[The visualization of the pronuclei in zygotes of the American mink]

Visualization of the pronuclei in optically nontransparent mink zygotes was achieved after centrifugation at 15,000 g. Under these conditions, the lipid fraction was concentrated in the light hemisphere of the zygote, while the pronuclei were localized in the equatorial area. Centrifugation did not affect the viability of zygotes, and no reliable differences in the rate of birth were found after transplantation of the native and centrifuge zygotes to the recipient females. Treatment of the zygotes with cytochalasin B before centrifugation leads to the condensation of lipids in the light area and allows distinct visualization of the pronuclei in the free zone. However, when these zygotes are cultivated, cleavage is irregular. Organization of the cytoskeleton in the mink zygotes is discussed.