Metabolome and transcriptome analyses reveal the mechanism underlying the differences in skin development between the two duck breeds during embryonic stage.

Skin color of poultry, an important economic trait, is related to breed, feed, environment, and other factors. In recent years, China's duck industry has developed rapidly, and duck products are welcomed by consumers. Different skin colors of ducks have different cooking methods. Black skinned duck, such as Yulin black duck, is more popular in China because they are considered more suitable for making soup, while other skin colors, such as Pekin duck, is used for roasting. In order to gain a deeper understanding of the genetic factors associated with differences in duck skin color, the transcriptomes and metabolomes of skin between Yulin black duck and Pekin duck from 15 (BSE15 vs. PSE15), 21 (BSE21 vs. PSE21) and 27 (BSE27 vs. PSE27) days of incubation were compared and analyzed. The transcriptome results showed that a total of 187 (118 up-regulated and 69 down-regulated), 417 (91 up-regulated and 326 down-regulated) and 137 (55 up-regulated and 82 down-regulated) differentially expressed genes (DEGs) were identified from BSE15 vs. PSE15, BSE21 vs. PSE21 and BSE27 vs. PSE27, respectively. The significantly enriched GO terms of biological process were positive regulation of melanin biosynthetic process, melanin biosynthetic process, cuticle development, melanin biosynthetic process from tyrosine, and melanocyte differentiation, which were potentially related to skin growth and development. Eleven significant pathways, highly enriched by DCT, TYR, ASIP, TYRP1, KIT, PHOSPHO2, CERS3, SGPP2, SPTLC3, DEGS2, PATJ, RBP7, AOX1, ETNPPL, HPGDS, and GAD1, were melanogenesis, tyrosine metabolism, vitamin B6 metabolism, sphingolipid metabolism, protein digestion and absorption, tight junction, alpha-linolenic acid metabolism, arachidonic acid metabolism, linoleic acid metabolism, nicotinate and nicotinamide metabolism, and alanine, aspartate and glutamate metabolism, which participated in regulating the development of duck skin during embryonic stage. The significantly different metabolites (SDMs) were mainly organoheterocyclic compounds, lipids and lipid-like molecules, organic oxygen compounds, organic acids and derivatives, including L-tyrosine, N-arachidonyl maleimide, glycerophospho-N-palmitoyl ethanolamine, LPE 22:4, and PC(0:0/18:0). which were mainly enriched in glycerophospholipid metabolism, arachidonic acid metabolism, linoleic acid metabolism, alpha-linoleic acid metabolism, and melanogenesis in metabolome, suggesting that these pathways may play important roles in skin development of duck during embryonic stage. Besides, the analysis of integrated transcriptome and metabolome indicated that the pathways, including glycerophospholipid metabolism, arachidonic acid metabolism, linoleic acid metabolism, and alpha-linolenic acid metabolism, could contribute to regulating skin development in embryonic duck. Our findings could help elucidate the genetic mechanisms underlying the development differences in duck skin color. Furthermore, the candidate genes and metabolites can be used to provide a valuable breeding strategy for the selection of specific duck breeds with ideal skin coloration.