Development and chromosomal constitution of nuclear‐transplants derived from male germ cells

Nuclei of spermatogonial cells derived from juvenile and adult (Rana pipiens) were transplanted singly into enucleated eggs to determine whether germ cell nuclei are developmentally totipotent. Control nuclear transfers from undetermined somatic cells promoted genuine cleavage in 77% of the injected eggs and 54% of the complete blastulae derived from this series developed into normal larvae. In contrast to the control study, eggs transplanted with germ cell nuclei formed genuine blastulae in 13% of the cases, and most of the complete blastulae arrested before completing gastrulation. However, three embryos derived from adult germ cell nuclei did attain advanced stages of organogenesis and one of these developed into an abnormal feeding larva. These individuals are the most advanced nuclear-transplants obtained so far from nuclei of normal adult cells in vivo. Chromosome analyses performed on a sample of nuclear-transplants derived from germ cells revealed gross chromosomal abnormalities in all individuals except the larva. It is concluded, that even though germ cell nuclei are genetically totipotent, they, like somatic nuclei, undergo developmental restrictions during their process of cell differentiation, and after transplantation to host eggs, give rise to abnormal nuclear-transplants accompanied in most cases by karyotypic alterations. The significance of the developmental restrictions observed in germ cell nuclei is interpreted as an expression of chromosomal differentiation.