Poster Presentation ANZSCDB National Scientific Meeting 2019

Defining the role of FGF9 dimerization in mammalian testicular development (#Poster 19)

Anthony D Bird 1 2 , Brittany M Croft 1 2 3 , Masayo Harada 4 , Lingyun Tang 5 , Stefan Bagheri-Fam 6 , Makoto Ono 1 , Liang Zhou 7 , Peter Koopman 7 , Zhugang Wang 5 , Akita Keiichi 4 , Vincent Harley 1 2
  1. Hudson Institute of Medical Research, Clayton, VIC, Australia
  2. Department of Molecular and Translational Science, Monash University, Melbourne, Victoria, Australia
  3. Murdoch Childrens Research Institute, Parkville, VIC, Australia
  4. Tokyo Medical and Dental University, Tokyo, Japan
  5. State Key Laboratory of Medical Genomics, Research Center for Experimental Medicine, Rui-Jin Hospital, Shanghai Jiao Tong University School of Medicine (SJTUSM), Shanghai, P.R. China
  6. Department of Anatomy and Neuroscience, The University of Melbourne, Melbourne, VIC, Australia
  7. Institute for Molecular Bioscience, The University of Queensland, Brisbane, QLD, Australia

Unique among the wider Fibroblast Growth Factor (FGF) family, the FGF9 subfamily (FGF9, 16 and 20) is capable of reversible homodimerization, which serves as an auto-regulatory mechanism for FGF bioactivity. Although dimers diffusing through tissues are more favourably bound by heparin sulphate proteoglycan (HSPG) cofactors in the ECM, only FGF monomers can bind and activate cognate FGF receptors (FGFRs). Within this subfamily, FGF9 plays a crucial role during embryonic development of multiple tissues including in the testes, where loss of Fgf9 in chromosomally male (XY) mice causes male-to-female sex reversal. However, whether dimer formation regulates FGF9 function distinct from FGFR binding capability during testis development remains unexplored. Here, we investigated testicular development in missense mouse Fgf9 mutants which disrupt either FGF9 dimer formation (Fgf9D195N), FGF9-FGFR-binding (Fgf9S99N) or both (Fgf9N143T). At 12.5 days postcoitum (dpc), XY Fgf9S99N/S99N and XY Fgf9N143T/N143T fetal mouse gonads showed severely disorganised testis cords as shown by poor formation of SOX9-positive Sertoli cells into tubular structures. Both XY mutants also exhibited upregulation of the pro-ovarian factors FOXL2 and WNT4 at the gonadal poles, indicating partial XY sex reversal. In gonads from 12.5 dpc XY Fgf9D195N/D195N and also XY Fgf9D195N/- mice, the testicular phenotype was milder with evidence of disorganised testis cords and FOXL2 upregulation, though WNT4 was not detected. Thus, our findings indicate that homodimerization is required for FGF9-mediated testicular determination, though FGF9-FGFR binding plays a more critical role.