Long-Range Regulation of Key Sex Determination Genes

The development of sexually dimorphic gonads is a unique process that starts with the specification of the bipotential genital ridges and culminates with the development of fully differentiated ovaries and testes in females and males, respectively. Research on sex determination has been mostly focused on the identification of sex determination genes, the majority of which encode for proteins and specifically transcription factors such as SOX9 in the testes and FOXL2 in the ovaries. Our understanding of which factors may be critical for sex determination have benefited from the study of human disorders of sex development (DSD) and animal models, such as the mouse and the goat, as these often replicate the same phenotypes observed in humans when mutations or chromosomic rearrangements arise in protein-coding genes. Despite the advances made so far in explaining the role of key factors such as SRY, SOX9, and FOXL2 and the genes they control, what may regulate these factors upstream is not entirely understood, often resulting in the inability to correctly diagnose DSD patients. The role of non-coding DNA, which represents 98% of the human genome, in sex determination has only recently begun to be fully appreciated. In this review, we summarize the current knowledge on the long-range regulation of 2 important sex determination genes, SOX9 and FOXL2, and discuss the challenges that lie ahead and the many avenues of research yet to be explored in the sex determination field.