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Sperm nuclear transformations in cytoplasmic extracts from surf clam (Spisula solidissima) oocytes
F J Longo1, L Mathews, R E Palazzo
1Department of Anatomy, University of Iowa, Iowa City 52252.
Developmental Biology
|March 1, 1994
Summary
Sperm nuclei (SN) in surf clams expand and decondense in vitro when exposed to oocyte extracts after germinal vesicle breakdown (GVBD). This process mimics in vivo fertilization events, with nuclear envelope assembly occurring later.
Area of Science:
- Developmental Biology
- Reproductive Biology
- Cell Biology
Background:
- Sperm nuclei (SN) in surf clams undergo significant morphological transformations post-fertilization, including expansion, condensation, and enlargement into male pronuclei.
- These SN changes are temporally linked to maternal chromatin events like germinal vesicle breakdown (GVBD) and meiotic maturation.
Purpose of the Study:
- To investigate the in vitro effects of surf clam oocyte extracts on sperm nuclei (SN) following parthenogenetic activation.
- To analyze the capacity of oocyte extracts to induce SN decondensation and nuclear envelope assembly, mimicking fertilization events.
Main Methods:
- Surf clam oocytes were parthenogenetically activated, and extracts were prepared at different time points (unactivated, 4, 15, 65 min postactivation).
- Sperm heads were incubated in these extracts for up to 5 hours, followed by ultrastructural examination and anti-lamin antibody staining.
- Inhibitors (EDTA, 2,6-dimethylaminopurine, histone, protamine) were used to block SN decondensation.
Main Results:
- Oocyte extracts from 15 min postactivation induced SN expansion in 90% of cases, resembling in vivo chromatin decondensation.
- SN incubated in post-GVBD extracts showed decondensed chromatin and variable membranous cisternae; nuclear envelope assembly was absent.
- Extracts from 65 min postactivation (postmeiotic) promoted SN decondensation and the formation of an intact nuclear envelope reactive to anti-lamin.
Conclusions:
- Oocyte extracts can induce sperm nuclei (SN) decondensation and nuclear envelope formation in vitro, mirroring in vivo fertilization processes.
- The timing of extract preparation (post-GVBD vs. postmeiotic) dictates the extent of SN decondensation and nuclear envelope assembly.
- Specific inhibitors block SN decondensation, suggesting key molecular players are involved in these early fertilization events.