Oral Presentation ESA-SRB-NZSE-CaSR 2026 in conjunction with ENSA

Utilising a Dhx37 conditional knockout mouse model to elucidate mechanisms for 46,XY DSD  (144887)

Sarah C Moody 1 , Kenneth McElreavey 2 , Anu Bashamboo 2 , Serge Nef 1
  1. Department of Genetic Medicine and Development, University of Geneva, Genveva, Switzerland
  2. Department of Developmental and Stem Cell Biology, Unit of Human Developmental Genetics, Institut Pasteur, Université Paris Cité, Paris, France

Background
Differences in sex development (DSDs) affects approximately 1:5,000 live births. In 46,XY DSD with gonadal dysgenesis (incidence ~1:100,000), the genetic cause remains unknown in ~50% of cases. DHX37, a ubiquitously expressed RNA helicase involved in ribosome biogenesis, is one of the most frequently mutated genes in 46,XY gonadal dysgenesis and testicular regression syndrome, accounting for ~10% of cases. However, its role in testis development is unknown.

Methods
We generated Dhx37lox/lox;Rosa26-tdTomatoki/ki mice, crossed with Nr5a1-Cre+/Tg mice to delete Dhx37 and activate the tdTomato reporter in Nr5a1-expressing somatic cells. Control (Dhx37lox/lox,Dhx37+/lox), heterozygous (Dhx37+/lox;Nr5a1-Cre+/Tg) and conditional knockout (cKO; Dhx37lox/lox;Nr5a1-Cre+/Tg) males were analysed at embryonic day (E)16.5 and postnatal days (P)0, P10 and P20 (n=3-10/genotype/age). Body and testis weights and anogenital distance index (AGDi) were measured postnatally. Testes and adrenals at all ages were fixed for histological analyses (H&E, immunostaining).

Results
Dhx37 cKO mice exhibited smaller adrenal glands from E16.5 and reduced body weights at P20 (0.77-fold of controls). Gross testis morphology appeared normal at E16.5 with progressive reduction in size postnatally, with significantly lower testis:body weight in cKOs at P10 (0.36-fold) and P20 (0.26-fold) compared with controls. AGDi was significantly lower in cKO at P20 (0.83-fold). Testis cord diameter was transiently increased in P0 cKO testes (1.3-fold of controls). At P10, primary spermatocytes were present in all genotypes with preserved testis tubule morphology, although cKO testes contained more proliferative Sertoli (PCNA+;SOX9+) cells. By P20, cKO testes had enlarged tubule lumens with thin epithelium and germ cell arrest at the pachytene stage, whereas controls contained normal tubules with round spermatids.

Conclusion
Loss of Dhx37 in testicular somatic cells did not result in a sex reversal phenotype, however postnatal testicular regression occurred. Further analysis is required to elucidate the function of Dhx37 in the testis and how loss of function causes 46,XY DSD.