Single-Cell Transcriptomics Defines Keratinocyte Differentiation in Avian Scutate Scales

This study explored the differentiation of keratinocytes in avian scutate scales by using single-cell transcriptomics on cells from the skin of 1-day old chicks. Two distinct populations of differentiated keratinocytes were identified: one characterized by mRNAs for cysteine-rich keratins and scale-type corneous beta-proteins (CBPs), which form hard scales, and another with mRNAs for cysteine-poor keratins and keratinocyte-type CBPs, associated with the formation of soft interscale epidermis. An antibody against keratin 9-like cysteine-rich 2 (KRT9LC2), enriched in the first population, was used for immunostaining, confirming its expression in the hard scales but not in the interscale epidermis. The study also found similarities in keratinocyte differentiation between chicken leg skin and human skin, including the upregulation of epidermal differentiation complex genes and genes involved in lipid metabolism and transport, suggesting evolutionary conservation in these processes.