Animal Molecular Breeding, 2025, Vol.15, No.2, 60-71 http://animalscipublisher.com/index.php/amb 67 expression by microRNA is a classic case. Zhang et al. (2021) found in chicken muscle cells that miR-27b-3p can complement the mRNA of the MSTN gene, thereby inhibiting MSTN translation. They verified through dual fluorescence reporter experiments that MSTN is the direct target gene of miR-27b-3p. Further cellular function assays showed that upregulation of miR-27b-3p significantly promoted the proliferation of primary cells of chicken skeletal muscle (myoblasts) and inhibited their premature differentiation. This is consistent with the effect of inhibiting MSTN: because MSTN usually limits myocyte count through cell cycle inhibition and prodifferentiation signals, miR-27b-mediated decrease in MSTN cancels a portion of the inhibition, and cells therefore proliferate more. This case clearly demonstrates how miRNAs affect muscle development by acting on specific genes. For ducks, given that the function of MSTN is highly conserved in vertebrates, it can be inferred that similar regulatory axes exist in duck muscle cells (Miretti et al., 2013). For example, if the duck's miR-27 family members are highly expressed in skeletal muscle, they are likely to also target MSTN, thereby regulating the growth rate and muscle fiber size of the duck's muscle. Future studies can perform miRNA sequencing on duck muscle tissue, identify miRNAs associated with the MSTN pathway and verify their function. If miRNAs like miR-27b-3p that have significant regulatory effects on MSTN are found in ducks, then increasing the expression of this miRNA through molecular breeding methods or inhibiting the mRNA of MSTN through antisense oligonucleotide technology will be expected to obtain more muscle-developed duck species. 6.3 lncRNA-FeatherLnc regulates feather pigmentation The color of feathers is determined by the deposition of biopigments (mainly melanin and flavonoids, etc.) in the feathers. The formation process is complex and regulated by multiple genes. In recent years, the role of long-chain non-coding RNA in the regulation of pigment deposition has been gradually revealed. A representative case is skin melanin deposition in black-feathered chicken species. Zhang et al. (2022) identified a lncRNA that plays an important role in the melanin deposition process, named LMEP. In black-feathered chicken skin, LMEP is highly expressed, which promotes upregulation of pigment synthases such as tyrosinase (TYR) through interaction with proteins related to melanin production pathway, resulting in an increase in melanin content (Figure 3). This study provides an example for understanding lncRNA regulating feather/skin pigmentation. Among ornamental duck varieties, lncRNA regulation technology can be used to cultivate new varieties with specific patterns. In production practice, the color of the feather also affects the value of the commodity. For example, all white feathers are beneficial to the appearance of the carcass. If a certain lncRNA is found to inhibit melanin deposition, it can be considered to enhance its expression to cultivate white feather varieties (Li et al., 2024). Of course, feather pigmentation is a complex trait, and it also involves multiple links such as enzyme activity and pigment transport. lncRNA is just one link. Figure 3 Histomorphological examination of YS and BS in Xichuan black chicken. Differences in skin melanination and histomorphology between YS (a) and BS (b). Arrows indicate melanin (Adopted from Zhang et al., 2022) 7 External Factors Affecting the Epigenetic Status of Ducks 7.1 Programming epigenetic states by the embryonic environment 7.1.1 Effects of temperature changes on DNA methylation and feather development Embryo development is highly sensitive to temperature, and temperature changes not only affect development speed, but may also leave "memory" through epigenetic pathways. In duck embryos, it was found that increasing the incubation temperature from 37.8 °C to 38.8 °C will upregulate the expression of methylation-related genes
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