Sperm nuclear transformations consist of enlargement and condensation coordinate with stages of meiotic maturation in fertilized Spisula solidissima oocytes

Abstract

Rates of sperm nuclear expansion were measured and correlated with processing of the maternal chromatin in synchronous populations of fertilized surf clam ( Spisula solidissima) oocytes fixed at regular intervals following insemination and stained with the DNA fluorochrome Hoechst 33342. Sperm nuclei expanded in four distinct phases each temporally coordinate with events of meiotic maturation: germinal vesicle stage (phase A), germinal vesicle breakdown (phase B), polar body formation (phase C), and female pronuclear development (phase D). Sperm nuclei were essentially unchanged during phase A (rate = 0.1 μm 2/min, enlarged during phases B (rate = 8.2 μm 2/min) and D (rate = 6.2 μm 2/min), and condensed during phase C (rate = −1.9 μm 2/min). Sperm nuclear enlargement during phase D was significantly less in polyspermic and polygynic zygotes. The effects of various treatments (temperature, microtubule disruption, pH alterations, and metabolic and protein synthesis inhibitions) which perturbed sperm nuclear enlargement and meiotic processing of the maternal chromatin indicated that the two processes are coupled and may be linked by common regulatory agents.