Transglutaminase Activity Is Conserved in Stratified Epithelia and Skin Appendages of Mammals and Birds

Abstract

The cross-linking of structural proteins is critical for establishing the mechanical stability of the epithelial compartments of the skin and skin appendages. The introduction of isopeptide bonds between glutamine and lysine residues depends on catalysis by transglutaminases and represents the main protein cross-linking mechanism besides the formation of disulfide bonds. Here, we used a fluorescent labeling protocol to localize the activity of transglutaminases on thin sections of the integument and its appendages in mammals and birds. In human tissues, transglutaminase activity was detected in the granular layer of the epidermis, suprabasal layers of the gingival epithelium, the duct of sweat glands, hair follicles and the nail matrix. In the skin appendages of chickens, transglutaminase activity was present in the claw matrix, the feather follicle sheath, the feather sheath and in differentiating keratinocytes of feather barb ridges. During chicken embryogenesis, active transglutaminase was found in the cornifying epidermis, the periderm and the subperiderm. Transglutaminase activity was also detected in the filiform papillae on the tongue of mice and in conical papillae on the tongue of chickens. In summary, our study reveals that transglutaminase activities are widely distributed in integumentary structures and suggests that transglutamination contributes to the cornification of hard skin appendages such as nails and feathers.

The Evolution of Transglutaminases Underlies the Origin and Loss of Cornified Skin Appendages in Vertebrates

“…An in situ TGM activity assay combined with immunofluorescence was performed based on a published protocol ( Sachslehner et al 2023 ). The samples were encircled with a liquid blocker (Daido Sangyo Co. Ltd.) and subsequently incubated with 2% bovine serum albumin (BSA, Sigma-Aldrich) in phosphate-buffered saline (PBS) with 0.05% Tween at room temperature for 30 min.…”

“…Epidermal cornification is diminished or modified at the subcellular level in mammals that have secondarily acquired a fully aquatic lifestyle (cetaceans and sirenians) ( Ehrlich et al 2019 ; Menon et al 2022 ). Hard skin appendages, such as hair, claws, and feathers, are cornified by transglutamination ( Sachslehner et al 2023 ) and by the formation of disulfide bonds ( Strasser et al 2015 ; Harland and Plowman 2018 ; Ehrlich et al 2020 ). The cornified epithelial egg tooth, also known as caruncle, is conserved in many but not all amniotes ( Mlitz et al 2021 ; Fenelon et al 2023 ).…”

Cornification of keratinocytes is associated with differential changes in the catalytic activity and the immunoreactivity of transglutaminase-1

“…Primary human keratinocytes grown on chambered cell culture slides (catalogue number 354118, Falcon, NY, USA) and a diluted cell suspension of transfected HEK293T cells prepared by cytospin were fixed on the slides using 100% methanol at −20 °C for 30 min, air dried and stored at −20 °C or stained immediately. An in situ transglutaminase activity assay combined with immunofluorescence was performed based on published protocols 30,[49][50][51] . Cryosections of human skin were thawed at room temperature for 10 min before they were placed in PBS for 5 min at room temperature to remove remaining OCT compound from the slides.…”

Iron Metabolism of the Skin: Recycling versus Release

“…The epidermis of the skin is connected to other stratified epithelia that cover the oral cavity, the esophagus, and the vagina. These epithelia are not covered by a cornified layer in humans, but several differentiation steps are similar to those of the epidermis [ 106 , 107 ]. This similarity includes the expression of Hmox1 , which was reported in the uppermost layers of the tongue, esophagus, and forestomach [ 54 ].…”