Loricrin‐like immunoreactivity during keratinization in lizard epidermis

Abstract

Two modalities of keratinization are present in lizard epidermis: alpha (soft-pliable corneous layers) and beta (hard and inflexible corneous layers). While beta-keratinization is probably due to the synthesis of a new (beta)-keratin gene product, alpha keratinization resembles in part that of mammalian epidermis. The goal of this study was to test whether a sulfur-rich molecule similar to the mammalian corneous cell envelope protein loricrin is also present in lizard epidermis. This was done using X-ray microanalysis and immunocytochemical and ultrastructural methods. In the epidermis of the lizard Podarcis muralis small (0.1-0.3 microm) to large (1-5 microm) keratohyalin-like granules (KHLGs) are produced in alpha-keratinizing cells, especially in the clear layer. Small KHLGs contain sulfur and show weak filaggrin-like and stronger loricrin-like immunoreactivities. The latter is also present in keratinizing alpha-layers but is absent in the beta layers. Large KHLGs in the clear layer derive from the aggregation of the small granules with other components, including lipid material. These large granules show some loricrin-like immunoreactivity and contain sulfur and phosphorous, histidine, but not filaggrin-like immunoreactivity. It is suggested here that phosphorous derives from their phospholipid component. The present study shows that the modality of alpha-keratinization of lizard epidermis resembles that of mammals and suggests that the basic molecular mechanisms of keratin aggregation and formation of the corneous cell envelope were already present in the therapsid line of reptiles from which mammals evolved.

Formation of the corneous layer in the epidermis of the tuatara (Sphenodon punctatus, Sphenodontida, Lepidosauria, Reptilia)

“…The latter protein makes up a large proportion of the cornified cell envelope of fully differentiated mammalian keratinocytes (Fuchs 1990;Mehrel et al 1990). Although very little is known about sulfur-rich proteins in reptilian keratinocytes, it is known that small keratohyalin-like granules in lizard keratinocytes give some immuno-cross-reactivity to loricrin and filaggrin (Alibardi 2002b(Alibardi , 2003.…”

Reptile scale paradigm: Evo-Devo, pattern formation and regeneration

“…Reptiles have both α-and β-keratins. α-keratogenic tissue provides a barrier to water loss while an overlying β-keratogenic layer provides mechanical stiffness to the skin (Alexander, 1970; Baden et al ., 1970, 1974; Fraser and Parry, 1996; Gregg and Rogers, 1986; Landmann, 1986; Maderson, 1985; Presland et al ., 1989a, 1989b; Carver and Sawyer, 1987; Sawyer et al ., 2000; Steinert and Freedberg, 1991; Alibardi et al ., 2002, 2005; Alibardi, 2000, 2001, 2002a, 2002b; Alibardi and Toni, 2006; Wyld and Brush, 1979, 1983). …”

Localization and Characterization of Specific Cornification Proteins in Avian Epidermis

“…This information suggests that loricrin and complex lipids may be somehow related to each other or follow a similar intracellular pathway during their final processing. Previous studies on reptilian and avian corneocytes have shown that loricrin (and filaggrin) immunoreactivity is associated with vesicular bodies, the lipidic equivalent of mammalian lamellar bodies [Landmann, 1979[Landmann, , 1980Alibardi, 2002bAlibardi, -e, 2004a.…”