Birth of normal young after electrofusion of mouse oocytes with round spermatids.

Normally, round spermatids, the youngest male germ cells with a set of haploid chromosomes, cannot fertilize mature oocytes. However, when mouse spermatids were fused with oocytes, some of the resulting zygotes developed into normal fertile mice of either sex. This demonstrates that the nuclei of spermatids can provide the paternally imprinted chromosomes needed for full embryonic development and also that the complex postmeiotic modifications involved in sperm formation in the testis and their maturation in the epididymis merely serve to facilitate natural delivery of the paternal genome. This finding may find an application in the treatment of male infertility due to defective spermiogenesis/sperm maturation.