Abstract
The Xichuan black-bone chicken, which is a rare local chicken species in China, is an important genetic resource of black-bone chickens. Tyrosine can affect melanin production, but the molecular mechanism underlying tyrosine-induced melanin deposition in Xichuan black-bone chickens is poorly understood. Here, the blackness degree and melanin content of the breast muscle of Xichuan black-bone chickens fed a basic diet with five levels of added tyrosine (i.e., 0.2, 0.4, 0.6, 0.8, and 1.0%; these groups were denoted test groups I-V, respectively) were assessed, and the results showed that 0.8% tyrosine was the optimal level of added tyrosine. Moreover, the effects of tyrosine supplementation on the proliferation and tyrosinase content of melanocytes in Xichuan black-bone chickens were evaluated. The results revealed a dose-dependent relationship between tyrosine supplementation and melanocyte proliferation. In addition, 417 differentially expressed genes (DEGs), including 160 upregulated genes and 257 downregulated genes, were identified in a comparative analysis of the transcriptome profiles constructed using the pooled total RNA from breast muscle tissues of the control group and test group IV, respectively (fold change ≥2.0, P < 0.05). These DEGs were mainly involved in melanogenesis, the calcium signaling pathway, the Wnt signaling pathway, the mTOR signaling pathway, and vascular smooth muscle contraction. The pathway analysis of the DEGs identified some key genes associated with pigmentation, such as DCT and EDNRB2. In summary, the melanin content of breast muscle could be markedly enhanced by adding an appropriate amount of tyrosine to the diet of Xichuan black-bone chickens, and the EDNRB2-mediated molecular regulatory network could play a key role in the biological process of tyrosine-induced melanin deposition. These results have deepened the understanding of the molecular regulatory mechanism of melanin deposition in black-bone chickens and provide a basis for the regulation of nutrition and genetic breeding associated with melanin deposition in Xichuan black-bone chickens.
Highlights
The black-bone chicken is an important resource in poultry production, and the fact that its body contains melanin significantly differentiates it from other chicken breeds (Tian et al, 2007; Tu et al, 2009b; Yu et al, 2018a)
The results indicate that dietary supplementation with different doses of tyrosine significantly improved the breast muscle blackness (Figure 1A) and increased the melanin content in the breast muscle of Xichuan black-bone chickens (Figure 1B)
The lowest melanin content in breast muscle was detected in the control group, and a slightly increased content was found in test group I, but no significant differences were found between test group I and the control group (P > 0.05)
Summary
The black-bone chicken is an important resource in poultry production, and the fact that its body contains melanin significantly differentiates it from other chicken breeds (Tian et al, 2007; Tu et al, 2009b; Yu et al, 2018a). Many studies have shown that black-bone chickens have medical benefits, such as antioxidant activity (Xin et al, 2009) and the abilities to delay aging (Xu et al, 1999), treat anemia (Xie et al, 2009) and cure female menstrual abnormalities (Tu et al, 2009a) Due to their unique edible and medicinal value, black-bone chickens are highly preferable by consumers, and the exploitation and genetic breeding of black-bone chicken resources have become increasingly important. The elucidation of the above mechanism is of great significance for improving the meat quality of black-bone chickens through the regulation of nutrition and for identifying the molecular markers related to melanin deposition in the breeding of black-bone chickens. The molecular mechanism underlying tyrosine-induced melanin deposition in black-bone chickens remains poorly understood
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