Multiple vitellogenin‐derived yolk proteins in gray mullet (Mugil cephalus): Disparate proteolytic patterns associated with ovarian follicle maturation

Abstract

Disparate proteolytic patterns of yolk proteins, derived from three types of vitellogenin (VgA, VgB, and VgC), were observed in gray mullet. Immuno-biochemical analyses of extracts obtained from vitellogenic ovaries (VO) and ovulated eggs (OE) confirmed that a large proportion of VgA-derived lipovitellin (LvA) was degraded into free amino acids (FAAs) during ovarian follicle maturation. The maturation-associated alteration of VgB-derived Lv (LvB) involved only limited proteolysis; the heavy and light LvB chains were dissociated into at least three and one polypeptide fragments, respectively. The native mass of VgC-derived Lv (LvC) exhibited little difference between VO and OE, although it was apparent that the LvC was 'nicked' during maturation, resulting in the appearance of several bands in OE. Similar analyses confirmed that VgA-derived beta'-component (beta'-cA) and VgB-derived beta'-c (beta'-cB) decreased during maturation in both quantity and native mass, while phosvitin derived from either VgA (PvA) or VgB (PvB) appeared to be degraded into FAAs. The pattern of maturation-associated proteolysis of mullet yolk proteins is similar to that reported for other marine teleosts spawning pelagic eggs. However, the depository ratio of the three distinct types of Lv in the mullet VO appeared to be different from that estimated for another marine pelagophil, the barfin flounder. These results support a recent paradigm regarding the significance of Vg multiplicity upon successive physiological events in this group of fishes including the hydration of maturing oocytes, the acquisition of proper egg buoyancy, and the generation of requisite nutrient stocks for each stage of embryogenesis and larval development.

Vitellogenesis and choriogenesis in fishes

“…Vtg subtypes has been developed, establishing an assessment system that fully considers the 'multiple Vtg model' mentioned above [118]. Furthermore, in red lip mullet, we established identification and measurement systems for major Vtg subtypes and confirmed estrogen responsiveness.…”

“…This is particularly true for Salmonidae. In addition, in fish species where the complete form of Vtg has been further classified into VtgAa and VtgAb, the ratio of subtypes present in the blood depends on each species [117,118]. Because of the large molecular weight differences, the ratio of complete to incomplete forms of Vtg can be readily determined by electrophoresis and similar methods.…”

“…Our recent research on the physiological functions of each type of Vtg during oocyte maturation and embryogenesis following fertilization suggested that egg quality is directly dependent on the relative abundance (accumulation ratio) of each Vtg within the ovulated eggs [117,118]. Assuming that this hypothesis is correct, when EEDCs disrupt the ratios of different forms of Vtgs found in the blood or accumulated in the egg, this suggests a potential direct impact on fertilization or survival rates.…”

Egg protein bound amino acid content and embryo/larva success in common dentex (Dentex dentex), a marine pelagophil teleost

“…This outcome is reasonable because it has been shown that the quantitative ratio of VtgAa versus VtgAb in post-vitellogenic oocytes may possibly control the yield of FAAs (e.g., see Amano et al, 2008a).…”

Phospho-Signaling at Oocyte Maturation and Fertilization: Set Up for Embryogenesis and Beyond Part II. Kinase Regulators and Substrates

“…lipovitellin/phosvitin were described during oocyte maturation and early embryos in various species, e.g. barfin flounder, Verasper moseri, a marine teleost (Matsubara et al 1999;Sawaguchi et al 2006), red seabream (Pagrus major), another marine teleost and gray mullet (Mugil cephalus) (Amano et al 2008). A substrate pp25 for protein serine/threonine kinases was derived from the precursor of pp43 that is consisting of a portion of the Xenopus VgB1 protein (Xi et al 2003).…”