Comparison of significant CSS regions between European and African Bos taurus
No candidate gene regions were found in common across the European and African cattle types. This may be due to the long-term differences in natural and production-oriented selective pressures in these diverse genetic archetypes (Edea et al. 2014; Gautier et al. 2009; Gautier and Naves 2011; Gibbs et al. 2009; Randhawa et al. 2014). Recent attempts to find the transferability of height-associated loci across human populations have shown comparable results (low consistency) for finding the same genetic variants when discoveries made in non-African ethnicities were compared in populations of African ancestry (Kang et al. 2010; Shriner et al. 2009). Our results indicate that there may be a persistent trend of dissimilarities for African genealogies across species, and some environmental factors would have shaped a comparatively different genetic architecture. We suggest that investigation of several other African breeds with sufficient sample sizes can further elaborate the nature of different candidate gene regions.
A region on BTA-13 harboring UQCC and GDF5 genes, which we putatively linked to bovine stature (Randhawa et al. 2014), was also not detected in this study. The absence of BTA-13 genes (UQCC and GDF5) as the possible candidate for bovine stature in this study are due to the sensitivity of CSS (and its constituent tests of selection) to the sample composition because the cohort composition between the two papers is quite different regarding inclusion and exclusion of several breeds. Moreover, another gene, ASIP (related to coat color), was also located at the BTA-13 peak, and ASIP may also be another plausible candidate of the signatures of selection detected in the previous study.
In comparison to previous findings in cattle, we note that some of the known genes and regions related to bovine stature were not detected here, mainly because they were identified in Bos indicus and composite breeds (Pryce et al. 2011). Moreover, genetic architecture of stature is not considered fully analogous in cattle and human; our results suggest that many common genes might be participating in the physiological control of stature in the two species (Pryce et al. 2011).
Characterization of biological function of candidate genes could help our understanding of mechanisms underlying stature diversity. Future research should focus on regional genomic sequencing (involving multiple genes) rather than single gene-centric approaches. In addition, gene networks and functional pathway analyses on subsets of genes identified by genome-wide association or selection scans can help uncover the biological processes in complex traits.