Histology and ultrastructure of transitional changes in skin morphology in the juvenile and adult four-striped mouse (Rhabdomys pumilio)

Abstract

The four-striped mouse has a grey to brown coloured coat with four characteristic dark stripes interspersed with three lighter stripes running along its back. The histological differences in the skin of the juvenile and adult mouse were investigated by Haematoxylin and Eosin and Masson Trichrome staining, while melanocytes in the skin were studied through melanin-specific Ferro-ferricyanide staining. The ultrastructure of the juvenile skin, hair follicles, and melanocytes was also explored. In both the juvenile and adult four-striped mouse, pigment-containing cells were observed in the dermis and were homogeneously dispersed throughout this layer. Apart from these cells, the histology of the skin of the adult four-striped mouse was similar to normal mammalian skin. In the juvenile four-striped mouse, abundant hair follicles of varying sizes were observed in the dermis and hypodermis, while hair follicles of similar size were only present in the dermis of adult four-striped mouse. Ultrastructural analysis of juvenile hair follicles revealed that the arrangement and differentiation of cellular layers were typical of a mammal. This study therefore provides unique transition pattern in the four-striped mouse skin morphology different from the textbook description of the normal mammalian skin.

Figure 1

Photomicrographs of striped dorsal skin from the four-striped mouse. (a), (c), and (e) are adult skin and (b), (d), and (f) juvenile skin. Hair follicles are present in the dermis of both the adult (left) and juvenile (right). However, a marked difference is visible in the hypodermis of the juvenile containing abundant hair follicles of varying sizes (right), whereas the adult has none (left). Note the epidermis (line), dermis (bracket), hypodermis (double arrow), and hair follicles (arrows). (a) and (b) Haematoxylin and Eosin staining. (c) and (d) Masson Trichrome staining. (e) and (f) Ferro-ferricyanide staining. Scale bar (a)–(f): 10 μm.

Figure 2

Photomicrographs of dermis from dorsal skin of the four-striped mouse. Pigment-containing cells (arrow) are homogeneously dispersed throughout the dermis. (a) Adult and (b) juvenile. Haematoxylin and Eosin, scale bar (a) and (b) = 2.5 µm.

Figure 3

Pigment-containing cells in the four-striped mouse skin. (a), (c), and (e) from adult skin and (b), (d), and (f) from juvenile skin. Pigment-containing cell (p) is interspersed between connective tissue in (a)–(d). Pigment-containing granules are visible in the cell cytoplasm surrounding the nucleus (n) and in the long cytoplasmic extensions (e) and they also lie between adipocytes (f). (a) and (b) are photomicrographs of adult and juvenile dermis, respectively. (c) is electron micrograph of adult dermis; (d) is juvenile dermis; (e) adult hypodermis, and (f) juvenile dermis. a: adipocyte; c: collagen; cp: capillary; m: mast cell. (a) and (b) are Toluidine blue staining and scale bar = 1 µm. Scale bar: (c) = 0.33 µm; (d) = 0.5 µm; (e) = 0.33 µm; (f) = 0.17 µm.

Figure 4

Hair follicles in the dermis of an adult four-striped mouse. Photomicrograph of multiple hair follicles (a) and electron micrograph of a single hair follicle (b). hs: hair shaft; ors: outer root sheath; s: sebaceous gland. (a) is Toluidine blue staining and scale bar = 2.5 µm. (b) is an electron micrograph and with scale bar = 0.33 µm.

Figure 5

Photomicrograph of the hair follicles in the young adult four-striped mice at different levels. (a) and (b) are at the hair bulb level. (a) shows two hair follicles of small and intermediate sizes. (b) is a large follicle compared to (a). (c) shows a large follicle sectioned at the suprabulbar level, in the hypodermis. (d) is a large follicle at a level slightly higher than the suprabulbar level, in the hypodermis. (e) is follicles, in the superficial hypodermis to basal dermis. (f) shows follicles in the dermis at, or above, the sebaceous gland. A: adipocytes; Cc: cuticle of cortex; Ci: cuticle of inner root sheath; Cp: companion layer; Ctf: connective tissue follicle; Cx: cortex; D: dermis; Dp: dermal papilla; He: Henle's layer; Hm: hair matrix; Hs: hair shaft; Hx: Huxley's layer; Irs: inner root sheath; M: medulla; Ors: outer root sheath; S: sebaceous gland. Toluidine blue staining. Scale bar: 50 µm.

Figure 6

Electron micrographs of hair follicles from young adult four-striped mouse skin. (a) and (b) correspond to Figures 5(a) and 5(b) at the hair bulb and suprabulbar levels. Trichohyalin granules (arrows) are seen in the Huxley and Henle layers. (c) is at the suprabulbar level showing an accumulation of cells in Huxley's layer in the superior aspect of the follicle and corresponds to Figure 5(c). (d) is a section slightly higher than suprabulbar level and corresponds to Figure 5(d). Henle's layer and the inner root sheath are keratinised. (e) is a section of hair follicle layers at the superficial hypodermis to basal dermis and corresponds to Figure 5(e). The inner root sheath is fully keratinised in (f) above the level of the sebaceous gland and corresponds to Figure 5(f). Bm: basement membrane; C: collagen fibres; Cc: cuticle of cortex; Ci: cuticle of inner root sheath; Co: cornified cellular layer; Cp: companion layer; CTF: connective tissue follicle; Cx: cortex; DP: dermal papilla; He: Henle Layer; Hx: Huxley layer; ORS: outer root sheath; Line; hair matrix; Asterisk; area of missing hair shaft. Scale bar: (a) and (d), 0.5 µm; (b) and (c), 0.33 µm, (e), 0.25 µm and (f), 0.20 µm.