OOCYTE DEVELOPMENT AND INCORPORATION OF H 3 -THYMIDINE AND HMJRIDINE IN PECTINARIA (CISTENIDES) GOULDII KENYON S. TWEEDELL Department of Biology, University of Notre Dame, Notre Dame, Indiana 46556, and the Marine Biological Laboratory, Woods Hole, Massachusetts 02543 Transformation from the oogonium and development of the primary oocyte involves intricate morphological and metabolic changes in the cell. Among these are enlargement of the germinal vesicle, development of the nucleolus and cyto-plasmic growth (Raven, 1961). It is generally believed that the necessary pre-meiotic changes in the nucleus precede these phenomena. Most evidence indicates that H 3 -thymidine is not incorporated into the germinal vesicle of the mature oocyte (Ficq, 1961a; Favard-Sereno and Durand, 1963b; Ficq, Aiello and Scarano, 1963) although recently Holland and Giese (1965) report that both the oogonia and the pre-leptotene primary oocytes of the sea urchin synthesize DNA within the ovary. These results imply that the synthesis of DNA needed for subsequent growth and maturation of the oocytes must occur after the last oogonial division and no later than the early premeiotic changes in the oocyte nucleus. Since there is evidence that various types of eggs have vast reserves of cyto-plasmic DNA (Bieber et al, 1959) or deoxyribosides (Hoff-J0rgensen and Zeuthen, 1952) and some indication of cytoplasmic uptake (Ficq, 1961a; Gintsburg, 1963) of H 3 -thymidine into the oocytes, the question arises, is the entire cyto-plasmic reserve acquired at the time of nuclear DNA synthesis or is it augmented throughout development of the oocyte? It is pertinent to determine whether the developing and growing oocyte is metabolically stable or if it is able to actively increase its DNA reserve. The continuous presentation of a specifically labeled nucleoside, H 3 -thymidine, in vivo is one approach to this problem. In contrast, the uptake of RNA precursors into the maturing oocyte appears to be widespread during oogenesis. In the starfish, H 3 -uridine uptake is localized in the nucleus, nucleolus (Ficq, 1961b) and cytoplasm (Geuskens, 1963), in the nucleus and nucleolus of the sea urchin oocyte (Ficq, Aiello and Scarano, 1963) and the nuclear sap, chromosomes and cytoplasm of the cricket oocyte (Favard-Sereno and Durand, 1963a). The use of H 3 -uridine and other precursors in conjunction with various inhibitors implicates the synthesis of at least three types of RNA (m-RNA, r-RNA and t-RNA) during maturation of the starfish and sea urchin oocyte (Ficq, 1961a; 1962; 1964). Since both the nucleolus and nucleus in Pectinaria increase in size and activity as the oocyte develops (Tweedell, 1962), a study of the incorporation of labeled uridine into the RNA of the nucleolus and nucleus seemed promising (Tweedell. 1964). 516
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