A histochemical study of oogenesis in the sea urchin, Strongylocentrotus purpuratus.

Abstract

1. Oogenesis in the sea urchin Strongylocentrotus purpuratus was studied by histological methods and by histochemical techniques for polysaccharides, lipids, and nucleic acids. Urchins were collected at Yaquina Head, Oregon at regular intervals between April 1966 and March 1967. An attempt was made to correlate seasonal variations in coastal water temperature with the gonadal cycle.2. Oogonia can be found throughout the year in small groups scattered along the walls of the ovary, but are most numerous in the late spring and early summer when the ovary is spent. The oocytes start growing in the late summer and early fall when the accessory cells start filling with lipid and polysaccharide globules. At this time the accessory cells are found to have inclusions that appear to be degenerate sex cells. The oocytes continue to grow through the late fall and early winter and their cytoplasm fills with lipid and polysaccharide. As the ova mature they move from the wall to the central portion of the acinus where they displace the accessory cells that had formerly been there.3. The ova that have been shed or are about to be shed contain pyroninophilic RNA which is not found in the cytoplasm of the oocytes. However, both ova and oocytes have RNA that is stainable with azure B. The pyroninophilic RNA is also found in accessory cells.4. Since all the oocytes do not mature at the same time, a sea urchin is able to shed many times during the breeding season which lasts from late December to early April. During this period the accessory cells progressively lose their globules. When the accessory cells are finally depleted of their lipid and polysaccharide, the oocytes no longer grow and the ovaries are spent.