Mesenchymal stem cells (MSCs) can differentiate not only into mesenchymal lineage cells but also into various other cell lineages. As MSCs can easily be isolated from bone marrow, they can be used in various tissue engineering strategies. In this study, we assessed whether MSCs can differentiate into multiple skin cell types including keratinocytes and contribute to wound repair. First, we found keratin 14-positive cells, presumed to be keratinocytes that transdifferentiated from MSCs in vitro. Next, we assessed whether MSCs can transdifferentiate into multiple skin cell types in vivo. At sites of mouse wounds that had been i.v. injected with MSCs derived from GFP transgenic mice, we detected GFP-positive cells associated with specific markers for keratinocytes, endothelial cells, and pericytes. Because MSCs are predominantly located in bone marrow, we investigated the main MSC recruitment mechanism. MSCs expressed several chemokine receptors; especially CCR7, which is a receptor of SLC/CCL21, that enhanced MSC migration. Finally, MSC-injected mice underwent rapid wound repaired. Furthermore, intradermal injection of SLC/CCL21 increased the migration of MSCs, which resulted in an even greater acceleration of wound repair. Taken together, we have demonstrated that MSCs contribute to wound repair via processes involving MSCs differentiation various cell components of the skin.

We have made a detailed study of the X-chromosome replication pattern during the period when X-inactivation is occurring in the mouse embryo. Our observations show unequivocal regionalization of the embryo with respect to the temporal X-chromosome. The switch from isocyclic to allocyclic replication occurs in the embryonic ectoderm at approximately 6 days of development and is random with respect to parental origin of the X-chromosome. In the extra-embryonic tissues, however, the switch to allocyclic replication has apparently occurred prior to 5.3 days of development and almost exclusively involves the paternally-derived X-chromosome. Since these findings are consistent with results obtained in biochemical studies of X-chromosome activity in female embryos, we conclude that there is a close temporal relationship between the cytogenetic and biochemical manifestations of the X-inactivation process. In addition, we have observed a pattern of early paternal X-chromosome replication, transitory in some cases, that is unique to extra-embryonic tissues. These results suggest that there may be some differences in the mechanism by which X-inactivation occurs in the extra-embryonic tissues as compared with the embryonic ectoderm.

We isolated a membrane-bound metallopeptidase, DINE (damageinduced neuronal endopeptidase), by differential display PCR using rat normal and axotomized hypoglossal nuclei. The most marked properties of DINE were neuron-specific expression and a striking response to axonal injury in both the central nervous system and peripheral nervous system. For instance, cranial and spinal nerve transection, ischemia, corpus callosum transection, and colchicine treatment increased DINE mRNA expression in the injured neurons, whereas kainate-induced hyperexcitation, immobilization, and osmotic stress failed to up-regulate DINE mRNA. Expression of DINE in COS cells partially inhibited C2-ceramide-induced apoptosis, probably because of the activation of antioxidant enzymes such as Cu͞Zn-superoxide dismutase, Mn-superoxide dismutase, and glutathione peroxidase through the proteolytic activity of DINE. These data provide insight into the mechanism of how injured neurons protect themselves against neuronal death. P eripheral nerve regeneration entails sequential changes in the expression of thousands of genes, which are necessary to protect damaged neurons from death, activate surrounding glial cells, and accelerate neurite elongation. For the last few years, we have attempted to identify molecules involved in this process by using a technique known as differential display PCR (DD-PCR) and random cloning with a specific cDNA library derived from nerve-injured hypoglossal nuclei (1, 2).Among the molecules we have identified as being markedly up-regulated in response to nerve injury (3, 4), growth factors, cytokines, and neuropeptides are well established as survival factors for injured neurons (5). These molecules might participate in the protective process as intercellular signaling molecules via secretion in an autocrine or paracrine manner. Generally, secreted proteins such as neuropeptides and growth factors are biosynthesized as large precursor proteins, and processing occurs in the trans-Golgi network by endoproteolytic serine proteases, which are members of the proprotein convertase (PC) family (6). An increasing number of other secreted proteins now are recognized as being derived from integral plasma membrane proteins by hydrolysis (shedding) on the cell surface (7). Proteins secreted in this fashion include some membrane receptors, receptor ligands, ectoenzymes, and cell adhesion molecules. These ectodomain shedding events have been shown to be associated with metalloprotease inhibitors (8). Since identification of the ADAM (a disintegrin and metalloproteinase) family (9) and MMP (matrix metalloprotease) family, our understanding of the shedding events on the cell surface has greatly improved in recent years.As for nerve regeneration, the repertoire of proteases involved in the process is limited. Among regeneration processes, the roles of proteases in a process of axon elongation are relatively well studied both in vitro and in vivo. It has been assumed that this axonal behavior is, for instance, a consequence of the bala...

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