INTRACYTOPLASMIC SPERM INJECTION EXPERIMENTS USING THE MOUSE AS A MODEL

Due to the existence of ample background information on its reproducti on, embryology and genetics, the mouse is potentially an excellent ani mal model for intracytoplasmic sperm injection (ICSI). Normal fertile mouse offspring have been obtained by ICSI using not only mature (epid idymal) and immature (testicular) spermatozoa, but also round spermati ds and secondary spermatocytes. This suggests that genomic imprinting of male germ cells is complete before spermiogenesis. Mature mouse spe rmatozoa carry one or more factors that activate oocytes, This sperm-b orne oocyte-activating factor is present in testicular spermatozoa, bu t not in round spermatids. Thus, at feast in the mouse, it seems to ap pear (or become active) during spermiogenesis. Part of the factor seem s 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, Sper matozoa 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 z ygotes develop into fertile offspring. Inherently poorly motile sperma tozoa (of male mice carrying two t haplotypes) are unable to fertilize , but through ICSI they can participate in normal fertilization and em bryonic development, Examination of human sperm chromosomes after sper m injection into mouse oocytes revealed that spermatozoa with abnormal head morphology have a significantly higher incidence of chromosome a bnormality than those with normal heads, yet the majority of the abnor mal spermatozoa have normal chromosomal constitutions, These findings suggest that spermatozoa with aberrant morphology and/or motility are not necessarily genomically abnormal.