YOLK PROTEIN-CHANGES DURING OOCYTE GROWTH IN EUROPEAN SEA BASS DICENTRARCHUS-LABRAX L

Oocyte growth within the follicle is due to the accumulation of the no rmal cytoplasmic components, and the endocytosis of hepatic derived pr otein, the vitellogenins. Vitellogenesis started in 200 mum oocytes; d uring oocyte growth the yolk globules increased in number and size. Yo lk globule morphology varies during oocyte growth: first they appear u niform and dense; then, in 500 mum oocytes they often appear to be div ided into 2 or 3 dense masses. Yolk proteins of pre-maturational oocyt es at different stages were compared with those of ovulated eggs by SD S gel electrophoresis. The largest components stained by Coomassie blu e and those stained by Stains-all, which had formed during vitellogene sis, either disappeared or diminished, while smaller components appear ed. The changes in yolk protein banding patterns during oocyte maturat ion are suggestive of extensive secondary proteolysis of yolk proteins ; such secondary proteolysis may generate, as in other marine teleosts , part of the osmotic gradient associated with the resumption of oocyt e meiotic maturation, before ovulation.