In vitro maturation of Arbacia punctulata oocytes and initiation of heavy body formation

Summary An ultrastructural study of in vitro maturation of A. punctulata oocytes was undertaken to determine when heavy body formation was initiated. No heavy bodies were seen in germinal vesicle oocytes or in oocytes undergoing germinal vesicle breakdown or polar body formation. Heavy bodies were only observed in ova examined one to two hours after pronuclear formation. Several small heavy bodies were seen in sections of eggs fixed as early as three hours after the pronucleus had formed. The number of these structures in the egg cytoplasm increased with time. Therefore it is concluded that heavy body formation in sea urchin ova is a phenomenon following nuclear maturation.Contribution No. 222 from the Institute for Molecular and Cellular Evolution. Supported in part by grants from the National Institutes of Health (5-T01-HD00026-09 to the Fertilization and Gamete Physiology Training Program at the Marine Biological Laboratory and predoctoral fellowship 1-F01-GM-36,719-01A1 to C. M. Conway) and the National Science Foundation (GB3899 to C. B. Metz).The authors are grateful to Drs. A. F. Conway, Giovanni Giudice, and Gertrude W. Hinsch for consultation and criticism of this work.