Animal Molecular Breeding, 2025, Vol.15, No.2, 60-71 http://animalscipublisher.com/index.php/amb 66 H3K27me3) or higher DNA methylation. When hair follicles enter the growth phase and stem cells begin to activate and differentiate into new feathers, their epigenetic map changes. Studies have observed in mammalian hair follicle stem cells that activation of α smooth muscle actin (α-SMA)-positive dermal papillary cells is an important link in the restart of the hair follicle cycle, and this process involves histone demethylation to open up chromatin and express specific genes of dermal papillary stem cells. In duck feather follicles, a similar mechanism can be inferred: when the rest period turns to the growth phase, some inhibitory epigenetic markers in the hair follicle stem cells are removed, and the stem cells are activated and proliferated, inducing the growth of new feathers. In addition to DNA and histone levels, epigenetics of hair follicle stem cells also involve the role of non-coding RNA. There is evidence that some lncRNAs are highly expressed in hair follicle stem cells, which may maintain stem cells undifferentiated by affecting chromatin status (Raghuwanshi et al., 2017). In addition, signals in the hair follicle microenvironment ("indomain") can also alter stem cell behavior through epigenetic. Cell-cell signals (such as BMP, FGF) at the papillary site of feathers can induce acetylation or demethylation of specific gene promoters in stem cells, thereby initiating a differentiation procedure. 5.3 Non-coding RNA regulation of feather morphology and pigmentation deposition The final morphology and pigmentation of feathers are controlled by multiple genes and are also affected by epigenetic levels such as non-coding RNA. In particular, miRNA and lncRNA have attracted increasing attention in regulating pigment cell function and keratin formation. In terms of feather pigmentation, the synthesis of melanin is determined by enzymes such as tyrosinase (TYR), tyrosinase-related proteins (TRP-1, TRP-2), and its expression in feather follicle melanocytes is subject to complex regulation. Studies have compared the skin transcriptomes of different feather colors in the hybrid offspring of ducks, and found that the expression differences of many pigment-related genes may be caused by upstream non-coding RNA. In particular, long chain non-coding RNAs play the role of "palette" in it. In addition to lncRNA, miRNA is also involved in the formation of feather pattern. It has been reported that in pupil cells with high expression of feather keratin, some miRNAs are downregulated to relieve the inhibition of the keratin gene, thereby ensuring large-scale synthesis of keratin (Dunislawska et al., 2022). If these miRNA levels are abnormal, phenotypes such as fragile feathers and structural abnormalities may appear. 6 Case Analysis 6.1 IGF1 gene methylation and growth performance improvement IGF1 gene methylation and growth performance have improved. Islet-like growth factor 1 (IGF1) is an important hormone on the growth axis and can promote the growth of bones and muscles. Improving IGF1 expression is often considered conducive to growth performance. However, the expression of the IGF1 gene is not only regulated by pituitary growth hormone, but also by the epigenetic status of its promoter region. A typical case comes from a study on "hot programming" of poultry embryos: Cong et al. (2023) conducted intermittent high-temperature treatment of broiler embryos in the middle of hatching, and found that the growth rate of broiler chickens after hatching high-temperature embryos decreased. Mechanistic analysis showed that the expression of IGF1 gene in the liver of these chickens was significantly lower than that of the control group, while the DNA methylation level in the IGF1 promoter region was significantly increased (Cong et al., 2023). That is to say, the high-temperature embryonic environment induced abnormal methylation of the IGF1 promoter, inhibiting the normal transcription of IGF1, and thus leading to growth restriction. This finding shows that by regulating the epigenetic status of the IGF1 gene, it can affect the growth performance of animals. For ducks, although no detailed studies have been conducted similarly to high temperature treatments, it is speculated that moderate environmental interventions during embryonic stage may regulate duck growth by affecting IGF1 methylation. If the "epigenetic programming" method is used, temperature/nutritional stimulation is given at a critical stage of duck embryo development, reducing the methylation of the IGF1 gene promoter, thereby promoting high IGF1 expression, which may show faster growth and higher feed conversion after incubation. 6.2 miRNA-MediatedMSTNgene expression and muscle development Myostatin encoded by the myostatin gene (MSTN) is a negative regulator that limits muscle overgrowth. The function of inhibiting MSTNsignificantly increases muscle mass. At the epigenetic level, the regulation of MSTN
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