Progressive erosion of the Relaxin1 gene in bovids

The relaxin/insulin-like (RLN/INSL) gene family is a group of genes that encode peptide hormones involved in a variety of physiological functions related to reproduction. Previous studies have shown that relaxin plays a key role in widening of the pubic bone during labor and in gamete maturation. Because of these functions, studying the evolution of RLN1, the gene encoding for relaxin, is relevant in livestock species, most of which belong in the group Laurasiatheria, which includes cow, pig, horse, goat, and sheep in addition to bats, cetaceans and carnivores. Experimental evidence suggests that cows do not synthesize relaxin, but respond to it, and sheep apparently have a truncated RLN1 gene. Thus, we made use of genome sequence data to characterize the genomic locus of the RLN1 gene in Laurasiatherian mammals to better understand how cows lost the ability to synthesize this peptide. We found that all ruminants in our study (cow, giraffe, goat, sheep and Tibetan antelope) lack a functional RLN1 gene, and document the progressive loss of RLN1 in the lineage leading to cows. Our analyses indicate that 1 - all ruminants have lost all key regulatory elements upstream of the first exon, 2 - giraffe, goat, sheep and Tibetan antelope have multiple inactivating mutations in the RLN1 pseudogene, and 3 - the cow genome has lost all traces of RLN1. The 5′ regulatory sequence plays a key role in activating expression, and the loss of this sequence would impair synthesis of mRNA. Our results suggest that changes in regulatory sequence preceded mutations in coding sequence and highlight the importance of these regions in maintaining proper gene function. In addition, we found that all bovids examined posses copies of the relaxin receptors, which explains why they are able to respond to relaxin despite their inability to produce it.