Both Gfrα1a and 1b are involved in the self-renewal and maintenance of spermatogonial stem cells in medaka

Glial cell-derived neurotrophic factor family receptor alpha-1 (GFRα1) plays a crucial role in the self-renewal and maintenance of spermatogonial stem cells (SSCs) from mammals. However, to date, our knowledge about its role in fish SSCs is limited. In the present study, the medaka (Oryzias latipes) gfrα1 duplicate genes, Olgfrα1a and Olgfrα1b, were cloned and characterized. Furthermore, their expression profile and biological activity were investigated. OlGfrα1a and OlGfrα1b contain 524 and 466 amino acid residues, respectively. Both are orthologous to mammalian Gfrα1 by sequence analyses and appear high in spermatogonia by in situ hybridization assay. The knockdown of OlGfrα1a and/or OlGfrα1b via vivo-morpholino oligos significantly inhibited the self-renewal and maintenance of SSCs, as evidenced by the decreased proliferation activity of SG3 cells (a spermatogonial stem cell line derived from adult medaka testis) as well as spermatogonia in the testicular organ culture, the decreased survival rate and expression levels of pluripotency-related genes (klf4, lin28b, bcl6b and etv5) in SG3 cells. Additionally, our study indicates that OlGfrα1a might function by binding either Gdnfa or b (the two medaka Gdnf homologs), whilst OlGfrα1b by binding Gdnfa not b. Taken together, our study indicates that both OlGfrα1a and 1b are involved in the self-renewal and maintenance of SSCs by binding Gdnfa and/or b, respectively. These findings suggest that the GDNF/ GFRα1 signaling pathway might be conserved from mammals to fish species.