Occurrence of Melanosome-Containing Merkel Cells in Mammalian Oral Mucosa

Abstract

The occurrence and fine structure of Merkel cells with melanosomes in the labial epithelium of the dog and cat were studied by electron microscopy. These melanosomes were polarized in the Merkel cell cytoplasm opposite to the major aggregation of dense-cored granules and the closely abutting nerve terminal. None of melanosomes was found in the Golgi complex region where a few immature dense-cored granules were observed. This may suggest that the melanosomes are not produced in the Merkel cell, but are taken from the melanocytes like in keratinocytes. The possible phagocytotic ability of Merkel cells is discussed.

Ultrastructural characterization of normal Merkel cells in the dog

“…Langerhans cells and melanocytes lack tonofilaments, desmosomes, association with nerve terminals and the characteristic MK granules . Few MKs containing melanosomes were detected in the nasal planum and lip epithelium in our study, similar to MKs in other mammals . These melanosomes appeared mature and were located in the apical cytoplasm, opposite the major accumulation of dense‐core granules.…”

“…These melanosomes appeared mature and were located in the apical cytoplasm, opposite the major accumulation of dense‐core granules. The absence of immature melanosomes and the identification of membrane‐bound melanosomes indicate that they are transferred from surrounding melanocytes by a similar mechanism to that described for keratinocytes …”

Merkel cells: A collective review of current concepts

“…[ 30 ] The cells have a distinctive intranuclear rodlet and vesicles. [ 18 ] Sometimes, MCs contain melanosomes that are taken from the melanocytes similar to keratinocytes[ 31 ] [ Figure 2 ].…”

Merkel cells

“…The melanosomes appear bigger and darker than dense core granules and are on the opposite side of the cytoplasm, with clear vesicles. 13,63 The presence of these structures needs further explanation.…”