Molecular alteration of three forms of vitellogenins and their product yolk proteins during oocyte growth and maturation in grey mullet (Mugil cephalus)
Seven yolk proteins (YPs) derived from three distinct types of vitellogenin (VgA, VgB, and VgC) were purified from the vitellogenic ovaries of grey mullet (Mugil cephalus). Three YPs appeared to be VgA derivatives and were designated as lipovitellin A (LvA), b’-component A (b’-cA), and LvA-phosvitin A complex (LvA-PvA). In ovulated eggs, these VgA derivatives were mostly degraded. Three other YPs (LvB, b’-cB, and PvB) appeared to be VgB derivatives. In eggs, b’-cB, and PvB were hardly detected, while LvB remained as a large peptide with a slight decrease in mass. One YP component (LvC) appeared to be a VgC derivative that underwent no alteration in native mass but was proteolytically nicked during oocyte maturation. The maturation-associated proteolysis of mullet YPs is similar to that which we have reported for other marine teleosts spawning pelagic eggs, supporting the significance of Vg multiplicity to reproductive physiology in this group of fishes.