Changes in the protein components of vitelline envelope during oogenesis of a tubiculous polychaete, Schizobranchia insignis.

In sabellid polychaetes the vitelline envelopes, in which microvilli with glycocalyx structures at the tips are invested, change in structure during oogenesis. Vitelline envelopes isolated from Schizobranchia oocytes 25-100 micron and 160-185 micron in diameter, were analyzed in protein components by iodination, electrophoresis, Western blotting and radioactive labeling technique. The observations demonstrate that the membrane proteins of the vitelline envelopes are not consistent but variable in components during oogenesis. Most of these proteins, particularly the high molecular weight proteins, are PAS-positive glycoproteins, which may have specific carbohydrate residues binding to wheat germ agglutinin. The proteins could be labeled with [3H]valine within 36 h by incubating the whole oocytes in sea water to a high level, indicating that the proteins are actively synthesized by the growing oocytes. Synthetic rates of the proteins differ from each other at one stage and are higher in the small than in the large oocytes in general, suggesting that the membrane proteins are involved in the function of the vitelline envelopes during oogenesis.