# Visceral Peritoneum Hyperpigmentation in Chickens Is Associated with DCT Expression

## TL;DR

Dark pigmentation in chicken abdomens is caused by overactivity of the DCT gene, and this discovery can help improve meat quality through selective breeding.

## Contribution

The study identifies DCT gene overexpression as the cause of visceral peritoneum hyperpigmentation in chickens and proposes it as a genetic marker for breeding.

## Key findings

- DCT overexpression increases melanin production and melanocyte proliferation in chickens.
- A DCT polymorphism (g.147917398 C > T) is a potential marker for genetic selection to reduce hyperpigmentation.
- Excessive eumelanin deposition in the peritoneum is confirmed as the cause of the pigmentation abnormality.

## Abstract

Some chickens develop dark pigmentation inside their abdomen, known as hyperpigmentation of the visceral peritoneum. This condition lowers the visual quality of the meat, reduces its market appeal, and leads to economic losses for the poultry industry. It is especially common in certain native Chinese chicken breeds. While it is known that pigment-producing cells are involved, the exact cause of this abnormal coloring is unclear. In this study, we used advanced genetic and cellular tools to understand the condition. We discovered that the dark patches are caused by a natural pigment called melanin, and a gene named DCT plays a key role in producing this pigment. When this gene becomes overactive, it causes pigment cells to grow and produce more melanin than usual. We also identified a specific genetic change in DCT that can help the poultry industry identify birds more likely to develop this condition. Our findings provide a practical solution to reduce the occurrence of this trait through selective breeding. This can improve carcass quality, reduce waste, and increase profitability. Overall, the study helps us better understand how pigmentation works in animals and offers a clear path to improving meat quality in poultry production.

Hyperpigmentation of the visceral peritoneum (HVP) is a pigmentation abnormality in chickens that adversely affects carcass appearance, consumer acceptance, and poultry production. However, the genetic basis of HVP remains unclear. To investigate the causes and regulatory mechanisms of HVP, we employed high-performance liquid chromatography (HPLC), bulk RNA sequencing (RNA-seq), qRT-PCR, Western blotting, and siRNA interference. Additionally, single-cell RNA sequencing (scRNA-seq) was used to examine gene expression at the cellular level. Anatomical examination and hematoxylin and eosin (HE) staining revealed melanin deposition in the peritoneum of HVP-affected chickens. Spectrophotometric analysis at 500 nm showed significantly higher absorbance in the HVP group (p < 0.05), which correlated with the degree of pigmentation. HPLC confirmed the pigmentation as eumelanin, based on the pyrrole-2,3,5-tricarboxylic acid (PTCA) peak. RNA-seq identified 61 differentially expressed genes. Functional studies showed that dopachrome tautomerase (DCT) overexpression, combined with L-tyrosine (L-Tyr) supplementation, significantly increased melanin content (p < 0.05) and promoted melanocyte proliferation. In contrast, DCT silencing reduced melanin secretion and inhibited cell growth. ScRNA-seq analysis of over 9700 high-quality cells identified distinct melanocyte clusters, with DCT expression approximately 2.5-fold higher in melanocytes from the HVP group compared to the normal group. Furthermore, a DCT polymorphism (g.147917398 C > T) was identified as a potential marker for genetic selection (p-values = 0.033). These findings demonstrate that HVP is driven by DCT overexpression and excessive eumelanin deposition. DCT could serve as a molecular marker for genomic selection to improve poultry carcass quality and reduce economic losses in the poultry industry.