Refining the Camelus dromedarius Myostatin Gene Polymorphism through Worldwide Whole-Genome Sequencing

Simple Summary The dromedary is a multipurpose livestock species. Growing interest in dromedary meat production, increasing intensification of meat production systems and rising business turnover for the dromedary athletic competition sector point to the need for a more effective genetic selection. To this aim, the identification of genetic markers, to be implemented in phenotype-genotype association studies, represents a pre-requisite. The myostatin gene is known to affect, to a various extent, muscularity in several animal species. In this study, we investigated the dromedary myostatin gene sequence variation through the analysis of data from 183 worldwide animals. A total of 99 variants were detected in the target region. Through a bioinformatic approach, we explored the possible functional effects of the detected variants. Several hints emerged, suggesting that natural variants at the dromedary myostatin locus may determine quali-quantitative changes in the myostatin expression, thus likely impacting on dromedary muscularity. Further efforts are needed to collect reliable phenotypic data on dromedary muscularity and racing performances, thus allowing for the unveiling of those genetic markers that are associated with the phenotypic variability in muscularity-related traits. Under intensive rearing systems, large-scale screening of genotypes at those markers in dromedary populations will effectively orient selection decisions and positively impact on rates of genetic gain. Myostatin (MSTN) is a highly conserved negative regulator of skeletal muscle in mammals. Inactivating mutations results in a hyper-muscularity phenotype known as "double muscling" in several livestock and model species. In Camelus dromedarius, the gene structure organization and the sequence polymorphisms have been previously investigated, using Sanger and Next-Generation Sequencing technologies on a limited number of animals. Here, we carried out a follow-up study with the aim to further expand our knowledge about the sequence polymorphisms at the myostatin locus, through the whole-genome sequencing data of 183 samples representative of the geographical distribution range for this species. We focused our polymorphism analysis on the +/- 5 kb upstream and downstream region of the MSTN gene. A total of 99 variants (77 Single Nucleotide Polymorphisms and 22 indels) were observed. These were mainly located in intergenic and intronic regions, with only six synonymous Single Nucleotide Polymorphisms in exons. A sequence comparative analysis among the three species within the Camelus genus confirmed the expected higher genetic distance of C. dromedarius from the wild and domestic two-humped camels compared to the genetic distance between C. bactrianus and C. ferus. In silico functional prediction highlighted: (i) 213 differential putative transcription factor-binding sites, out of which 41 relative to transcription factors, with known literature evidence supporting their involvement in muscle metabolism and/or muscle development; and (ii) a number of variants potentially disrupting the canonical MSTN splicing elements, out of which two are discussed here for their potential ability to generate a prematurely truncated (inactive) form of the protein. The distribution of the considered variants in the studied cohort is discussed in light of the peculiar evolutionary history of this species and the hypothesis that extremely high muscularity, associated with a homozygous condition for mutated (inactivating) alleles at the myostatin locus, may represent, in arid desert conditions, a clear metabolic disadvantage, emphasizing the thermoregulatory and water availability challenges typical of these habitats.