Regiões de variações no número de cópias (cnvr) associadas a medidas morfométricas e pontuações de morfologia e marcha em equinos da raça campolina

Abstract

Morphometric measurements are a set of morphological traits relevant to the selection and genetic improvement of horses, as they directly influence conformation and functional performance. Investigating the genetic factors underlying these traits is essential to enhance selection strategies. In this context, copy number variations (CNVs) represent an important source of genomic diversity and may impact genes involved in skeletal growth and development. This study aimed to perform a genome-wide association study (GWAS) using copy number variation regions (CNVR) in Campolina horses, focusing on the identification of genomic regions associated with morphometric traits. Phenotypic data of 15 morphometric measurements were analyzed from 240 Campolina horses provided by ABCCCampolina. DNA was extracted from hair bulb samples, and genotyping was performed using the Equine Plus Illumina-70K chip (NEOGEN). Quality control excluded phenotypic outliers and genotypes with a call rate lower than 95%, resulting in 239 animals and 56,364 SNPs. CNV detection was conducted using the PennCNV software, and CNVRs were identified with CNVRuler, considering regions with at least three SNPs, minor allele frequency (MAF) greater than 0.02, CNVR separated into gains and losses, and a recurrence rate threshold of 0.1. The statistical model applied was linear regression, including sex, age at registration, and state of birth as fixed effects. Gene annotation, QTL enrichment were performed using the GALLO package in R, and functional enrichment of CNVRs (p < 0.05) was assessed using VarElect. A total of 384 CNVs were detected in Campolina horses, grouped into 212 CNVRs. For height-related traits, 12 CNVRs were significantly associated with withers height, including one exclusive region harboring the candidate gene SMARCAL1 (ECA6). For croup height, 11 CNVRs were identified, with one exclusive region containing the gene SLC39A13 (ECA12). For back height, 10 CNVRs were associated, with the candidate gene MAP2K2 (ECA7). For flank height, 24 CNVRs were significantly associated, including two exclusive regions harboring the genes SLC38A7 (ECA3) and PTPN1 (ECA22). Regarding length-related traits, for head length, 13 CNVRs were associated, one being exclusive with the gene LRRTM4 (ECA15). For neck length, 15 CNVRs showed association, including two exclusive CNVRs harboring DOCK1 (ECA1) and KIF2B (ECA11). For back-loin length, 14 CNVRs were associated, with one exclusive region containing ROR2 (ECA23). For croup length, nine CNVRs were identified, including two exclusive regions harboring PTGER3 (ECA5) and SLAIN1 (ECA17). For shoulder length, only two CNVRs were associated, harboring TSC22D1 (ECA17) and LRBA (ECA2). For body length, 13 CNVRs were associated, with four exclusive regions containing NAGEL2 (ECA1) and TCF4 (ECA8). Regarding width measurements, for head width, four CNVRs were associated, two of which were exclusive, harboring ERCC3 (ECA18) and RABGAP1 (ECA25). For chest width, 10 CNVRs were associated, including four exclusive regions containing TUBB (ECA20), TWIST1 (ECA4), and CDH9 (ECA21). For hip width, 14 CNVRs were identified, with one exclusive region harboring OSGEP (ECA1). Finally, regarding perimeter measurements, thoracic circumference showed 10 associated CNVRs, two of which were exclusive, harboring RPL26 (ECA23) and TAX1BP1 (ECA4). For cannon bone circumference, 20 CNVRs showed significant association, including two exclusive regions associated with ZNF280B, PRAME (ECA8), and CDH9 (ECA21). The findings 32 of this study indicate that CNVRs influence the morphometric traits of Campolina horses, suggesting the existence of genomic regions involved in skeletal growth and development. Furthermore, these results highlight the need for additional functional studies focusing on each candidate gene to clarify their roles in regulating these traits.