Abstract
Sciellin is a precursor of the cornified envelopes of mammalian keratinizing tissues. We have cloned the cDNA encoding sciellin by screening a human keratinocyte expression library with a sciellin-specific monoclonal antibody. The composite cDNA of 2.35 kilobase pairs encodes a protein of 75.3 kDa with a pI of 10.09. The translated sequence has a central domain containing 16 repeats of 20 amino acids each that is rich in Gln and Lys residues, which are potential transglutaminase substrates, and a carboxyl domain, which contains a single LIM motif. Sciellin cDNA probes hybridize to bands of 3.4 and 4.4 kilobase pairs on Northern blots of cultured human keratinocyte RNA. The gene was mapped to human chromosome band 13q22 by fluorescence in situ hybridization. Radiation hybrid mapping demonstrated that sciellin is linked to the sequence tagged site marker WI-457 with a logarithm of the odds score of 7.77. In situ hybridization of human foreskin tissue sections demonstrated that sciellin is expressed in the stratum granulosum. Immunofluorescent staining with a polyclonal rabbit antibody made to a recombinant sciellin protein showed peripheral cytoplasmic localization in the upper cell layers of epidermis and in stratified squamous epithelia such as the oral cavity, esophagus, and vagina. Simple and columnar epithelia, with the exception of the amnion, showed no reaction.
Highlights
The cornified envelope is a 15-nm-thick insoluble protein layer that is formed under the plasma membrane in the upper layers of epidermis and keratinizing stratified epithelium [1]
CDNA Cloning—A human foreskin keratinocyte expression library was screened with a mouse monoclonal antibody (34D11) specific for the cornified envelope precursor sciellin
We report here the cDNA cloning and characterization of sciellin, a novel cornified envelope precursor isolated from human keratinocytes
Summary
The cornified envelope is a 15-nm-thick insoluble protein layer that is formed under the plasma membrane in the upper layers of epidermis and keratinizing stratified epithelium [1]. It appears to play a major role in the physical barrier properties of the stratum corneum [2]. Loricrin is believed to form a meshlike scaffold, which is flexible as a result of its high glycine content and insoluble due to disulfide bonding and transglutaminase-catalyzed cross-linking to other cornified envelope components [12]. Overexpression of human loricrin in transgenic mice resulted in no detectable phenotype, even though all of the expressed protein was incorporated into the cornified envelope [21]. Overexpression of involucrin caused abnormalities in the structure and function of the CE and hair follicles
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