The crosslinked envelope of the keratinocyte is formed in the last stage of its terminal differentiation. This envelope is
made up of membrane and cytosolic proteins crosslinked by glutamyl lysine isopeptide bonds. The most abundant
component is involucrin, a keratinocyte protein that appears first in the cytoplasm but ultimately becomes crosslinked to
membrane proteins by transglutaminase.
NCBI Summary:
Involucrin, a component of the keratinocyte crosslinked envelope, is found in the cytoplasm and crosslinked to membrane proteins by transglutaminase. This gene is mapped to 1q21, among calpactin I light chain, trichohyalin, profillaggrin, loricrin, and calcyclin.
vanWezel IL et al reported that involucrin, a marker of keratinocyte differentiation, was localized to the
suprabasal region of the membrana granulosa of healthy follicles, particularly
in the second and third cellular layers in from the follicular basal lamina.
Conversely, the staining intensity for the intermediate filament protein
vimentin was lowest in this region, and greatest in the more antral and basal
regions. In atretic follicles, there was widespread staining for involucrin
and vimentin throughout the membrana granulosa.