Glial cell line-derived neurotrophic factor (GDNF) is essential for colonization and expansion of turbot (Scophthalmus maximus) spermatogonia stem cells in recipient and in vitro culture

Germ cell transplantation (GCT) is a promising biotechnology producing donor-derived gametes in surrogate recipients. It plays a critical role of protecting endangered species, propagation of elite species with desired traits as well as long-term preservation of genetic resources in combination with cryopreservation. However, GCT often fails because of the low colonization rate even complete loss of donor cells in recipients. Glial cell line-derived neurotrophic factor (GDNF) is necessary for self-renew of mammals spermatogonia stem cells (SSCs), and it also contributes to the proliferation of SSCs in vitro culture in some animals. In turbot ( Scophthalmus maximus ), we found that the expressions of gdnf and gfrα1a were predominantly observed in spermatogonia rather than somatic cells, which differed from their expression patterns in mammals. The efficiency of exogenous spermatogonia transplantation in Japanese flounder ( Paralichthys olivaceus ) larvae could be substantially enhanced by incubating donor cells from turbot with 100ng/ml GDNF prior to transplantation, resulting in a notable rise in colonization rate from 33%-50% to 61.5%. Besides, the addition of 20ng/ml GDNF in cell medium could also promote the proliferation of turbot SSCs in vitro. These results demonstrated the gdnf in turbot testis expression characteristics and suggested that addition of GNDF might be an effective way to improve the GCT efficiency and promote the SSCs expansion in vitro culture.