A site-specific, single-copy transgenesis strategy to identify 5' regulatory sequences of the mouse testis-determining gene Sry

Identification of regulatory elements required for Stra8 expression in fetal ovarian germ cells of the mouse

In mice, the entry of germ cells into meiosis crucially depends on the expression of stimulated by retinoic acid gene 8 (Stra8). Stra8 is expressed specifically in pre-meiotic germ cells of females and males, at fetal and postnatal stages, respectively, but the mechanistic details of its spatiotemporal regulation are yet to be defined. In particular, there has been considerable debate regarding whether retinoic acid is required, in vivo, to initiate Stra8 expression in the mouse fetal ovary. We show that the distinctive anterior-to-posterior pattern of Stra8 initiation, characteristic of germ cells in the fetal ovary, is faithfully recapitulated when 2.9 kb of the Stra8 promoter is used to drive eGFP expression. Using in vitro transfection assays of cutdown and mutant constructs, we identified two functional retinoic acid responsive elements (RAREs) within this 2.9 kb regulatory element. We also show that the transcription factor DMRT1 enhances Stra8 expression, but only in the presence of RA and the most proximal RARE. Finally, we used CRISPR/Cas9-mediated targeted mutation studies to demonstrate that both RAREs are required for optimal Stra8 expression levels in vivo.

Role of epigenetic regulation in mammalian sex determination

Mammalian sex determination is triggered by activation of the mammalian sex-determining gene, Sry, in a spatially and temporally controlled manner. Because reduced or delayed Sry expression results in male-to-female sex reversal, male development is highly dependent on the accurate transcription of Sry. SRY dysregulation is a potential cause of human disorders of sex development (DSD). In addition to changes in DNA sequences, gene expression is regulated by epigenetic mechanisms. Epigenetic regulation ensures spatial and temporal accuracy of the expression of developmentally regulated genes. Epigenetic regulation such as histone tail modification, DNA methylation, chromatin remodeling, and non-coding RNA regulation engages several biological processes in multicellular organisms. In recent years, it has been revealed that various types of epigenetic regulation are involved in accurate gonadal differentiation in mammals. In particular, histone modification plays an integral part in sex determination, which is the first step of gonadal differentiation. Here, we focus on the findings on the epigenetic modifications that regulate Sry expression. Finally, we discuss the role of metabolism that potentially alters the epigenetic state in response to environmental cues.

Two genes substitute for the mouse Y chromosome for spermatogenesis and reproduction

The mammalian Y chromosome is considered a symbol of maleness, as it encodes a gene driving male sex determination, Sry, as well as a battery of other genes important for male reproduction. We previously demonstrated in the mouse that successful assisted reproduction can be achieved when the Y gene contribution is limited to only two genes, Sry and spermatogonial proliferation factor Eif2s3y. Here, we replaced Sry by transgenic activation of its downstream target Sox9, and Eif2s3y, by transgenic overexpression of its X chromosome-encoded homolog Eif2s3x. The resulting males with no Y chromosome genes produced haploid male gametes and sired offspring after assisted reproduction. Our findings support the existence of functional redundancy between the Y chromosome genes and their homologs encoded on other chromosomes.