Poster Presentation 40th Annual Lorne Genome Conference 2019

Human and mouse FGF9 mutations affect male sex determination (#134)

Brittany Croft 1 2 , Anthony Bird 2 , Makoto Ono 2 3 , Stefanie Eggers 1 4 , Stefan Bagheri-Fam 2 , Janelle Ryan 2 , Patrick Western 5 , Andrew Kueh 6 , Elizabeth Thompson 7 , Tim Thomas 6 , Peter Stanton 2 , Masayo Harada 8 , Andrew Sinclair 9 , Vincent Harley 1
  1. Murdoch Childrens Research Institute , Melbourne, VIC, Australia
  2. Centre for Reproductive Health, Hudson Institute of Medical Research, Clayton, VIC, Australia
  3. Department of Paediatrics, Tokyo Bay Urayasu Ichikawa Medical Centre, Chiba, Japan
  4. Victorian Clinical Genetics Services, Royal Children's Hospital, Melbourne, VIC, Australia
  5. Centre for Genetic Diseases, Hudson Institute of Medical Research, Clayton, VIC, Australia
  6. Walter and Eliza Hall Institute of Medical Research,, Parkville, VIC, Australia
  7. SA Clinical Genetics Service, Women’s and Children’s Hospital, Adelaide, SA, Australia
  8. Department of Clinical Anatomy, Tokyo Medical and Dental University, Tokyo, Japan
  9. Murdoch Children's Research Institute, Melbourne, VIC, Australia

Disorders of Sex Development (DSDs) encompass a wide spectrum of conditions and often manifest with atypical gonads or genitalia. The majority of 46,XY DSD patients cannot be given an accurate diagnosis, which severely compromises their clinical management.

FGF9 is critical for the repression of pro-ovarian signalling pathways such as WNT4/RSPO1 and FOXL2. This ensures sufficient levels of SOX9 are expressed in the somatic cells of the embryonic gonad to drive Sertoli cell differentiation and ultimately, male testicular development. Loss of Fgf9 results in complete male to female sex reversal, while Fgf9 gene mutants impairing FGF9 homodimerization in humans and mice lead to skeletal defects such as synostosis.

Here we investigate the requirement of FGF9 dimer formation for testicular development, using homodimer-compromised FGF9 mutants from both mouse models and a human DSD patient.  

We examined two mouse mutants first the spontaneous mouse Fgf9 mutant; Elbow knee synostosis (Eks), amino acid substitution N143T, lies at the homodimerization interface and impairs FGF9 homodimerization. Second a model of patient mutation S99N in mice which reduce receptor binding. Examination of XY Fgf9N143T/N143T and Fgf9S99N/S99N gonads showed delayed testes cord development and ectopic expression of the female Granulosa cell marker FOXL2 at the gonadal poles, indicative of XY sex reversal.

We have further identified a 46,XY GD DSD patient with an amino acid substitution D195N, previous studies indicated that the D195 residue is critical for the homodimerization of FGF9. In vitro analysis showed D195N has a reduced ability to induce Sertoli cell proliferation, which is required for normal testis development. Fgf9D195N/null mice show mild sex reversal, potentially due to the loss of FGF9-FGF9 interactions.

Our results suggest that FGF9 homodimerization and receptor binding are required for FGF9 function during testis development. A disruption in one or both of these pathways causes sex reversal.