Abstract
BackgroundCrossover localization during meiotic recombination is mediated by the fast-evolving zinc-finger (ZnF) domain of gene PRDM9. To study its impact on dairy cattle performance, we compared its genetic variation between the relatively small Israeli (IL) Holsteins and the North American (US) Holsteins that count millions.ResultsInitially, we analyzed the major BTA1 haplotypes present in IL Holsteins based on the 10 most telomeric SNPs of the BovineSNP50 BeadChip. Sequencing of representative haplotype carriers indicated that for all frequent haplotypes (> 6%), the variable PRDM9 ZnF array consisted of seven tandem ZnF repeats. Two rare haplotypes (frequency < 4%) carried an indicine PRDM9, whereas all others were variants of the taurine type. These two haplotypes included the minor SNP allele, which was perfectly linked with a previously described PRDM9 allele known to induce unique localization of recombination hotspots. One of them had a significant (p = 0.03) negative effect on IL sire fertility. This haplotype combined the rare minor alleles of the only SNPs with significant (p < 0.05) negative substitution effects on US sire fertility (SCR). Analysis of telomeric SNPs indicated general agreement of allele frequencies (R = 0.95) and of the substitution effects on sire fertility (SCR, R = 0.6) between the US and IL samples. Surprisingly, the alleles that had a negative impact on male fertility had the most positive substitution effects on female fertility traits (DPR, CCR and HCR).ConclusionsA negative genetic correlation between male and female fertility is encoded within the BTA1 telomere. Cloning the taurine PRDM9 gene, which is the common form carried by Holsteins, we encountered the infiltration of an indicine PRDM9 variant into this population. During meiosis, in heterozygous males, the indicine PRDM9 variant may induce incompatibility of recombination hotspots and male infertility. However, this variant is associated with favorable female fertility, which would explain its survival and the general negative correlation (R = − 0.3) observed between male and female fertility in US Holsteins. Further research is needed to explain the mechanism underlying this positive effect and to devise a methodology to unlink it from the negative effect on male fertility during breeding.
Highlights
Crossover localization during meiotic recombination is mediated by the fast-evolving zinc-finger (ZnF) domain of gene PR/SET Domain 9 (PRDM9)
The fastevolving ZnF array encoded by this exon was the source of all variation between the dairy and beef forms of PRDM9, resulting in a longer 727-amino-acid dairy variant compared to the reference protein of 725 amino acids from beef cattle (Fig. 1)
We show that this scheme is further complicated by the negative genetic correlation between male and female fertility that is encoded in the Bos taurus autosome 1 (BTA1) telomere
Summary
Crossover localization during meiotic recombination is mediated by the fast-evolving zinc-finger (ZnF) domain of gene PRDM9. PRDM9 is annotated at the telomeric end of Bos taurus autosome 1 (BTA1) (GenBank: NP_001306826) including four major functional domains, two of which, Krüppel Associated Box (KRAB) and SSX Repression Domain (SSXRD) nuclear localization signal, are associated with transcription repression This transcription-repression-like module is followed by a SET domain that provides methyltransferase activity and a C2H2 zinc finger (ZnF) array that binds to DNA. The ZnF array directs the specific binding of PRDM9 to sites across the chromosomes, and the SET domain produces H3K4me and H3K36me trimethylations to nearby histones [10] These modifications serve to recruit the SPO11 initiator of meiotic double stranded breaks topoisomerase (SPO11) to initiate double-strand breaks by a mechanism that involves protein–protein interactions with PRDM9’s transcription-repression-like module and that eventually promotes crossing over [10]
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