Animal Molecular Breeding, 2025, Vol.15, No.2, 60-71 http://animalscipublisher.com/index.php/amb 64 maturation of muscle fibers. Secondly, histone modification is also important in regulating muscle growth genes. The promoters of muscle differentiation markers are usually accompanied by an increase in activated histone markers, while cell cycle genes obtain inhibitory markers when differentiated. Such epigenetic "switches" ensure that myocytes exit proliferate and enter differentiation in time. In duck muscle development, similar histone modification regulatory mechanisms can be speculated to exist. Again, non-coding RNAs are involved in epigenetic regulation of muscle development. Many miRNAs are rich in expression in muscle tissue and have specific developmental stages. For example, miR-206, miR-133, etc. are significantly upregulated during the embryonic muscle differentiation period, helping to promote myotubes. Epigenetics is also a key regulator of fat deposition. The formation of adipose tissue is regulated by peroxisome proliferator-activated receptor (PPAR) pathways, and epigenetics can affect the activity of these genes. From the late stage of duck embryos to fattening, the regulation of expression of lipid metabolism genes in the liver and muscle is associated with changes in DNA methylation/demethylation. Recent studies have parsed the mRNA N6-methyladenine (m6A) modification map of duck embryonic muscle tissue for the first time, and found that m6A RNA methylation can affect fatty acid β oxidation and lipid metabolism-related pathways, thereby regulating fat deposition (Gu et al., 2022). m6A is an emerging epigenetic mechanism that regulates gene function by affecting mRNA stability and translation efficiency, showing an important role in duck muscle and fat development. 4.3 The influence of environmental factors on the epigenetic status of growth What is unique about epigenetics is its plasticity, and environmental factors can have a lasting impact on gene function through epigenetic pathways. During the growth of a duck, the external environment (including the embryonic and growth stage environment) will "program" its epigenetic state. Embryo phase temperature is a typical factor. Appropriate incubation temperatures are essential for normal development, and temperature deviations from the optimal range can cause an embryonic epigenetic response. Studies have shown that increasing the temperature of avian embryos by 1 °C will change the embryonic development rhythm and induce dynamic changes in DNA methyltransferase gene expression. In duck embryo tests, higher than normal hatching temperatures have been shown to significantly increase the activity of enzymes such as DNMT1 and DNMT3A in the embryo muscles and liver (Yan et al., 2015), indicating that temperature rise activates the embryonic epigenetic enzyme system, which may lead to changes in genome-wide methylation levels. This temperature-induced epigenetic change may have long-term effects on the growth of duck chicks after hatching, such as better heat tolerance but decreased weight gain. Nutritional level is also an important environmental factor. Nutrients (such as folic acid, choline, vitamin B12, methionine, etc.) can provide methyl donors, which directly affects the DNA methylation process. In poultry, both maternal nutrition and nutrient injections during incubation may alter the epigenetic status of the embryo. Stress factors (such as high temperature, density, transportation, etc.) also affect growth through epigenetic effects during the growth period of ducks. Long-term heat stress can lead to imbalance of stress axis hormones in ducks, and it is accompanied by changes in promoter methylation of stress-related genes (such as HSP heat shock protein gene), causing adaptive adjustments to the stress response ability of ducks to only high temperatures (Massimino et al., 2021). In addition, the impact of the microbial environment on growth is becoming increasingly important. Intestinal flora can produce metabolites such as short-chain fatty acids, which can change the histone acetylation state of the host liver and muscle cells by inhibiting histone deacetylation enzymes, thereby regulating the expression of metabolic genes. 5 Epigenetic Regulation of Duck Feather Development 5.1 Gene regulation in feather formation and growth Feather formation is a highly programmed developmental process that requires precise gene regulation networks. The most in-depth research is the role of various signaling pathways in feather follicle morphogenesis. In chicken feather development models, the Wnt signal is considered as the first signal to initiate feather primordial formation; subsequent Eda (ectodermal development factor) and FGF (fibroblast growth factor) signals induce dermal papillary aggregation; BMP signal acts as antagonist to limit the size and interfoetal width of the primary
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