Inosine monophosphate (IMP) is a key factor affecting the fleshy flavor of meat; meanwhile, the free-range mode is an efficient strategy to improve muscular IMP content. To assess expression differences in IMP metabolism-related genes under different feeding patterns, Illumina Nextseq 500 sequencing was used to catalog the global gene expression profiles of muscle samples from Lueyang black-bone chicken under free-range and caging conditions. A total of 15510 unigenes were assembled, with 13423 (86.54%) and 6088 (39.25%) unigenes correctly annotated in the GO and KOG databases, respectively. Next, the "purine metabolism" pathway in the "nucleotide metabolism group" was assessed in depth. Through Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis, we retrieved 172 nucleotide- and 5 purine- metabolism related genes that were differentially expressed in muscle samples from free-range and caged chickens. At 60-day-old, AMPD1, NT5C1A and ENTPD8 showed higher levels in the free-range group, while only ENTPD8 was upregulated in 120-day-old chickens. In addition, GART, GARS and ADSL in free-range chickens showed higher levels compared with caged animals. Furthermore, IMPDH levels in free-range chicken were lower than those of caged chicken. Real-time quantitative polymerase chain reaction (qPCR) was used to validate the above findings. These results revealed a set of differentially expressed genes potentially related to IMP metabolism in chicken under different breeding modes, providing novel insights into controlling IMP levels in chicken meat.

The CRISPR/Cas9 system has enabled highly efficient genome targeted editing for various organisms. However, few studies have focused on CRISPR/Cas9 nuclease-mediated chicken genome editing compared with mammalian genomes. The current study combined CRISPR with yeast Rad52 (yRad52) to enhance targeted genomic DNA editing in chicken DF-1 cells. The efficiency of CRISPR/Cas9 nuclease-induced targeted mutations in the chicken genome was increased to 41.9% via the enrichment of the dual-reporter surrogate system. In addition, the combined effect of CRISPR nuclease and yRad52 dramatically increased the efficiency of the targeted substitution in the myostatin gene using 50-mer oligodeoxynucleotides (ssODN) as the donor DNA, resulting in a 36.7% editing efficiency after puromycin selection. Furthermore, based on the effect of yRad52, the frequency of exogenous gene integration in the chicken genome was more than 3-fold higher than that without yRad52. Collectively, these results suggest that ssODN is an ideal donor DNA for targeted substitution and that CRISPR/Cas9 combined with yRad52 significantly enhances chicken genome editing. These findings could be extensively applied in other organisms.