changes in the cytoskeleton, e.g., membrane protrusion and generation of new sites of substrate adhesion at the front, as well as actin disassembly and cell detachment at the rear. Small GTPases and protein kinases play essential roles in actin dynamics and cell migration processes, and closure of scratch wounds Figure 1. Expression of HGF/SF and c-Met during wound healing. (A) Scheme of a wound section 3–5 d after injury. Keratinocytes (red) at the wound edge proliferate and migrate down the injured dermis to form the so-called HE (arrow). D, dermis; Es, eschar; F, fatty tissue; G, granulation tis- sue. (B and C) In situ hybridization of wounded skin with a HGF/SF probe 1 (B) and 3 d (C) after injury. Note that HGF/SF at day 1 is expressed in the hair follicles and around the clot, which is where inﬂammatory cells ac- cumulate and inﬁltrate the wound. 3 d after wounding, HGF/SF is highly expressed in the HE. (E and F) In situ hybridization with the c-Met probe 1 (D) and 3 d (E) after injury. Note that c-Met is expressed in the epidermis, in hair follicles, and in the HE 3 d after wounding. (D and G) In situ hybridi- zation with sense probes of HGF/SF (F) and c-Met (G). Bar, 50 μm. 152 JCB • VOLUME 177 • NUMBER 1 • 2007 in cultured cells depends on Rho and Rac as well as c-Jun N-terminal kinase (Ridley et al., 1995; Fenteany et al., 2000; Lamorte et al., 2000; Raftopoulou and Hall, 2004). Wound closure in vitro is not only achieved by activities restricted to cells in the front row, but also involves cells further away from the wound edge (Farooqui and Fenteany, 2005). Thus, disper- sion and migration of single cells at the wound edge is observed, which is accompanied by movement of back row cells that maintain their cell–cell contacts and migrate as coherent cell sheets. The cellular and molecular mechanisms during the clo- sure of scratch wounds in vitro resemble those involved in the migration of epithelial cells during the healing of skin wounds. Hepatocyte growth factor/scatter factor (HGF/SF) and its receptor c-Met promote proliferation of epithelial cells in cul- ture, and can dissociate and scatter MDCK cells, which is ac- companied by an increase in their motility (Stoker et al., 1987; Miyazawa et al., 1989; Weidner et al., 1991; Nakamura et al., 1989; Bottaro et al., 1991; for review see Birchmeier et al., 2003). Mutation of the HGF/SF and c-Met genes in mice dem- onstrated that this signaling system is important during verte- brate embryogenesis (Bladt et al., 1995; Schmidt et al., 1995; Uehara et al., 1995). During development, HGF/SF and c-Met control cell survival and proliferation of hepatocytes, as well as the formation of the placenta. Furthermore, HGF/SF and c-Met are essential regulators of cell motility. HGF/SF signals release cells from dermomyotome, and they subsequently migrate to targets where they form skeletal muscle (Bladt et al., 1995; Birchmeier and Gherardi, 1998; Dietrich et al., 1999). HGF/SF and c-Met have also been implicated in various physiological and pathophysiological processes in the adult. For instance, during liver regeneration, HGF/SF levels in the blood stream raise, and conditional mutagenesis in mice has shown that the c-Met receptor is essential during liver regeneration and repair (Michalopoulos and DeFrances, 1997; Borowiak et al., 2004; Huh et al., 2004; Taub, 2004). Furthermore, up-regulated HGF/ SF and c-Met expression was observed after injury of other tis- sues, for instance the lung, kidney, heart, and skin (Kawaida et al., 1994; Ohmichi et al., 1996; Nakamura et al., 2000; Cowin et al., 2001; Yoshida et al., 2003). Thus, up-regulated HGF/SF and c-Met expression might be part of a general response to tissue damage, and it is interesting to note that cytokines such as inter- leukin 1 or 6 activate HGF/SF transcription (Michalopoulos and DeFrances, 1997). Moreover, application of exogenous HGF/SF to skin wounds promotes the formation of granulation tissue, angiogenesis, and reepithelialization, whereas neutralization of HGF/SF by the application of antibodies delays these processes (Toyoda et al., 2001; Yoshida et al., 2003; Bevan et al., 2004). We report that both HGF/SF and c-Met are up-regulated in the HE during wound repair in mice, suggesting that HGF/SF and c-Met signal may act in an autocrine manner to promote wound healing. We generated conditional mutant mice, in which c-Met was inactivated in the epidermis by the use of a keratin 14 (K14) promoter-driven cre recombinase. This resulted in the mutation of c-Met in 95% of the epidermal cells. The HE of wounds was collected by laser capture microdissection from mutant and control mice, and Southern blotting was performed to analyze the contribution of c-Met mutant keratinocytes to the