sall4a expression (high, our study). (ii) SALL4A in large amount can then sequesters ZBTB16 [14], clearing Kit promoter and relieving the repression of Kit transcription normally exerted by ZBTB16 [48]. (iii) ATRA is also proposed to increase the level of SOHLH1, which can replace ZBTB16 on regulatory regions to increase Kit expression (high) [52]. Sohlh1 is however not a direct target of RARG as RAR-binding sites are not found in this gene [34] and its expression is not induced by BMS961 (our study). (iv) Alternatively, SALL4A can also interact with DNMT3A/B to facilitate the epigenetic shift required for A1 differentiation [42,43]. (v) In parallel, ATRA can further induce KIT protein through decreasing expression of microRNA such as Mirc1, Mirc3 and miR221/222 that prevent Kit mRNA translation. How ATRA regulate miRNA expression is however unknown, as RARE have not been identified in the vicinity of their promoters [34,50,51]. ATRA can also function as a rapid, non-genomic, agent by (vi) increasing the loading of Kit mRNA on polysomes (grey ovals) and its translation [41] and (vii) inducing phosphorylation of KIT (orange stars) and of downstream KIT-effectors, reinforcing commitment towards the A1 spermatogonia fate [53].
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4591280&req=5

pgen.1005501.g008: Proposed model for the regulation of Kit expression by ATRA during the transition from Aal to A1 spermatogonia.(A) Spermatogonia at an undifferentiated state. ATRA is not available to activate RARG/RXRA heterodimer and transcription of Sall4 is low. Transcription of Kit is also low because ZBTB16 is bound to its promoter [48]. In addition, translation of Kit mRNA already present in cells [2,49,50] is prevented by the Mirc1, Mirc3 and miR221/222 small interfering RNAs (brown comb) [50,51]. (B) Spermatogonia at a differentiating state upon ATRA action. (i) At the Aal-A1 transition, one possible way for ATRA (yellow triangle) to regulate Kit expression is to activate RARG/RXRA heterodimer, which increases Sall4a expression (high, our study). (ii) SALL4A in large amount can then sequesters ZBTB16 [14], clearing Kit promoter and relieving the repression of Kit transcription normally exerted by ZBTB16 [48]. (iii) ATRA is also proposed to increase the level of SOHLH1, which can replace ZBTB16 on regulatory regions to increase Kit expression (high) [52]. Sohlh1 is however not a direct target of RARG as RAR-binding sites are not found in this gene [34] and its expression is not induced by BMS961 (our study). (iv) Alternatively, SALL4A can also interact with DNMT3A/B to facilitate the epigenetic shift required for A1 differentiation [42,43]. (v) In parallel, ATRA can further induce KIT protein through decreasing expression of microRNA such as Mirc1, Mirc3 and miR221/222 that prevent Kit mRNA translation. How ATRA regulate miRNA expression is however unknown, as RARE have not been identified in the vicinity of their promoters [34,50,51]. ATRA can also function as a rapid, non-genomic, agent by (vi) increasing the loading of Kit mRNA on polysomes (grey ovals) and its translation [41] and (vii) inducing phosphorylation of KIT (orange stars) and of downstream KIT-effectors, reinforcing commitment towards the A1 spermatogonia fate [53].
Mentions: A comprehensive model summarizing the combination of transcriptional, post-transcriptional and non-genomic effects of ATRA pathways possibly controlling KIT expression and the commitment of Aal spermatogonia towards the A1 fate is proposed (Fig 8). The interest of better understanding the control of KIT expression in spermatogonia is not restricted to gametogenesis, but extends to testicular cancer. In fact, seminoma cells frequently bear somatic mutations activating KIT, or overexpress KIT or SALL4 [7,44,45]. Therefore, pharmacological modulation of mechanisms that regulate KIT expression in spermatogonia, such as antagonizing ATRA action, might have important applications for future therapeutic strategies.

Bottom Line: We also show that ATRA activates RAR and RXR bound to a conserved regulatory region to increase expression of the SALL4A transcription factor in spermatogonia.Our results reveal that this major pluripotency gene is a target of ATRA signaling and that RAR/RXR heterodimers are the functional units driving its expression in spermatogonia.They add to the mechanisms through which ATRA promote expression of the KIT tyrosine kinase receptor to trigger a critical step in spermatogonia differentiation.

View Article: PubMed Central - PubMed

Affiliation: Institut de Génétique et de Biologie Moléculaire et Cellulaire (IGBMC), Département de Génétique Fonctionnelle et Cancer, Illkirch, France; Centre National de la Recherche Scientifique (CNRS), UMR7104, Illkirch, France; Institut National de la Santé et de la Recherche Médicale (INSERM), U964, Illkirch, France; Université de Strasbourg (UNISTRA), Illkirch Cedex, France.

ABSTRACT
All-trans retinoic acid (ATRA) is instrumental to male germ cell differentiation, but its mechanism of action remains elusive. To address this question, we have analyzed the phenotypes of mice lacking, in spermatogonia, all rexinoid receptors (RXRA, RXRB and RXRG) or all ATRA receptors (RARA, RARB and RARG). We demonstrate that the combined ablation of RXRA and RXRB in spermatogonia recapitulates the set of defects observed both upon ablation of RAR in spermatogonia. We also show that ATRA activates RAR and RXR bound to a conserved regulatory region to increase expression of the SALL4A transcription factor in spermatogonia. Our results reveal that this major pluripotency gene is a target of ATRA signaling and that RAR/RXR heterodimers are the functional units driving its expression in spermatogonia. They add to the mechanisms through which ATRA promote expression of the KIT tyrosine kinase receptor to trigger a critical step in spermatogonia differentiation. Importantly, they indicate also that meiosis eventually occurs in the absence of a RAR/RXR pathway within germ cells and suggest that instructing this process is either ATRA-independent or requires an ATRA signal originating from Sertoli cells.

No MeSH data available.


Related in: MedlinePlus