Induction of metaphase chromosome condensation in human sperm by Xenopus egg extracts

Cell-free extracts of Xenopus eggs cause permeabilized Xenopus sperm to form pronuclei, which condense into metaphase chromosomes when the cytosol from metaphase-arrested unfertilized eggs is added to the extracts. In this paper, the ability of these cell-free extracts to cause similar changes in permeabilized human sperm was examined. Sperm that had been treated with the disulfide reducing agent dithiothreitol formed pronuclei, whereas untreated sperm did not. The addition of metaphase cytosol to the extracts caused the pronuclei to form metaphase chromosomes but only after incubation times that were two to three times longer than those required for Xenopus sperm nuclei. These results indicate that despite species differences, the Xenopus egg extracts can be used to visualize the chromosomes of human sperm and possibly those of other species.