| Male frogs, Rana pipiens, were injected intraperitoneally with a mutagen, triethylenemelamine (TEM) 650 (mu)g/kg of frog. Seven days after administration, spermiation was induced with human chorionic gonadotropin and the ova of normal females were inseminated with the sperm. The embryos were allowed to develop to the blastula stage, following which they were used as donor cells in nuclear transplantation (NT) studies.;Nuclei from a TEM-treated blastula, were transplanted into activated and enucleated ova of untreated females to produced a number of embryos. Results indicated that clones of embryos produced from TEM-blastulae were anatomically abnormal and that the abnormalities were not uniform within a clone. Moreover, chromosomal abnormalities were prevalent among TEM-NT embryos.;This suggests that cells of a TEM-blastula vary and TEM-damage occurs at different parts of the chromosome. The events that lead to the formation of the diverse embryonic abnormalities is unknown. One possibility is that defective chromosomes from the TEM-treated male may have undergone an independent assortment during cell division post-fertilization, thus producing combinations of abnormal chromosomes resulting in assorted abnormal embryos. The second possible explanation concerns the alternation by TEM to male gametes pre-fertilization. The sperm thus carries the defective chromosomes which may result in ensuing translocation. The third alternative possibility involves DNA-repair mechanisms which may vary in different genomes and different cells, resulting in phenotypic abnormalities among embryos.;A clone that has genetic differences is unexpected and provides unique insight into the nature of mutagenic insult. To assure that the abnormal morphology seen was not due to technical error, serial nuclear transplantation was performed. The nuclear transplanted blastula served as a nuclear donor on day 2, and the procedure was repeated.;Results indicated that individuals in a clone of serial nuclear transplantation from a given TEM-blastula revealed more structural homogeneity than those from different TEM-blastula.;The principle finding of this study is that a blastula resulting from a sperm of a mutagen-treated male is composed of a diversity of different kinds of cells, and has profound importance for the interpretation of the dominant lethal test. With the nuclear transplantation technique, the amplification of a mutagenic event can be studied. |
