Cytochalasin-D retards sperm incorporation deep into the egg cytoplasm but not membrane fusion with the egg plasma membrane.
The fertilization process is impaired when spermatozoa are previously incubated with Cytochalasin-D (Cyt-D). Although this fact reveals the participation of polymerized actin in fertilization, the specific event obstructed by Cyt-D treatment has not been determined. To identify this event, we capacitated guinea pig spermatozoa in minimal capacitating medium with pyruvate and lactate (MCM-PL) with Cyt-D, to inseminate hamster zona pellucida (ZP)-free eggs. Cyt-D (70 microM) decreased F-actin relative concentration in capacitated spermatozoa to a larger extent than in spermatozoa incubated under control conditions. Cyt-D also cancelled the F-actin increase normally observed in acrosome-reacted cells, and decreased the number of these cells with normal F-actin localization at the equatorial zone. Insemination of eggs with Cyt-D treated spermatozoa did not change early fertilization events such as the egg cortical reaction (CR), membranes fusion, and egg F-actin new localization, but clearly retarded, by 16 hr, spermatozoa incorporation deep into the egg cytoplasm, and decondensation of egg metaphase II chromosomes. These results show that actin polymerization is necessary for spermatozoa incorporation deep into the egg cytoplasm, but not for plasma membrane fusion nor egg activation early steps.
Sánchez-Gutiérrez
Manuel
M
Departamento de Biología Celular, Centro de Investigacón y de Estudios Avanzados del Instituto Politécnico Nacional, Apdo Postal 14 740, México, DF.
Contreras
Rubén G
RG
Mújica
Adela
A
D020101:Acrosome Reaction; D000199:Actins / Q000378:metabolism; D000818:Animals; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D006224:Cricetinae; D015638:Cytochalasin D / Q000494:pharmacology*; D003593:Cytoplasm / Q000187:drug effects* / Q000648:ultrastructure; D005260:Female; D006168:Guinea Pigs; D007314:Insemination; D008297:Male; D008561:Membrane Fusion / Q000187:drug effects*; D008562:Membrane Glycoproteins / Q000378:metabolism; D018613:Microscopy, Confocal; D008854:Microscopy, Electron; D009865:Oocytes / Q000166:cytology* / Q000187:drug effects / Q000648:ultrastructure; D013075:Sperm Capacitation; D013084:Sperm-Ovum Interactions / Q000187:drug effects*; D013094:Spermatozoa / Q000187:drug effects* / Q000648:ultrastructure; D013997:Time Factors
D000199:Actins; D008562:Membrane Glycoproteins; D015638:Cytochalasin D