Expression and cellular localization of insulin-like growth factor 3 in gonads of the seasonal breeding teleost silver pomfret ( Pampus argenteus )

Insulin-like growth factor 3 plays an important role in gonad development in teleost fish. Previous studies found that igf3 was specifically expressed in gonads of silver pomfret ( Pampus argenteus ). Unlike in other fish, IGF3 is a membrane protein in silver pomfret, and its specific role in gonads is unclear. Herein, we explored the importance of IGF3 in oogenesis and spermatogenesis in silver pomfret by analyzing gene expression and cellular localization. During follicular development, igf3 was detected in ovaries at both mRNA and protein levels during the critical stages of vitellogenesis (IV–VI). Localization analysis detected igf3 mRNA and protein in somatic cells, including theca and granulosa cells around oocytes. Similar to cathepsin L and cathepsin K , igf3 was consistently expressed in ovaries during vitellogenesis, suggesting that it might play a key role in vitellogenesis of oocytes. During spermatogenesis, igf3 mRNA and protein levels were high in stages II, IV, and V, similar to sycp3 and dmc1 , and the highest igf3 mRNA and protein levels were reached in stage VI. Furthermore, igf3 mRNA and protein were detected in spermatogonia, spermatocytes, spermatids, and surrounding Sertoli cells, but not in spermatozoon, indicating that IGF3 might be involved in differentiation and meiosis of spermatogonia.