Transcriptome Sequencing and Identification of APOE Gene Polymorphisms, Their Expression and Their Relationship with Body Size Traits in Guizhou White Goats (Capra hircus)

Carcass growth and development are crucial evaluation indicators influencing the economic efficiency of goats (Capra hircus). This study aimed to screen the nucleotide variation sites (SNPs) of the APOE gene in Guizhou white goats and explore the correlation between APOE gene variations and body size traits, as APOE had been identified as a key candidate gene regulating growth and development in this breed through transcriptome sequencing screening. A total of 324 Guizhou white goats were used in this study for SNP detection, population genetic analysis, real-time fluorescence quantitative PCR (RT-qPCR) and association analysis. The results showed that one nucleotide mutation site (g.353 A > G) was detected in the APOE gene, which yielded two alleles (A and G) and three genotypes (AA, AG and GG). The site exhibited moderate polymorphism and conformed to Hardy–Weinberg equilibrium. The mRNA expression level of APOE in longissimus dorsi muscle was significantly higher in males than in females. Association analysis revealed a sex-specific effect of this locus on body size traits. The A allele and AA genotype were significantly associated with increased body weight and heart girth in females, whereas no significant effect was detected in males. Therefore, the identified APOE gene mutation site can serve as a candidate molecular marker for the early selection of growth traits in Guizhou white goats.