Abstract
Epidermal structures are different among body sites, and proliferative keratinocytes in the epidermis play an important role in the maintenance of the epidermal structures. In recent years, intravital skin imaging has been used in mammalian skin research for the investigation of cell behaviors, but most of these experiments were performed with rodent ears. Here, we established a non-invasive intravital imaging approach for dorsal, ear, hind paw, or tail skin using R26H2BEGFP hairless mice. Using four-dimensional (x, y, z, and time) imaging, we successfully visualized mitotic cell division in epidermal basal cells. A comparison of cell division orientation relative to the basement membrane in each body site revealed that most divisions in dorsal and ear epidermis occurred in parallel, whereas the cell divisions in hind paw and tail epidermis occurred both in parallel and oblique orientations. Based on the quantitative analysis of the four-dimensional images, we showed that the epidermal thickness correlated with the basal cell density and the rate of the oblique divisions.
Highlights
Division of the basal cells in adult mammalian epidermis is important for maintenance of the epidermal structure, as these cells play a role in replenishing eliminated keratinocytes
R26H2BEGFP mice, in which a histone 2B (H2B) and enhanced green fluorescent protein (EGFP) fusion protein is expressed in the nuclei of all cells under the ubiquitous ROSA26 promoter [26], are useful for the visualization of cellular behaviors
A near-infrared laser light for two-photon excitation can alleviate the influence of scatter, and finer images than the images achieved by confocal microscopy could be obtained, even in the deepest layer of the thick epidermis and the dermis (S6 Fig)
Summary
Division of the basal cells in adult mammalian epidermis is important for maintenance of the epidermal structure, as these cells play a role in replenishing eliminated keratinocytes. Adult epidermal structures differ depending on the body site. Dorsal and ear epidermis are structurally similar and consist of only 3–5 layers [4, 5]. In paw epidermis, both the suprabasal compartment and the cornified layer are relatively thicker than the dorsal and ear epidermis. The epidermal structure in each body site is basically maintained after maturation. An epidermal homeostasis model was proposed, with the assumption that the basal cell number is constant
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