# Epigenetic landscape reveals MEF2 and SIX family-mediated transcriptional networks underlying dietary NFC/NDF ratio-induced muscle development and meat quality in Tibetan sheep

## TL;DR

This study shows how adjusting the diet of Tibetan sheep affects muscle development and meat quality through epigenetic changes linked to MEF2 and SIX transcription factors.

## Contribution

The study identifies MEF2 and SIX family transcription factors as key regulators of muscle development in Tibetan sheep under different dietary NFC/NDF ratios.

## Key findings

- A dietary NFC/NDF ratio of 1.82 improved growth performance, meat quality, and muscle fiber architecture in Tibetan sheep.
- Epigenetic changes were localized in distal intergenic regions, with MEF2 and SIX binding sites enriched in upregulated enhancers.
- RNA-seq confirmed that epigenetic modifications are functionally linked to pathways like fatty acid metabolism and macrophage chemotaxis.

## Abstract

We investigated epigenetic mechanisms underlying muscle development in black Tibetan sheep fed different dietary ratios of non-fiber carbohydrate to neutral detergent fiber (NFC/NDF), integrating phenotypic analyses (growth performance, meat quality, muscle histomorphology) with multi-omics approaches (ATAC-seq, H3K27ac CUT&Tag, RNA-seq).

The subjects were 2-month-old weaned male Tibetan sheep with an initial body weight of 10.45 ± 0.96 kg. Using a completely randomized study design, 90 sheep were randomly assigned to three treatment groups with 30 sheep per group. Each treatment group consisted of 5 pens with 6 sheep per pen. The dietary NFC/NDF ratios of these three treatment groups were 0.71 (Group L), 1.16 (Group M) and 1.82 (Group H).

An NFC/NDF ratio of 1.82 yielded optimal growth performance with increased live weight, carcass weight, and dressing percentage. This ratio significantly improved meat tenderness, water-holding capacity, and pH values while reducing hardness and chewiness, accompanied by compact muscle fiber architecture. Epigenomic analyses revealed epigenetic signals predominantly localized within distal intergenic regions (10–100 kb). Enhancers showed dynamic responsiveness to dietary NFC/NDF changes, with MEF2 and SIX transcription factor binding sites enriched in upregulated enhancers. RNA-seq confirmed functional associations between epigenetic modifications and gene expression, revealing enrichment of fatty acid metabolism, epithelial cell proliferation, and macrophage chemotaxis pathways. Differential expression of key genes (EGR3, FGF7, HPGD, C5, EDNRB) corroborated MEF2 and SIX families’ central role in nutrient-mediated muscle remodeling.

These findings elucidate how dietary NFC/NDF ratios optimize muscle development through enhancer activation, providing insights for precision nutrition strategies in livestock production.

Flowchart showing an experiment with ninety Tibetan sheep divided into three groups with NFC/NDF ratios of 0.71, 1.16, and 1.82 over thirty days. The process includes determination of meat quality, epigenomics, and transcriptomics. Optimal muscle development occurs at a ratio of 1.82, associated with increased MEF2 and SIX family activity, enriched in muscle development-related pathways.