FIGURE 4

Electron microscopy images of the fins reveal small round cells in the subsuperficial layer of the epidermis. (A,B,D–G) TEM images of a cross section through the epidermis of the fin. Total number of images considered = 100, 11 HCS-cells identified, for each HCS-cell up to 5 sections imaged. (A,B) The epidermis is composed of several layers of keratinocytes (Ker); the top layer being called pavement cells (PVC) with microplicae. Underneath the pavement cell layer, small round cells resemble HCS-cells. Bm: basement membrane. Col: collagen of the dermis. (A’,B’) Higher magnification of the putative HCS-cells. The cells contain a large nucleus (nuc) relative to their size, a Golgi apparatus (Ga), mitochondria (m) and vesicles (v). Unlike adjacent cells, the HCS-cells do not have desmosomes (d), however they are in contact with nerve fibers (n). (C) SEM image of the fin surface. The pavement cells (PVC) are covered with ridges called microplicae. N = 4 (D–G) Enlargement of features of HCS-cells in panels (A’,B’): Golgi apparatus (D), Nerve fiber adjacent to HCS cell and vesicle in the cytoplasm of HCS cell (E), large mitochondria (F), Neuronal projection touching HCS cells (G).