UCLA

Disorders of Sex Development (DSD) encompass a wide range of urogenital anomalies, ranging from mild hypospadias to sex reversal with genital ambiguity that occur in approximately 0.5-1% of live births. Despite the prevalence of DSD, the molecular mechanisms behind the transformation of the bipotential gonad into a testis or an ovary are not completely understood. In this thesis, we explore molecular mechanisms in mammalian sex determination using mouse and human models of sex development.

To identify novel genomic regions and genes in sex determination, we utilize a long- standing and powerful model in mammalian sex determination, the C57BL/6J (B6)-YPOS. None of the B6-YPOS animals have fully normal testis during embryonic development. Our approach utilizes a congenic strain in which a region of 129S1/SvIM (129) origin on chromosome 11 protects from B6-YPOS sex reversal (abbreviated as B6.129-YPOS). Using traditional mouse genetics and backcrossing, we narrowed the 50 megabase (Mb) congenic region to a protective two Mb interval containing only the promoter region of Sox9, a known male sex determination gene.

In order to facilitate a genetic diagnosis of patients with DSD, we developed a novel targeted diagnostic tool based on next generation sequencing technology to rapidly provide a genetic diagnosis in these patients. Using a single test, we can assess sex chromosome karyotype, copy number variation (CNV), and identify damaging single nucleotide variants (SNV) which may result in disease. We have validated our targeted sequencing approach in a pilot group of 14 patients with DSD. Currently, less than 20% of all patients with a DSD receive a definitive diagnosis, yet this type of comprehensive genetic test is critical to assigning appropriate treatment, predicting future development, and evaluating outcomes in this unique patient population.

The synergism between discoveries in mouse and human genetics has existed throughout the history of sex development research--with animal models informing human research, and vice versa. As genomic tools continue to exponentially increase the amount of data generated, this long and healthy relationship between human and mouse genetics will continue to elucidate the complex genetic regulation in sex determination.