Disorders of sex development (DSDs) include 46,XY gonadal dysgenesis (GD), where a specific molecular diagnosis is made in only ~30% of patients. Improved understanding of the genetic causes of DSD will lead to better diagnosis and management.
FGF9 is expressed in Sertoli cells and is critical for testis determination in the mouse since Fgf9-/- mice show XY gonadal sex reversal. In the developing XY gonad FGF9 maintains Sox9 expression through repression of Wnt4. However, the mechanism of Wnt4 repression by FGF9 is still unknown. We have established an in vitro assay system of FGF9 function during foetal gonadal development to identify the signalling pathways involved in Wnt4 repression. We show that FGF9 treatment of the mouse Sertoli cell line 15P-1 can efficiently down-regulate Wnt4 expression in a dose dependent manner. Cycloheximide treatment inhibited Wnt4 repression, suggesting that FGF9 requires new protein synthesis to down-regulate Wnt4. FGF signalling activates four major signalling pathways; MAP Kinase, AKT, STAT, and the PLCĪ³. To determine which pathways are involved in FGF9 repression of Wnt4, we treated 15P-1 cells with drugs to these pathways. Drugs blocking the ERK1/2 and JNK pathways significantly inhibited Wnt4 repression, suggesting that FGF9 down-regulates Wnt4 via the ERK1/2 and JNK MAPK pathways, but not via p38 MAPK pathway. Testing in gonad cultures ex vivo is underway.
FGF9 mutation has not been described in human DSD. Here, we identified an FGF9 variant in a 46,XY GD patient, a maternally-derived heterozygous single nucleotide substitution, c.583G>A (p.Asp195Asn) using 1000 DSD gene targeted Massively Parallel Sequencing. Recombinant wildtype and the variant FGF9 protein have been purified and the variant protein showed lower affinity for heparin biochemically. In vitro Wnt4 repression assay and ex vivo experiments are underway. CRISPR/Cas9 knock-in mice of the variant Fgf9 are also being produced and analysed.