| dc.description.abstract |
Mammalian oocytes microsurgically injected with spermatozoa can develop intonormal offspring. Apparently the oocyte has the ability to decompose oreliminate such sperm components as the plasma membrane and acrosomal contents,which normally do not enter its cytoplasm. Species in which normal offspringwere obtained by direct sperm injection include: human, mouse, rabbit, horse,sheep, cattle, pig, and monkey. In the mouse, normal offspring can also beobtained routinely by the injection of round spermatid nuclei into oocytes.This suggests that all post-meiotic modifications of spermatozoa(spermiogenesis, sperm maturation, capacitation and the acrosome reaction)evolved as processes solely dedicated to delivering male genomes into femalegametes. Birth of normal off-spring after injection of spermatocytes intomaturing or mature oocytes suggests that the mechanisms controlling meiosis ofmale and female germ cells are similar, if not the same. Spermatozoa do notneed to be morphologically normal or alive in the conventional sense toparticipate in embryo development; as long as they have intact genomes, theyare able to produce normal offspring. Chromosomes within the first and secondpolar bodies can be used as substitutes for female pronuclei for theproduction of normal offspring. The nuclei of adult somatic cells can be usedfor production of animals. This procedure, involving introduction of cellnuclei into enucleated oocytes (genomic cloning), is rather inefficient atpresent. Many obstacles must be overcome before it is accepted as a safe,novel method to reproduce scientifically, medically or economically valuableanimals. For human cloning the prime consideration must be the welfare of thechild. |
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