Transcriptome Analysis of Adipose Tissues from Five Sheep Breeds Reveals Key Genes Involved in Fat Deposition

Background: Sheep (Ovis aries) exhibit significant diversity in adipose tissue deposition, which influences meat quality, environmental adaptation, and economic value. Tail fat, in particular, varies widely among breeds, yet the transcriptomic basis of this variation remains incompletely understood. This study aims to systematically compare the transcriptional profiles of five adipose depots across five sheep breeds to identify molecular mechanisms underlying fat deposition and tail phenotype divergence. Methods: We analyzed 250 publicly available RNA-seq samples from five adipose tissues (caul, subcutaneous, perirenal, intermuscular, and tail fat) of five sheep breeds (Altay, Tibetan, Merino, Wadi, Small-tailed Han). Data were processed using FastQC, STAR, and featureCounts. Differential expression analysis was performed with DESeq2, followed by GO and KEGG enrichment analyses. Breeds were grouped into three tail phenotypes: fat-tailed, short fat-tailed, and thin-tailed. Cross-tissue and phenotype-specific pathway analyses were conducted to identify key regulatory genes. Results: Transcriptional divergence was most pronounced in subcutaneous and intermuscular fat, while tail fat exhibited both conserved and phenotype-specific pathways. Fat-tailed breeds showed enrichment in mitochondrial oxidative phosphorylation and lipid biosynthesis genes (TAFAZZIN, GPAM, COQ family). Short fat-tailed breeds were characterized by extracellular matrix remodeling genes (MMP9, MMP12, MMP19). Thin-tailed sheep lacked these pro-lipogenic and structural remodeling pathways. A dual-axis model of tail fat development is proposed to explain phenotypic diversity. Conclusions: This study reveals that distinct molecular mechanisms underpin tail fat phenotypes in sheep: fat-tailed breeds prioritize metabolic efficiency, short fat-tailed breeds rely on ECM remodeling, and thin-tailed breeds lack these enhancements. The identified candidate genes may serve as potential targets for molecular breeding strategies aimed at optimizing fat deposition and adaptive traits in sheep.