RNA Helicase function in vertebrate sex-determination and human Disorders of Sex Development (DSD) – RNA-SEX

Gonad development in mammals depends on a cell fate decision that occurs in a bipotential somatic cell to commit to Sertoli (male) or granulosa (female) cells. This is a classic but poorly understood process in biology. Data suggest that mammalian sex-determination (SD) involves complex and mutually antagonistic genetic pathways. SD is achieved by suppression of the alternate fate and maintained in adulthood by mutually antagonistic double-repressive pathway(s). This system serves as a paradigm for cell fate choice during development. Much of our understanding of SD comes from the analysis of individuals who are sex-reversed including XY females with gonadal dysgenesis.
These patients form a subgroup of Disorders/differences in Sex Development (DSD). Most of these cases are unexplained at a molecular level. Recently, we determined that 11 % of all patients who have 46,XY gonadal dysgenesis and 25% of patients with testicular regression syndrome are associated (p=10-10) with specific and usually de novo mutations in highly evolutionary conserved domains of the RNA helicase DHX37. This factor is known to be essential for the biogenesis of the small ribosome subunit in yeast and recent data suggests it has the same function in human cells. This is an entirely novel finding that does not integrate into any known factor/pathway involved in vertebrate sex-determination. Our preliminary data show that the gene is expressed specifically in somatic cells during testis-determination, is specifically up-regulated in an animal XX male-to-female sex-reversal model, and surprisingly the DHX37 protein is located on the nuclear membrane, rather than the nucleolus as would be expected for a ribosome biogenesis factor. The project`s objectives are to understand the role of the RNA helicase DHX37 in mammalian sex-determination and the pathophysiology of human Disorders of Sex Development (DSD) using multiple complimentary animal models, in vitro, ex-vivo and cellular reprogramming approaches using human and animal tissues/cells. We hypothesis that the DHX37 RNA helicase has acquired a novel role in vertebrate sex-determination. Specifically, we will determine if the DHX37-mediated sex-reversal a new human ribosomopathy by determining anomalies in pre-rRNA processing in cells from patients carrying pathogenic mutations. We will also determine functionally relevant protein and RNA-partners using a combination of established approaches and novel techniques using biomaterial from human and animal gonads during sex-determination. Burden analysis tests will determine if any of these factors contribute to DSD in large exome dataset of DSD patients. The ability of DHX37 to cause sex-reversal in a range of animal models will be determined and, if informative, used to study the physiopathology of the disease. Finally, the consequences of mutations will be studies in iPSC derived Sertoli-like cell models that we have developed, as well as gonad on-a-chip technologies.
This proposal has several major impacts. First, we identified a new genetic cause of DSD. Mutations in DHX37 are as common as mutations involving the SRY gene, so from a patient management and diagnostic perspective this is a major contribution in the field. Second, this proposal aims to understand how this RNA helicase interacts with the known pathways of vertebrate sex-determination and hence has a wider interest in the field of sex-determination and the cell fate choice decisions that are involved. Finally, our data strongly suggest that some forms of sex-reversal are a ribosomopathy. Understanding the mechanism(s) involved will have a much wider impact on the relationship between ribosome biogenesis and function and how specific disease phenotypes are seen in the known human ribosomopathies.