Submitted to: Cytogenetics and Genome Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/2/2007
Publication Date: 1/1/2008
Citation: Hart, E.J., Pinton, A., Powell, A., Wall, R., and King, W.A. 2008. Meiotic recombination in normal and clone bulls and their offspring. Cytogenetic and Genome Research. 120(1-2): 97-101. Interpretive Summary: Gametes are formed during the process of meiosis, an essential step in sexual reproduction. During this process of egg and sperm formation, the DNA strands break and rejoin (crossover) with one another. This crossover event is the mechanism by which genetic diversity is established. Somatic cell nuclear transfer (cloning) bypasses this important step in development. The experiment reported here was designed to determine if the crossover recombination event is normal in clones and their offspring during spermatogenesis. We harvested testis from 11 sexually mature bulls (5 controls, 2 clones and 4 offspring of clones) and examined them to determine if the crossover rate differed among the groups. Nearly 600 meiotic events were observed. The number of recombination foci (point at which a crossover was taking place) averaged 42 ± 4, 43 ± 5 and 44 ± 5 for controls, clones and offspring of clones respectively. These values are with in the normal range for bulls. Therefore, this data suggests that somatic cell nuclear transfer does not alter the ability of clones or their offspring to participate in recombination events during the formation of spermatogonia.
Technical Abstract: Homologous chromosome pairing and recombination are essential components of meiosis and sexual reproduction. The reshuffling of genetic material through breakage and reunion of chromatids ensure proper segregation of homologous chromosomes in reduction division and genetic diversity in the progeny. The advent of somatic cell nuclear transfer (SCNT) as a reproductive biotechnology for use in livestock industry has made it easy to bypass these vital steps. It is not known if the meiotic processes in these animals is normal. In an attempt to assess the impact of cloning by SCNT on the meiotic processes, we undertook an immunocytological comparison of recombination in normal and cloned bulls using antibodies raised against the synaptonemal complex Protein 3 (SCP3) to label the lateral elements, and the mismatch repair protein 1 (MLH1) foci on bivalents as indicators of recombination events. Our studies involving five normal bulls of proven fertility, two SCNT-derived bulls and four mature offspring of SCNT bulls showed that the mean number of crossing over per spermatocyte for normal bulls (42 ± 4 SD), ranging from 33 to 56), was not significantly different from that of SCNT-derived bulls (43 ± 5SD (ranging from 35 to:56), and the offspring of SCNT-derived bulls (46 ± 4SD) ranging from 37 to 58). It would appear that circumventing meiosis to produce these animals does not influence the meiotic processes revealed by MLH1 foci detected in spermatocytes.