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Single cell transcriptomics defines keratinocyte differentiation in avian scutate scales

ABSTRACT: Epidermal keratinocytes form cornified skin appendages such as scutate scales on the legs of birds. Here, we investigated the molecular pathways of keratinocyte differentiation in chicken scutate scales by single cell transcriptomics. We identified two distinct populations of differentiated keratinocytes. The first type of differentiated keratinocytes is characterized by mRNAs encoding scale-type corneous beta-proteins (CBPs), also known as beta-keratins and cysteine-rich keratins, indicating that these cells form hard scales. The second type of differentiated keratinocytes contains mRNAs encoding keratinocyte-type CBPs and cysteine-poor keratins, indicating that these cells form the soft interscale epidermis. Immunostaining with a newly raised antibody confirmed that keratin 9-like cysteine-rich 2 (KRT9LC2) or Hard Acid Sauropsid-specific 2 (HAS2) keratin, which is a marker of the first type of keratinocytes, is expressed in the suprabasal epidermal layers of scutate scales but not in interscale epidermis. Furthermore, mRNA of CTNN1B, previously implicated in scale placode formation, was enriched in differentiated scale keratinocytes, whereas genes involved in lipid metabolism, such as ELOVL4 and FADS1 were enriched in keratinocytes of the interscale epidermis. In conclusion, this study defines the gene expression programs that build the scutate scales and interscale epidermis of birds.

ORGANISM(S): Gallus gallus

PROVIDER: GSE179690 | GEO | 2021/07/09

REPOSITORIES: GEO

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Project description:Nails protect the soft tissue of the tips of digits in humans. In birds and mammals the equivalent claws are used for purposes including capturing prey, digging, climbing, fighting and maintaining dexterity and balance. The molecular mechanism of nail (and claw) development is largely unknown, but we have recently identified a Wnt receptor gene, Frizzled6 (Fzd6), as mutated in a human autosomal-recessive nail dysplasia. To investigate the action of Fzd6 in claw development at the molecular level, we compared gene expression profiles of digit tips of wild-type and Fzd6-/- mice, and show that Fzd6 regulates the transcription of a striking number of epidermal differentiation-related genes. Sixty-three genes encoding keratins, keratin associated proteins, and transglutaminases and their substrates were significantly down-regulated in the knockout mice. Among them, four hard keratins, Krt86, Krt81, Krt34 and Krt31; two epithelial keratins, Krt6a and Krt6b; and transglutaminase1 were known to be expressed in nails and involved in nail abnormality when dysregulated. Immunohistochemical studies revealed decreased expression of Krt86, Krt6b and involucrin in the epidermal portion of the claw field in the knockout embryos. We further show that Dkk4, a Wnt antagonist, was significantly down-regulated in Fzd6-/- mice along with Wnt, Bmp and Hh family genes; and Dkk4 transgenic mice showed a subtly but appreciably modified claw phenotype. Thus, Fzd6-mediated Wnt signaling likely regulates the overall differentiation process of nail/claw formation. Heterozygous Fzd6+/- mice (kindly provided by Dr. J. Nathans) were crossed to generate Fzd6+/-, Fzd6-/- and wild-type offspring. Timed matings were set up to harvest embryos at E14.5, E16.5 and E18.5. The morning after mating was designated as E0.5. Tails and the digital tips from forelimbs of three wild-type and Fzd6-/- mice from each embryonic time-point were excised, immediately frozen on dry ice, and stored at 80 C freezer until use. Genotyping was done as described previously (15). RNA was extracted using Trizol Reagent (Life technologies). RNA from dissected forelimbs from each embryo of the three time-points was used for microarray analysis.

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Single cell transcriptomics defines keratinocyte differentiation in avian scutate scales

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