Quantitative changes in yolk protein and other components in the ovary and testis of the sea urchin Pseudocentrotus depressus.

Both male and female sea urchins accumulate the major yolk protein (MYP; the most abundant yolk granule protein in sea urchin eggs) in the nutritive phagocytes of immature gonads before gametogenesis. In this study, quantitative changes in MYP as well as in other biochemical components in the ovary and testis were examined in the course of gametogenesis in Pseudocentrotus depressus. Before gametogenesis, both the ovary and testis contained large quantities of proteins, lipids and polysaccharides. MYP reached about 80% of total protein in both sexes. In the testis, MYP decreased rapidly as spermatogenesis proceeded, and the fully mature testis contained little MYP; the levels of lipids and polysaccharides also decreased. In contrast, the levels of nucleic acids and proteins other than MYP increased markedly. In the ovary, MYP decreased gradually as oogenesis proceeded, and the fully mature ovary contained less than half of the initial amount of MYP. Polysaccharides also decreased, whereas proteins other than MYP increased. These results, taken together with those from other studies, suggest that MYP serves as a protein reserve that accumulates before gametogenesis and is used as material for synthesizing new substances constituting gametes in both male and female sea urchins.