Fertility of hybrids of dromedary and Bactrian camels: A possible role of conserved architecture of zinc finger domain of recombination regulator PRDM9

Recombination regulator, PRDM9, has been regarded as the most rapidly evolving gene in the genomes of many metazoans, in addition to being acknowledged as the sole speciation gene in vertebrates. It has become the focus of many scientific investigations because of exceptional numerical and sequence variability in its zinc finger (ZF) domain within and across species that contributes to reproductive isolation between species. This study is the maiden attempt to explore the architecture of PRDM9 ZF domain in two Camelid species (Camelus dromedarius and Camelus bactrianus). Sequence analysis revealed highly conserved domain architecture with presence of 3 and 4 ZFs in dromedary and Bactrian camels, respectively. Typical evolutionary features of PRDM9 ZF domain i.e. concerted evolution and positive selection were invariably absent in both the one-humped dromedary and the two-humped Bactrian camels. Fertility of hybrids of dromedary and Bactrian camels, despite being taxonomically distinct species can be attributed to the lack of sequence variability in PRDM9 in these species. Phylogenetic analysis underpinned clear demarcation of camels from other livestock species. The results of the present study defy what has been learnt so far about PRDM9 and add to the enigma surrounding the most intriguing gene in the genome.

Automated summary

The PRDM9 gene is considered as the most rapidly evolving gene in many organisms' genomes and the sole speciation gene in vertebrates. This study explored the architecture of the PRDM9 zinc finger (ZF) domain in dromedary and Bactrian camels. The results showed that the ZF domain in both camels exhibited a highly conserved architecture, and lacked the typical evolutionary features of PRDM9. The low sequence variability of PRDM9 in these camel species may explain the fertility of hybrids between them. Additionally, phylogenetic analysis clearly distinguished camels from other livestock species. These findings challenge our understanding of PRDM9 and add to the mystery surrounding this gene.