Fluorescein-isothiocyanate as a stain for keratinizing epithelia

Identification of a major keratinocyte cell envelope protein, loricrin

During epidermal cell cornification, the deposition of a layer of covalently cross-linked protein on the cytoplasmic face of the plasma membrane forms the cell envelope. We have isolated and characterized cDNA clones encoding a major differentiation product of mouse epidermal cells, which has an amino acid composition similar to that of purified cell envelopes. Transcripts of this gene are restricted to the granular layer and are as abundant as the differentiation-specific keratins, K1 and K10. An antiserum against a C-terminal peptide localizes this protein in discrete granules in the stratum granulosum and subsequently at the periphery of stratum corneum cells. Immunofluorescence and immunoelectron microscopy detect this epitope only on the inner surface of purified cell envelopes. Taken together, these results suggest that it is a major component of cell envelopes. On the basis of its presumed function, this protein is named loricrin.

Relationship between cell differentiation and binding of fluorescein isothiocyanate (FITC)-conjugated insulin of keratinocytes in culture

Basal-type keratinocytes, isolated from newborn rat skin and separated on Percoll density gradients, proliferate in low (0.1 mM) calcium medium and, after raising the calcium level to normal (1.96 mM), stratify. Cells in the low calcium culture do not have extensive cell-cell connections, as seen with fluorescein isothiocyanate (FITC)-conjugated insulin. Fluorescein isothiocyanate-conjugated concanavalin A and Griffonia simplicifolia isolectin B4, but not peanut agglutinin (PNA), fluorescently label these cells. In 3-day-old low calcium cultures, within 2 h after raising the calcium of the medium to the normal level, intense binding of PNA to cells appears and neighboring cells are connected through bundles of filaments that are fluorescently labeled by FITC-insulin. After 2 days in normal calcium medium, the cultures exhibit relatively smooth, straightlined, cell boundaries that are labeled by FITC-insulin and cell boundaries and intracellular granules that are stained by hematoxylin. One day later, similar cell boundaries are present, but they are not significantly decorated by FITC-insulin and, under phase contrast microscopy, are dark. Free FITC gives labeling patterns similar to those given by FITC-insulin, but the FITC labeling is blocked by mercaptoethanol and dithiothreitol in contrast to FITC-insulin binding. The present results suggest the insulin moiety is involved in the labeling by FITC-insulin and the labeling is chronologically related to the stage of cell differentiation.

Immunofluorescent tracing of cytoplasmic components involved in keratinocyte differentiation

Sera with epidermal cytoplasmic antibodies (E.C.A.) produced by human subjects after bone marrow transplantation have been studied by indirect immunofluorescen on rabbit lip sections. These sections were used in order to give on a single specimen, areas of mucosa, of parakeratotic and of orthokeratotic epithelium. It has been demonstrated that E.C.A. distinguished the basal cell layer from the upper cell layers on the three areas. Moreover, E.C.A. were not found to react identically on mucosal, parakeratotic and orthokeratotic epithelium. These findings strongly suggest that the target antigens for E.C.A. are molecules involved in keratinocyte differentiation.

"Keratolytic" effect of salicylic acid

The "keratolytic" effect of salicylic acid was examined in guinea-pig skin. Using a fluorescent staining method the str. corneum cells could be seen to rapidly become detached. The cellular walls remained unchanged. This drug therefore appears to primarily reduce the intercellular cohesiveness of the horny cells.