Coat coloration represents one of the most diverse traits in primates, subject to selection due to its significant implications in camouflage, heat absorption, and communication. Melanism, a genetic trait leading to increased pigmentation and darker coloration, is particularly noteworthy. Among macaques, the black monkey (
M. nigra ) exhibits a fully dark coat color, distinct from other species like
M. ochreata, which display a brownish two-tone color pattern.
To elucidate the genetic mechanism of melanism in
M. nigra, we initially examined the hair root transcriptome in four individuals of both
M. nigra and
M. ochreata. We identified 350 genes with differentiated expression (DEGs) between the dark hair of
M. nigra and
M. ochreata. Notably, 263 DEGs were upregulated in
M. nigra, significantly enriched in processes such as intermediate filament organization, skin epidermis development, trabecula formation, and T cell differentiation. Several DEGs enriched in pigmentation pathways were also upregulated, including CTLA4, FOXN1, GDPD3, KRT2, KRT27, LEF1, SLC40A1, and TYRP1. Of particular interest are LEF1 and TYRP1 for their roles in the Wnt signaling pathway and tyrosine metabolism, respectively.
Furthermore, we identified a 9-bp deletion in the upstream of ASIP, which encodes a protein inhibiting melanin synthesis in
M. nigra. However, the role of this deletion in melanism in
M. nigra remains to be confirmed through additional functional assays. These findings will offer unique insights into the genetic basis of coat color variation in primates.
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