High temporal-resolution transcriptome landscape reveals the biological process and regulatory genes of melanin deposition in breast muscle of Silkie chickens during embryonic development.

Background: Abnormal deposition of melanin in skeletal muscle is an interesting phenomenon and the Silkie is the most typical example. Melanin deposition involves multiple steps such as neural crest cell migration, melanocyte differentiation, melanosome assembly and melanin biosynthesis, which have already occurred during the embryonic stage of Silkies. However, there is no comprehensive understanding of the dynamic changes in the biological processes and regulatory mechanism underlying melanin deposition in skeletal muscle during chicken embryonic development.

Results: In this study, high-performance liquid chromatography (HPLC) was used to accurately measure the melanin content in breast muscle across 13 embryonic time points. There was no melanin in breast muscle on embryonic day 8 (E08) to E10, a trace amount of melanin on E11 to E16 and a large amount of melanin on E17 to E21. According to melanin content and deposition pattern, the melanin deposition process in breast muscle was further divided into five stages, including E08 to E10, E11 to E14, E15 to E16, E17 to E18, and E19 to E21. High temporal-resolution transcriptome analysis was performed in the breast muscle of Silkies across 13 embryonic time points. The protein-coding genes (PCGs) and transcriptional factors (TFs) significantly specifically expressed at these five stages were identified. Among these stage-specific genes, stage-specific DEGs between Silkies and Wenchang chickens without melanosis were further screened at each stage. During E08 to E10, three stage-specific DEGs and one stage-specific TF act on neural crest cell migration and melanocyte stem cell differentiation. During E17 to E21, nine stage-specific DEGs and one stage-specific TF act on melanosome assembly and melanin biosynthesis. During E19 to E21, one stage-specific DEG enhances melanin biosynthesis. These stage-specific DEGs and TFs all affect the final melanin content of breast muscle.

Conclusions: This study reveals the critical stage of melanin deposition in breast muscle during the embryonic development, and identified the biological processes and functional genes at each stage. This study provides novel insights into the biological process and regulatory mechanism of melanin deposition in skeletal muscle and provides a reference for breeding Silkies with high muscle melanin content.