Animal Molecular Breeding, 2025, Vol.15, No.2, 60-71 http://animalscipublisher.com/index.php/amb 65 axis of the feather. The spatial and temporal activation of these gene pathways laid the basic morphology of feathers (Ji et al., 2023). So, how does epigenetic involve it? In the chromatin state of the promoter of feather-related genes, opening or closing will determine whether the gene can be expressed in time. It is speculated that the LEF1 gene promoter may have epigenetic markers such as histone acetylation in the feather bud stage to ensure its transcriptional activity. At the same time, switching of gene expression at different stages may also be achieved through DNA methylation regulation. When a signaling pathway completes its phased operation, the rise in methylation levels of its key gene promoter can silence it, allowing the next pathway to dominate. When feather buds differentiate into feather branches (small branches), some early signals may be required, and the maintenance of this inhibition may involve DNA methylation (Chen et al., 2024). Although there is currently a lack of research on epigenetic maps during duck feather development, it is speculated based on data from other species that many genes that regulate feather morphology are also epigenetic. For example, there was a study comparing the feather tissue expression profiles of different feather color lines of ducks, and it was found that multiple genes that control feather morphology and pigment had expression differences between lines (Figure 2) (Twumasi et al., 2024). These gene expression differences are not entirely caused by mutations in the coding sequence, but are more likely to be caused by epigenetic regulation, such as promoter methylation differences or distal enhancer chromatin accessibility. Figure 2 Feather shape and color characteristics of dorsal ventral feathers. (a) Body area of the collected feathers. (b) Measurement of the left color area (LCA) and right color area (RCA) of the dorsal ventral feathers; the red shape represents the selected color area. (c) Measurement of the left color length (LCL) and right color length (RCL) of the dorsal ventral feathers (excerpted from Twumasi et al., 2024) 5.2 Epigenetic characteristics of feather follicle stem cells There is a group of stem cells in the feather follicles located in the nipple and base areas of the hair follicle, responsible for the continuous growth and periodic regeneration of the feathers. These stem cells have the potential for multidirectional differentiation and can produce different types of cells such as feather epidermal cells, medulla cells, and feather branches. The fate decision of hair follicle stem cells is closely related to their epigenetic status. When stem cells maintain an undifferentiated state, genes related to proliferation and self-renewal in their genome remain active, while differentiation-related genes are inhibited. This is often reflected in epigenetics, i.e., the widespread presence of histone activation markers and open chromatin structures in stem cells, whereas the promoter of differentiation marker genes carries inhibitory histone modifications (such as
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