Background: The thin-tailed sheep breeds from Europe and the fat-tailed sheep breeds from China exhibit distinct phenotypic differences in fat deposition and meat production traits. However, the molecular mechanisms underlying gene expression related to these phenotypic differences are not well understood. Allele-specific expression (ASE) refers to the significant imbalance of expression levels of two parental alleles. Characterization of such events in F1 hybrid offspring generated from these two groups of sheep breeds can minimize the external factors influencing gene expression and reveal the variants with a cis -regulatory effect on gene expression. The aim of the present study was to investigate the genetic factors that influence different fat-deposition and meat production traits between thin- and fat-tailed sheep.
Results: Fifteen F1 hybrids were generated from crosses between Texel and Kazakh sheep as the representative phenotypes of thin- and fat-tailed breeds, respectively. Totally, 33 whole genomes from F1 individuals and their parents were sequenced with an average depth of ~17.21× coverage per sample. ASE analysis results from 70 RNA-seq samples of adipose and skeleton muscle tissues showed 128 ASE candidate genes were related to the function of fat deposition and meat production traits. A genome-wide scan of selective sweeps was also conducted between these two groups of sheep breeds in an effort to identify genomic regions related to fat deposition and meat production, respectively. We detected signatures of selection in ASE genes associated with fat deposition (e.g., PDGFD ) and meat production traits (e.g., LRCC2 ). Further analysis suggested that PDGFD and LRCC2 genes were speculated to be causative genes for fat deposition and meat production traits in sheep, respectively. Furthermore, AMPK signaling pathway was significantly enriched in ASE genes related to fatty acid biosynthesis in both adipose and skeleton muscle tissues, while PPAR signaling pathway was significantly enriched in ASE genes related to lipid metabolism in adipose tissue.
Conclusions: Our finding illustrates that the expression of identified ASE genes could potentially lead to the differences in traits of fat deposition and meat production between thin- and fat-tailed sheep. Keywords: allele-specific expression, phenotypic difference, thin- and fat-tailed sheep, whole-genome sequencing, transcriptome