Re-epithelialization of cutaneous wounds in adult zebrafish uses a combination of mechanisms at play during wound closure in embryonic and adult mammals

Abstract

Re-epithelialization of cutaneous wounds in adult mammals takes days to complete and relies on numerous signalling cues and multiple overlapping cellular processes that take place both within the epidermis and in other participating tissues. Re-epithelialization of partial-or fullthickness skin wounds of adult zebrafish, however, is extremely rapid and largely independent of the other processes of wound healing. Live imaging after treatment with transgene-encoded or chemical inhibitors reveals that re-epithelializing keratinocytes repopulate wounds by TGF-β-and integrin-dependent lamellipodial crawling at the leading edges of the epidermal tongue. In addition, re-epithelialization requires long-range epithelial rearrangements, involving radial intercalations, flattening and directed elongation of cells -processes that are dependent on Rho kinase, JNK and, to some extent, planar cell polarity within the epidermis. These rearrangements lead to a massive recruitment of keratinocytes from the adjacent epidermis and make reepithelialization independent of keratinocyte proliferation and the mitogenic effect of FGF signalling, which are only required after wound closure, allowing the epidermis outside the wound to re-establish its normal thickness. Together, these results demonstrate that the adult zebrafish is a valuable in vivo model for studying and visualizing the processes involved in cutaneous wound closure, facilitating the dissection of direct from indirect and motogenic from mitogenic effects of genes and molecules affecting wound re-epithelialization.

Scanning electron microscope investigation on the process of healing of skin wounds in Cirrhinus mrigala

“…This could be considered necessary for the epithelialization to close the wound. Recent scanning electron microscope study (Richardson et al, ) reported that in Danio rerio superficial keratinocytes (=epithelial cells, present study) closer to the wound were strongly elongated in the direction of the wound and suggested that keratinocytes undergo directed and coordinated cell flattening, polarization and elongation. Sonnemann and Bement () reported in a review article that in different vertebrates and invertebrates epidermal cells, in general, near the wound edge undergo a transient dedifferentiation; assume a more flattened, elongate phenotype; and migrate into the wound area.…”

“…Scanning electron microscope (SEM) provides a means for observing and surveying the surface topography of tissue specimen and is a useful tool to reveal the details of surface architecture of tissues to an extent not possible by other procedures. Studies concerned with the SEM of healing of the skin wound, however, are relatively few (Kumari, Verma, Nigam, Mittal, & Mittal, ; Rai et al, ; Richardson et al, ; Silva et al, ).…”

Learning from regeneration research organisms: The circuitous road to scar free wound healing

“…This is an advantage because certain proteins may play different roles in each phase. For example, Fibroblasts Growth Factors are not required for re-epithelialization, but are required for later epidermal remodeling and granulation tissue formation (Richardson et al, 2016). Generation of a “skinbow” zebrafish in the Poss lab, has allowed large-scale tracking of skin cells response to injury and has enabled the identification of differences in epithelial cellular responses during normal homeostatic turnover of the skin versus minor exfoliation injuries versus regeneration of major portions of the skin.…”

“…Generation of a “skinbow” zebrafish in the Poss lab, has allowed large-scale tracking of skin cells response to injury and has enabled the identification of differences in epithelial cellular responses during normal homeostatic turnover of the skin versus minor exfoliation injuries versus regeneration of major portions of the skin. Indeed the combination of transgenic zebrafish and in vivo imaging has also facilitated the identification of key roles for β-catenin/integrin signaling in re-epithelialization of full-thickness skin wounds in adult zebrafish (Richardson et al, 2016). …”

“…Zebrafish will close full thickness wounds at a rate of 250 μm/hour, and frogs and salamanders will have re-epithelialized these wounds within 24 h (Levesque et al, 2010; Richardson and Hammerschmidt, 2016; Richardson et al, 2016; Seifert et al, 2012b). Each of these studies also show that the re-epithelialization process relies on migration of the keratinocytes at the leading edge of the wound, and the original wound epithelium is only 1–2 cells thick.…”