Ultrastructural pattern of loricrin localization in the epidermis of the red kangaroo Macropus rufus (Marsupialia, Mammalia) in relation to the formation of the stratum corneum in mammalian epidermis

The ultrastructural immunolocalization of loricrin, a major protein of the cell corneous envelope is known for the epidermis of monotremes and placentalmammals, but not in the soft epidermis ofmarsupials. This information would allow a definitive generalization on the role of loricrin in the process of keratinization in mammalian epidermis. The present study on the hairy epidermis of the red kangaroo has shown that the immunolabelling for this protein is diffuse in the upper spinosus layer and is peripherally associated with keratohyalin granules in the granular layer. Immunolabelling, however, is poor or absent in the darker part of keratohyalin granules which likely contains pro-filaggrin and filaggrin. In transitional and corneous cells, loricrin concentrates along the forming cell corneous envelope as in the hairy epidermis of other mammals. However, in the softer part of the corneous layer, rich in lipids, the labelling tends to disappear. Loricrin therefore appears to be connected with the strengthening of the cell corneous envelope of mature corneocytes, but becomes poorly detected in soft corneocytes. Based on the present and previous information, the distribution of loricrin in the epidermis of different mammals and in the epidermis of birds and reptiles is discussed.