EXISTENCE OF MULTIPLE VITELLOGENIN GENE IN THE SHRIMP Fennerpenaeus merguiensis: EVIDENCE FOR GENE EXPANSION AND FUNCTION DIVERSIFICATION

Abstract: Vitellogenin (Vg) is the precursor of egg yolk proteins providing nutrients during early embryonic development.  Information related to shrimp vitellogenesis is important for us to understanding the mechanism of reproduction in shrimp aquaculture.  In this study, 3 Vg genes (FmVg1, FmVg2, FmVg3) were identified from the banana shrimp Fennerpenaeus merguiensis .   The cDNA of FmVg1, FmVg2 and FmVg3 ranged from 7758-7764 bp , and the encoded protein consisted of 2553-2585 amino acids. The genomic structure of FmVg1, FmVg2 and FmVg3 were highly 35conserved, containing 15 exons and 14 introns . Protein sequence alignment showed that the identity between FmVg1-FmVg2, FmVg1-FmVg3 and FmVg2-FmVg3 was 52.25%, 60.77% and 3756.45%, respectively.  Phylogenetic analysis further revealed that 'FmVg1' class vitellogenins seemed to be more conservative among shrimp, as these genes were clustered in a small branch separated from the 'FmVg2 and FmVg3' class vitellogenins . The expression patterns of FmVg1, FmVg2 and FmVg3 were similar in the hepatopancreas at different ovarian developmental stages, while the expression patterns between FmVg1 and FmVg2/3 in the ovary were remarkably different.  During ontogenic development, expression of these Vg genes all reached the highest levels at the post larvae stage. The three Vg genes also exhibited dynamic expression changes at different molting stages, with the highest expression level detected at the inter-molt stage. Taken together, our study provided evidence that at least three copies of the Vg gene are present in the banana shrimp. These Vg genes are potentially involved in ovary maturation and larval development, and the divergence in their sequences, structures and expression dynamics may reflects their functional diversification in shrimp.

Keywords: Fenneropenaeus merguiensis , vitellogenin, reproduction, genes, shrimp