Intracytoplasmic sperm injection experiments using the mouse as a model

Due to the existence of ample background information on its reproduction, embryology and genetics, the mouse is potentially an excellent animal model for intracytoplasmic sperm injection (ICSI). Normal fertile mouse offspring have been obtained by ICSI using not only mature (epididymal) and immature (testicular) spermatozoa, but also round spermatids and secondary spermatocytes. This suggests that genomic imprinting of male germ cells is complete before spermiogenesis. Mature mouse spermatozoa carry one or more factors that activate oocytes, This sperm-borne oocyte-activating factor is present in testicular spermatozoa, but not in round spermatids. Thus, at feast in the mouse, it seems to appear (or become active) during spermiogenesis. Part of the factor seems to be associated with the perinuclear materials because, when freed from plasma and acrosomal membranes as well as all acrosome components, spermatozoa remain fully capable of activating oocytes by ICSI, Spermatozoa with grossly misshapen heads (e.g. those from the BALB/c mouse) are unable to fertilize oocytes under ordinary in-vivo and in-vitro conditions. However, by ICSI they can fertilize the oocytes, and the zygotes develop into fertile offspring. Inherently poorly motile spermatozoa (of male mice carrying two t haplotypes) are unable to fertilize, but through ICSI they can participate in normal fertilization and embryonic development, Examination of human sperm chromosomes after sperm injection into mouse oocytes revealed that spermatozoa with abnormal head morphology have a significantly higher incidence of chromosome abnormality than those with normal heads, yet the majority of the abnormal spermatozoa have normal chromosomal constitutions, These findings suggest that spermatozoa with aberrant morphology and/or motility are not necessarily genomically abnormal.