Keratins and Corneous β-Proteins Expressed During Tail Regeneration in the Wall Lizard <i>Podarcis muralis</i> Re-establish the Epidermal Barrier (review)

The present review summarizes information on epidermal proteins produced during tail regeneration in the European wall lizard Podarcis muralis. The formation of new scales initiates with invagination of epidermal pegs in the regenerating epidermis closer to normal tail scales. Inside the pegs, new β- and α-corneous layers, like in normal scales, are formed. Intermediate filament keratins (IFKs or α-keratins) of few types are highly expressed and accumulate in the regenerating epidermis of blastema-cones 2 – 5 mm long. The initial proteins expressed in the apical epidermis belong to IFKs of type I (49 – 51 kDa of MW such as k19, k24 etc.), and a lower amount of types II (57 – 63 kDa) with a low content in glycine (5 – 9%) and cysteine (4 – 7%). Two keratins with unusual high MW, 76 and 130 kDa, are possible precursors of some IFKs. In more proximal regions of 3 – 5 mm long cones, where epidermal pegs are forming, a high expression of some CBPs genes (Corneous Beta Proteins, formerly termed β-keratins) and their coded proteins (14 – 25 kDa of MW) give rise to the hard β-layer of regenerated scales. CBPs are glycine-rich (18 – 29%) and relatively low in cysteine content (4 – 7%). The IFKs initially produced and later also CBPs, together minor component corneous, enzymatic and anti-microbial proteins and peptides, allow re-establishment of the original epidermal barrier of scales. The numerous proteins (and lipids) protects the skin and body from excessive transpiration, mechanical insults, chemical and microbial agents and allows tail regeneration in lizards.