Prioritizing Fertility-Related Genes in Cattle Through Systems Genomics Data Integration

Abstract Female fertility significantly affects the efficiency of cow-calf production. Despite the collective efforts to understand the complex regulation of reproductive traits, causative genes and/or mutations have yet to be reported. Using omics technologies, such as gene expression, may unveil potential regulatory mechanisms and provide opportunities that link genotype to phenotype. Among them, expression quantitative trait loci (eQTL) are a powerful tool to identify biological mechanisms and potential markers for improving fertility. This study aimed to identify eQTLs underlying fertility-related traits and their co-localization with previously annotated QTLs. RNA-Seq from uterine epithelial cells (GSE171577) from crossbreed cows (n = 18 non-pregnant – NP and n = 25 pregnant – P) were used for gene expression analysis and SNP calling. Raw data quality control was performed, and read mapping was carried out using STAR. Genes were normalized to counts per million (CPM) and then the CPM values were log2 transformed using edgeR. Next, uniquely mapped reads were used for variant detection using the GATK software. Significant eQTLs were compared with the Animal Genome cattle database (QTLdb) to identify overlapping QTL regions. After quality control, 43 samples, 203,404 SNPs, and 15,029 genes were used for eQTL analysis. Using an additive linear model from the Matrix eQTL R-package, we identified 3,989 cis- and 7,683 trans-eQTLs for 1,120 and 2,503 genes, respectively (FDR < 0.05). A total of 50 cis-eQTLs were previously reported as differentially expressed genes, including CD37, CXCL3, PILRA, and PPP6R1 genes. The QTLs from QTLdb overlapping with our eQTLs were associated with traits such as age at puberty, conception rate, fertility index, and luteal activity (FDR < 0.05). Additionally, QTLs for production traits, such as milk production and body weight gain, were over-represented by the eQTLs we have identified. Significant biological processes underlying cis-regulated genes retrieved from ShinyGO were related to antigen processing and presentation. Likewise, trans-eQTLs genes were involved with transcription cis-regulatory region binding and transcription regulator activity. Our study provides novel regulatory and potential causative genetic variants, biological pathways, and genes underlying fertility in cows. Annotation and co-localization of detected eQTLs retrieved genomic regions previously reported as QTLs for production and reproduction-related traits. Further investigation, however, is required to untangle the mechanisms modulating gene expression and its effects on fertility-related traits.