The epidermis, the outer layer of the skin composed of keratinocytes, is a stratified epithelium that functions as a barrier to protect the organism from dehydration and external insults. The epidermis develops depending on the transcription factor p63, a member of the p53 family of transcription factors. p63 is strongly expressed in the innermost basal layer where epithelial cells with high clonogenic and proliferative capacity reside. Deletion of p63 in mice results in a dramatic loss of all keratinocytes and loss of stratified epithelia, probably due to a premature proliferative rundown of the stem and transient amplifying cells. Here we report that microRNA (miR)-203 is induced in vitro in primary keratinocytes in parallel with differentiation. We found that miR-203 specifically targets human and mouse p63 3 0 -UTRs and not SOCS-3, despite bioinformatics alignment between miR-203 and SOCS-3 3 0 -UTR. We also show that miR-203 overexpression in proliferating keratinocytes is not sufficient to induce full epidermal differentiation in vitro. In addition, we demonstrate that miR-203 is downregulated during the epithelial commitment of embryonic stem cells, and that overexpression of miR-203 in rapidly proliferating human primary keratinocytes significantly reduces their clonogenic capacity. The results suggest that miR-203, by regulating the DNp63 expression level, is a key molecule controlling the p63-dependent proliferative potential of epithelial precursor cells both during keratinocyte differentiation and in epithelial development. In addition, we have shown that miR-203 can regulate DNp63 levels upon genotoxic damage in head and neck squamous cell carcinoma cells, thus controlling cell survival.

Cell replacement therapies for neurodegenerative disease have focused on transplantation of the cell types affected by the pathological process. Here we describe an alternative strategy for Parkinson's disease in which dopamine neurons are generated by direct conversion of astrocytes. Using three transcription factors, NEUROD1, ASCL1 and LMX1A, and the microRNA miR218, collectively designated NeAL218, we reprogram human astrocytes in vitro, and mouse astrocytes in vivo, into induced dopamine neurons (iDANs). Reprogramming efficiency in vitro is improved by small molecules that promote chromatin remodeling and activate the TGFβ, Shh and Wnt signaling pathways. The reprogramming efficiency of human astrocytes reaches up to 16%, resulting in iDANs with appropriate midbrain markers and excitability. In a mouse model of Parkinson's disease, NeAL218 alone reprograms adult striatal astrocytes into iDANs that are excitable and correct some aspects of motor behavior in vivo, including gait impairments. With further optimization, this approach may enable clinical therapies for Parkinson's disease by delivery of genes rather than cells.

The p53-family member TAp73 is a transcription factor that plays a key role in many biological processes. Here, we show that p73 drives the expression of microRNA (miR)-34a, but not miR-34b and -c, by acting on specific binding sites on the miR-34a promoter. Expression of miR-34a is modulated in parallel with that of TAp73 during in vitro differentiation of neuroblastoma cells and cortical neurons. Retinoid-driven neuroblastoma differentiation is inhibited by knockdown of either p73 or miR-34a. Transcript expression of miR-34a is significantly reduced in vivo both in the cortex and hippocampus of p73 −/− mice; miR-34a and TAp73 expression also increase during postnatal development of the brain and cerebellum when synaptogenesis occurs. Accordingly, overexpression or silencing of miR-34a inversely modulates expression of synaptic targets, including synaptotagmin-1 and syntaxin-1A. Notably, the axis TAp73/miR-34a/synaptotagmin-1 is conserved in brains from Alzheimer's patients. These data reinforce a role for TAp73 in neuronal development.cell death | neurodegeneration | Alzheimer disease T he p53-family member Trp73 is transcribed from two distinct promoters, resulting in isoforms containing or lacking the Nterminal TA domain, known as TAp73 (1, 2) and ΔNp73 (3), respectively; additionally, alternative 3′-splicing produces further variants (α, β, and so forth). In keeping with their sequence and structural similarities, TAp73 can mimic several p53 functions, including the transactivation of p21, Puma, and Bax, although p73 also has distinct transcriptional targets. Indeed, p73 −/− mice show developmental defects of the CNS; for example, congenital hydrocephalus, hippocampal dysgenesis, and defects of pheromone detection rather than the enhanced tumor susceptibility of p53 −/− mice (4). This development is not simply because of apoptosis, as the ectopic expression of p73 induces neurite outgrowth and expression of neuronal markers in neuroblastoma cell lines (5) and in primary oligodendrocytes (6).Several microRNAs (miRs) are regulated by p53 (7), although p73-dependent miRs have been less well studied. In particular, the miR-34 family (miR-34a to -c) has been shown to be a direct target of p53 (8-10). Ectopic expression of miR-34 mimics several p53 effects, although in a cell type-specific manner. In mice, miR-34a is ubiquitous with the highest expression in brain, and overexpression of miR-34a in neuroblastoma cell lines modulates neuronal-specific genes (11); miR-34b and -c are mainly in the lung (12).Because both p73 and miRs, including miR-34a, have been implicated in neuronal differentiation, we have investigated the possibility that p73 drives miR-34a expression using WT and p73-null mice. We demonstrate that miR-34a is transcriptionally regulated by TAp73 and that, in turn, miR-34a regulates the expression of a number of synaptic proteins, in particular synaptotagmin I and syntaxin 1A in cortical neurons. Moreover, neuronal architecture is disorganized in p73-null mice, and manipulation of miR-34a expressi...