Estudo de associação genômica ampla (GWAS) para características de escore visual de conformação, precocidade e musculosidade na raça nelore

Abstract

Despite the great expressiveness of Brazil in relation to beef cattle, the Brazilian cattle herd is mostly composed of Zebu genes, which when compared to taurine breeds have lower performance and carcass quality. Characteristics evaluated by body scores such as: conformation (CONF), precocity (PREC) and musculature (MUSC) are important parameters for identifying animals with superior productive morphology. Genomic Wide Association Studies (GWAS) aim to understand the genetic structure through the expression of genes that influence certain productive traits. The objective of the work was to implement GWAS for the characteristics measured by visual scores CONF, PREC and MUSC for Nellore cattle, identifying genomic regions with greater effects, candidate genes, in addition to detecting physiological processes involved in the phenotypic variability of such characteristics. The phenotype information was collected from 20,807 animals, whose pedigree file totaled 39,508 individuals. The DNA information was extracted from genotyped cattle using the GGP-indicus 35K panel. The analyzes were performed by the single-step GWAS method (ssGWAS) using the BLUPF90 family programs, which measured the variations for genomic windows containing 10 continuous single nucleotide polymorphisms (SNPs). Candidate genes were identified by the ENSEMBL database, considering those whose regions presented values equal to or greater than 1% of the total additive genetic variance. The subsequent analyzes were those of genetic ontology (GO, PANTHER) and of gene connection networks (REVIGO), with the purpose of detecting which biological pathways the genes acted on, and the associated effect on the mentioned characteristics. For CONF, 27 genomic regions present in 7 different chromosomes were identified, harboring 27 candidate genes. A total of 26 genomic regions spread across 4 chromosomes, exposing 26 candidate genes were found for PREC. Regarding MUSC, 19 chromosomal regions associated with 26 genes located on 5 different chromosomes were observed. The results of ontological pathway analyzes revealed influential genes for CONF, including ALDH9A1, RXRG, RAB2A and CYP7A1, which are involved in lipid metabolism. The main genes identified for PREC were ELOVL5, PID1, DNER, TRIP12 and PLCB1, involved in the synthesis of long-chain fatty acids, regulation of cholesterol levels, lipid metabolism and muscle differentiation. For MUSC, the most prominent genes in biological pathways that result in the expression of muscle development were SEMA6A, TIAM2, UNC5A and UIMC1. The candidate genes reported in this study can be used in the future in breeding programs aiming to increase the genetic gain of growth traits in beef cattle.