Bacterial cytokinesis is accomplished by the essential ‘divisome’ machinery. The most widely conserved divisome component, FtsZ, is a tubulin homolog that polymerizes into the ‘FtsZ-ring’ (‘Z-ring’). Previous in vitro studies suggest that Z-ring contraction serves as a major constrictive force generator to limit the progression of cytokinesis. Here, we applied quantitative superresolution imaging to examine whether and how Z-ring contraction limits the rate of septum closure during cytokinesis in Escherichia coli cells. Surprisingly, septum closure rate was robust to substantial changes in all Z-ring properties proposed to be coupled to force generation: FtsZ’s GTPase activity, Z-ring density, and the timing of Z-ring assembly and disassembly. Instead, the rate was limited by the activity of an essential cell wall synthesis enzyme and further modulated by a physical divisome–chromosome coupling. These results challenge a Z-ring–centric view of bacterial cytokinesis and identify cell wall synthesis and chromosome segregation as limiting processes of cytokinesis.

Recessive dystrophic epidermolysis bullosa (RDEB) is a severe skin fragility disorder caused by mutations in the Col7a1 gene. Patients with RDEB suffer from recurrent erosions in skin and mucous membranes and have a high risk for developing cutaneous squamous cell carcinoma (cSCCs). TGFβ signaling has been associated with fibrosis and malignancy in RDEB. In this study, the activation of TGFβ signaling was demonstrated in col7a1−/− mice as early as a week after birth starting in the interdigital folds of the paws, accompanied by increased deposition of collagen fibrils and elevated dermal expression of matrix metalloproteinase (MMP)‐9 and MMP‐13. Furthermore, human cord blood‐derived unrestricted somatic stem cells (USSCs) that we previously demonstrated to significantly improve wound healing and prolong the survival of col7a1−/− mice showed the ability to suppress TGFβ signaling and MMP‐9 and MMP‐13 expression meanwhile upregulating anti‐fibrotic TGFβ3 and decorin. In parallel, we cocultured USSCs in a transwell with RDEB patient‐derived fibroblasts, keratinocytes, and cSCC, respectively. The patient‐derived cells were constitutively active for STAT, but not TGFβ signaling. Moreover, the levels of MMP‐9 and MMP‐13 were significantly elevated in the patient derived‐keratinocytes and cSCCs. Although USSC coculture did not inhibit STAT signaling, it significantly suppressed the secretion of MMP‐9 and MMP‐13, and interferon (IFN)‐γ from RDEB patient‐derived cells. Since epithelial expression of these MMPs is a biomarker of malignant transformation and correlates with the degree of tumor invasion, these results suggest a potential role for USSCs in mitigating epithelial malignancy, in addition to their anti‐inflammatory and anti‐fibrotic functions. Stem Cells 2018;36:1839–12

Recessive dystrophic epidermolysis bullosa (RDEB) is a devastating inherited skin blistering disease caused by mutations in the COL7A1 gene that encodes type VII collagen (C7), a major structural component of anchoring fibrils at the dermal‐epidermal junction (DEJ). We recently demonstrated that human cord blood‐derived unrestricted somatic stem cells promote wound healing and ameliorate the blistering phenotype in a RDEB (col7a1 −/−) mouse model. Here, we demonstrate significant therapeutic effect of a further novel stem cell product in RDEB, that is, human placental‐derived stem cells (HPDSCs), currently being used as human leukocyte antigen‐independent donor cells with allogeneic umbilical cord blood stem cell transplantation in patients with malignant and nonmalignant diseases. HPDSCs are isolated from full‐term placentas following saline perfusion, red blood cell depletion, and volume reduction. HPDSCs contain significantly higher level of both hematopoietic and nonhematopoietic stem and progenitor cells than cord blood and are low in T cell content. A single intrahepatic administration of HPDSCs significantly elongated the median life span of the col7a1 −/− mice from 2 to 7 days and an additional intrahepatic administration significantly extended the median life span to 18 days. We further demonstrated that after intrahepatic administration, HPDSCs engrafted short‐term in the organs affected by RDEB, that is, skin and gastrointestinal tract of col7a1 −/− mice, increased adhesion at the DEJ and deposited C7 even at 4 months after administration of HPDSCs, without inducing anti‐C7 antibodies. This study warrants future clinical investigation to determine the safety and efficacy of HPDSCs in patients with severe RDEB. stem cells translational medicine 2018;7:530–542

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