Genomic disturbance of vitellogenin 2 (vtg2) leads to vitellin membrane deficiencies and significant mortalities at early stages of embryonic development in zebrafish (Danio rerio)

The specific functions and essentiality of type II vitellogenin (Vtg2) in early zebrafish development were investigated in this study. A vtg2-mutant zebrafish line was produced and effects of genomic disturbance were observed in F2 females and F3 offspring. No change in vtg2 transcript has been detected, however, Vtg2 abundance in F2 female liver was 5×, and in 1 hpf F3 vtg2-mutant embryos was 3.8× less than Wt (p < 0.05). Fecundity was unaffected while fertilization rate was more than halved in F2 vtg2-mutant females (p < 0.05). Hatching rate was significantly higher in F3 vtg2-mutant embryos in comparison to Wt embryos. Survival rate declined drastically to 29% and 18% at 24 hpf and 20 dpf, respectively, in F3 vtg2-mutant embryos. The introduced mutation caused vitelline membrane deficiencies, significant mortalities at early embryonic stages, and morphological abnormalities in the surviving F3 vtg2-mutant larvae. Overrepresentation of histones, zona pellucida proteins, lectins, and protein degradation related proteins in F3 vtg2-mutant embryos provide evidence to impaired mechanisms involved in vitellin membrane formation. Overall findings imply a potential function of Vtg2 in acquisition of vitellin membrane integrity, among other reproductive functions, and therefore, its essentiality in early zebrafish embryo development.