Submitted to: The International Embryo Technology Society
Publication Type: Proceedings
Publication Acceptance Date: 11/2/2007
Publication Date: 1/8/2008
Citation: Hart, E.J., Pinton, A., Powell, A.M., Wall, R.J., King, W.A. 2008. Meiotic Recombination in Somatic Cell Nuclear Transfer Bulls and Their Offspring. Cytogenet.Genome Research 120(1-2), 97-101.
Technical Abstract: In mammals, homologous chromosome pairing and recombination are essential events for meiosis. The generation of reciprocal exchanges of genetic material ensure both genetic diversity and the proper segregation of homologous chromosomes. With the advent of reproductive biotechnologies such as somatic cell nuclear transfer (SCNT) in the livestock industry, these vital steps have begun to be bypassed. Despite this, there have been few studies carried out on the reproductive characteristics of cloned animals and none to date regarding the consequences on the meiotic process. As these procedures grow in popularity and use, it is increasingly evident the importance to evaluate the long-term viability, health and productivity of cloned animals and any subsequent offspring in future generations to validate potential applications of the technology. Previously, studies in recombination and synapsis have focused on the physical observation of chiasmata formation in meiotic chromosomes; however in recent years, the characterization of proteins that localize to the sites of crossing-over and of proteins present in the synaptonemal complex have allowed for the study of meiotic recombination using a precise direct immunocytogenetic approach. Cytological analysis of meiotic cells obtained from the testicular tissue of five normal bulls of proven fertility, two SCNT bulls containing two different transgenes (Powell et al., BOR 71:210-216, 2004) and four reproductively mature offspring of SCNT bulls was performed in order to detect the effects of SCNT on the meiotic process. Over 50 pachytene cells per animal were analysed by immunofluorescence using antibodies against the synaptonemal complex protein 3 (SCP3), and mismatch repair protein1 (MLH1) located on the cross over sites. The average number of crossing over per spermatocyte for the non-SCNT bulls (42 ± 4 SD, min:33 max:56,) , SCNT bulls (44 ± 4 SD, min:36 max: 59) and SCNT offspring (44 ± 4 SD min:37 max: 58) were quite similar between the cells of the same individual, however, inter-individual variation was observed. These results are the first documentation of the normal range of variability of recombination distribution within the cattle genome and suggest that the SCNT process does not affect meiotic recombination. (funded by NSERC and the CRC program)