Course of proteolytic cleavage in three classes of yolk proteins during oocyte maturation in barfin flounderVerasper moseri, a marine teleost spawning pelagic eggs
✍ Scribed by Matsubara, Takahiro; Koya, Yasunori
- Publisher
- John Wiley and Sons
- Year
- 1997
- Tongue
- English
- Weight
- 173 KB
- Volume
- 278
- Category
- Article
- ISSN
- 0022-104X
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✦ Synopsis
Proteolytic degradation of three classes of vitellogenin-derived yolk proteins (lipovitellin, phosvitin, and β´-component) was quantitatively examined during oocyte maturation in barfin flounder, Verasper moseri, a marine teleost which spawns pelagic eggs. Oocyte maturation takes place over 7 days at a water temperature of 6°C. Morphological changes in maturing oocytes, characterized by increasing size and transparency, occurred markedly during the latter half of oocyte maturation. Lipovitellin, which has a native molecular weight of 410,000 in postvitellogenic oocytes, was cleaved into 170,000 fragments after the fourth day of oocyte maturation. A quantitative immunological assay showed a decline of total intact lipovitellin content in maturing oocytes of about 74%, corresponding to maturation-associated alterations of its molecular structure. An additional class of yolk protein, β´-component, also decreased in abundance during the same period. Indirect quantification of phosvitin in egg yolk, done by measuring serine content in gel chromatography fractions, demonstrated rapid degradation of this protein from the fourth to fifth day of oocyte maturation. Quantitative analysis of free amino acids in maturing oocytes showed a reverse correlation between the amount of intact forms of these three classes of yolk proteins and the water content of oocytes. All three classes of yolk proteins clearly undergo proteolytic cleavage during the latter half of oocyte maturation, possibly to provide osmotic effectors for oocyte hydration, which increases egg buoyancy, and to ensure an available stock of nutrients usable for early development.