Circadian rhythms are a pervasive property of mammalian cells, tissues and behaviour, ensuring physiological adaptation to solar time. Models of cellular timekeeping revolve around transcriptional feedback repression, whereby CLOCK and BMAL1 activate the expression of PERIOD (PER) and CRYPTOCHROME (CRY), which in turn repress CLOCK/BMAL1 activity. CRY proteins are therefore considered essential components of the cellular clock mechanism, supported by behavioural arrhythmicity of CRY-deficient (CKO) mice under constant conditions. Challenging this interpretation, we find locomotor rhythms in adult CKO mice under specific environmental conditions and circadian rhythms in cellular PER2 levels when CRY is absent. CRY-less oscillations are variable in their expression and have shorter periods than wild-type controls. Importantly, we find classic circadian hallmarks such as temperature compensation and period determination by CK1δ/ϵ activity to be maintained. In the absence of CRY-mediated feedback repression and rhythmic Per2 transcription, PER2 protein rhythms are sustained for several cycles, accompanied by circadian variation in protein stability. We suggest that, whereas circadian transcriptional feedback imparts robustness and functionality onto biological clocks, the core timekeeping mechanism is post-translational.

Recessive dystrophic epidermolysis bullosa (RDEB) is a complex inherited skin disorder caused by loss-of-function mutations in the COL7A1 gene. In order for an effective treatment of this disorder to be realized, both a thorough understanding of the regulation of COL7A1 and an understanding of the underlying nature of the complications of RDEB is needed. Currently, both post-transcriptional regulation of COL7A1 and the underlying causes of fibrosis in RDEB patients are poorly understood. Here, we describe a previously unknown mechanism of regulation by which miR-29 regulates COL7A1 in a complex network: both directly through targeting its 3’ UTR at two distinct seed regions and indirectly through targeting an essential transcription factor required for basal COL7A1 expression, SP1. In turn miR-29 itself is regulated by SP1 activity and TGF-β signaling. RDEB mice express high levels of TGF-β and significantly lower miR-29 when compared to wild-type cohorts. The sustained decrease in miR-29 in RDEB skin leads to an increase of miR-29 target genes expressed in the skin, including pro-fibrotic extracellular matrix collagens. Collectively, we identify miR-29 as an important factor in both regulating COL7A1 and inhibiting TGF-β mediated fibrosis.

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Epidermolysis bullosa is classified as a genodermatosis, an inherited genetic skin disorder that results in severe, chronic skin blistering with painful and life-threatening complications. Although there is currently no cure for epidermolysis bullosa, concurrent advances in gene and stem cell therapies are converging toward combinatorial therapies that hold the promise of clinically meaningful and lifelong improvement. Recent studies using hematopoietic stem cells and mesenchymal stromal/stem cells to treat epidermolysis bullosa have demonstrated the potential for sustained, effective management of the most severe cases. Furthermore, advances in the use of gene therapy and gene-editing techniques, coupled with the development of induced pluripotent stem cells from patients with epidermolysis bullosa, allow for autologous therapies derived from a renewable population of cells that are patient-specific. Here we describe emerging treatments for epidermolysis bullosa and other genodermatoses, along with a discussion of their benefits and limitations as effective therapies.

Epidermolysis bullosa is a group of inherited disorders that can be both systemic and life-threatening. Standard treatments for the most severe forms of this disorder, typically limited to palliative care, are ineffective in reducing the morbidity and mortality due to complications of the disease. Emerging therapies—such as the use of allogeneic cellular therapy, gene therapy, and protein therapy—have all shown promise, but it is likely that several approaches will need to be combined to realize a cure. For recessive dystrophic epidermolysis bullosa, each particular therapeutic approach has added to our understanding of type VII collagen (C7) function and the basic biology surrounding the disease. The efficacy of these therapies and the mechanisms by which they function also give us insight into developing future strategies for treating this and other extracellular matrix disorders.