A fundamental goal in developmental biology is to understand how distinct cell types containing the same genetic information arise from a common precursor cell. Sex determination is a key process that results in a unidirectional commitment of initially bipotential cells towards either the male or female fate, making it a unique model to study cell fate commitment and differentiation in vivo. Despite several decades of research, it is still unclear how epigenetic regulation is integrated with transcription factor binding to induce gene activation and repression during cell fate decisions. We found that epigenetic mechanisms contribute to the bipotential state of the fetal gonad and to the regulation of chromatin accessibility during and immediately downstream of the primary sex-determining switch. We generated an epigenetic profile of the supporting cell lineage of the gonad before and after sex determination, and showed that a number of sex-determining genes are bivalent at the bipotential stage, marked with both active H3K4me3 and repressive H3K27me3 histone modifications. We found that activation of the male or female pathway is accompanied by a drastic loss of H3K27me3 at male- or female-determining genes, respectively. In contrast, repressed genes that promote the alternate pathway remain bivalent even into adult life. There are two H3K27me3-specific histone demethylases: Kdm6b, which is autosomal and expressed at similar levels in both XX and XY cells, and Utx (Kdm6a), which escapes X- inactivation and is expressed at higher levels in females than in males. Utx is one of few genes that escape inactivation in both mice and humans, suggesting an evolutionarily-conserved dose-dependent function. Although Utx has a homolog on the Y- chromosome (Uty), studies suggest that it is catalytically inactive and functions through H3K27me3-independent mechanisms. We will investigate the hypothesis that Utx and/or Kdm6b is involved in establishing male of female fate through analysis of mutant mice. Given the potential to link sex chromosomes to sex determination, and/or to demonstrate an evolutionary link to the recently discovered role of Kdm6b in reptile sex determination, there is a high likelihood that this work will result in an important publication in the field. It will also advance training of the post-doctoral fellow (Sara Alexandra Garcia-Moreno) in enhancer/promoter interactions and their integration with epigenetic marks, bioinformatics, immunofluorescent imaging, the analysis of mouse mutants, and other career skills in preparation for the next step in her trajectory toward becoming an independent research scientist.

Public Health Relevance

Despite several decades of research, it is still unclear how epigenetic regulation is integrated with transcription factor binding to induce gene activation and repression during cell fate decisions. Mutations of several chromatin-remodeling proteins cause Disorders of Sexual Development, suggesting a critical role for chromatin remodeling in sex determination. This project will advance our understanding of the role of histone demethylases during the cell fate decisions in the bipotential gonad that drive sex determination, and explore the question of whether the sex chromosome dosage of the histone demethylase UTX plays a role in this process. !

National Institute of Health (NIH)
Eunice Kennedy Shriver National Institute of Child Health & Human Development (NICHD)
Method to Extend Research in Time (MERIT) Award (R37)
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Special Emphasis Panel (NSS)
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Taymans, Susan
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Duke University
Anatomy/Cell Biology
Schools of Medicine
United States
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Garcia-Moreno, S Alexandra; Plebanek, Michael P; Capel, Blanche (2018) Epigenetic regulation of male fate commitment from an initially bipotential system. Mol Cell Endocrinol 468:19-30
Maatouk, Danielle M; Natarajan, Anirudh; Shibata, Yoichiro et al. (2017) Genome-wide identification of regulatory elements in Sertoli cells. Development 144:720-730
Lin, Yi-Tzu; Barske, Lindsey; DeFalco, Tony et al. (2017) Numb regulates somatic cell lineage commitment during early gonadogenesis in mice. Development 144:1607-1618
Capel, Blanche (2017) Vertebrate sex determination: evolutionary plasticity of a fundamental switch. Nat Rev Genet 18:675-689
Bunce, Corey; Capel, Blanche (2016) Cycling in the Cell Fate Landscape. Curr Top Dev Biol 116:153-65
DeFalco, Tony; Bhattacharya, Indrashis; Williams, Alyna V et al. (2014) Yolk-sac-derived macrophages regulate fetal testis vascularization and morphogenesis. Proc Natl Acad Sci U S A 111:E2384-93
Capel, Blanche (2014) Development. The minimalist Y. Science 343:32-3
Capel, Blanche (2014) Ovarian epithelium regeneration by Lgr5(+) cells. Nat Cell Biol 16:743-4
Shaffer, H Bradley; Minx, Patrick; Warren, Daniel E et al. (2013) The western painted turtle genome, a model for the evolution of extreme physiological adaptations in a slowly evolving lineage. Genome Biol 14:R28
Capel, Blanche; Tanaka, Minoru (2013) Forward to the special issue on sex determination. Dev Dyn 242:303-6

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