Changes in gene expression and cellular localization of insulin-like growth factor 3 in gonads of a seasonal breeding teleost, silver pomfret, Pampus argenteus

Abstract As a new member of IGFs, insulin-like growth factor 3 (igf3) plays an important role in the development of gonads of teleost fish. Previous studies have found that igf3 was specifically expressed in the gonads of silver pomfret (Pampus argenteus). Different with other fish, the igf3 protein of silver pomfret is a membrane protein, and its specific role in the gonads was not yet clear. Here, we further studied the importance of igf3 in oogenesis and spermatogenesis in silver pomfret by analyzing its gene expression and cellular localization. During follicular development, igf3 mRNA and protein were significantly expressed in ovaries stayed in the critical period of vitellogenesis (Ⅳ - Ⅵ). Localization studies found that igf3 mRNA and protein were significantly and obviously expressed in somatic cells including theca and granulosa cells around oocytes. Meanwhile, similar with cathepsin L and cathepsin K, igf3 had a high and consistent expression levels in ovaries during vitellogenesis, suggesting igf3 might play a key role in the process of vitellogenesis of oocytes. In the process of spermatogenesis, the expression of igf3 mRNA and protein were high in stages Ⅱ, Ⅳ and Ⅴ, which was similar with the expression of sycp3 and dmc1. And the highest expression level of igf3 mRNA and protein reached in stage Ⅵ. At the same time, positive signals of igf3 mRNA and protein were detected in spermatogonium, spermatocytes, spermatid and surrounding Sertoli cells, but not expressed on spermatozoon, which indicated that igf3 might be involved in the differentiation and meiosis of spermatogonium.