Amano Haruna, Fujita Toshiaki, Hiramatsu Naoshi, Kagawa Hirohiko, Matsubara Takahiro, Sullivan Craig V, Hara Akihiko
Faculty of Fisheries Sciences, Hokkaido University, Hakodate, Hokkaido, Japan.
Mol Reprod Dev. 2008 Aug;75(8):1307-17. doi: 10.1002/mrd.20864.
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.
在鲻鱼中观察到源自三种卵黄蛋白原（VgA、VgB和VgC）的卵黄蛋白的不同蛋白水解模式。对来自卵黄生成期卵巢（VO）和排卵卵（OE）的提取物进行免疫生化分析证实，在卵泡成熟过程中，很大一部分源自VgA的脂卵黄蛋白（LvA）被降解为游离氨基酸（FAA）。源自VgB的Lv（LvB）与成熟相关的变化仅涉及有限的蛋白水解；重链和轻链的LvB分别解离成至少三个和一个多肽片段。源自VgC的Lv（LvC）在VO和OE之间的天然质量几乎没有差异，尽管很明显LvC在成熟过程中被“切割”，导致OE中出现几条带。类似的分析证实，源自VgA的β'-组分（β'-cA）和源自VgB的β'-c（β'-cB）在成熟过程中数量和天然质量均下降，而源自VgA（PvA）或VgB（PvB）的卵黄高磷蛋白似乎被降解为FAA。鲻鱼卵黄蛋白与成熟相关的蛋白水解模式与其他产浮性卵的海洋硬骨鱼所报道的模式相似。然而，三种不同类型的Lv在鲻鱼VO中的沉积比例似乎与另一种海洋浮游性鱼类条石鲷的估计比例不同。这些结果支持了最近关于Vg多样性对这组鱼类连续生理事件重要性的范式，这些生理事件包括成熟卵母细胞的水合作用（卵黄生成）、获得适当的卵浮力以及为胚胎发育和幼体发育的每个阶段生成必需的营养储备。
