The prevalence of hearing loss after damage to the mammalian cochlea has been thought to be due to a lack of spontaneous regeneration of hair cells, the primary receptor cells for sound. Here, we show that supporting cells, which surround hair cells in the normal cochlear epithelium, differentiate into new hair cells in the neonatal mouse following ototoxic damage. Using lineage tracing, we show that new hair cells, predominantly outer hair cells, arise from Lgr5-expressing inner pillar and third Deiters cells and that new hair cell generation is increased by pharmacological inhibition of Notch. These data suggest that the neonatal mammalian cochlea has some capacity for hair cell regeneration following damage alone and that Lgr5-positive cells act as hair cell progenitors in the cochlea.

Little is known on the embryonic origin and related heterogeneity of adult neural stem cells (aNSCs). We use conditional genetic tracing, activated in a global or mosaic fashion by cell type-specific promoters or focal laser uncaging, coupled with gene expression analyses and Notch invalidations, to address this issue in the zebrafish adult telencephalon. We report that the germinal zone of the adult pallium originates from two distinct subtypes of embryonic progenitors and integrates two modes of aNSC formation. Dorsomedial aNSCs derive from the amplification of actively neurogenic radial glia of the embryonic telencephalon. On the contrary, the lateral aNSC population is formed by stepwise addition at the pallial edge from a discrete neuroepithelial progenitor pool of the posterior telencephalic roof, activated at postembryonic stages and persisting lifelong. This dual origin of the pallial germinal zone allows the temporally organized building of pallial territories as a patchwork of juxtaposed compartments.

Hearing loss due to damage to auditory hair cells is normally irreversible because mammalian hair cells do not regenerate. Here, we show that new hair cells can be induced and can cause partial recovery of hearing in ears damaged by noise trauma, when Notch signaling is inhibited by a γ-secretase inhibitor selected for potency in stimulating hair cell differentiation from inner ear stem cells in vitro. Hair cell generation resulted from an increase in the level of bHLH transcription factor Atoh1 in response to inhibition of Notch signaling. In vivo prospective labeling of Sox2-expressing cells with a Cre-lox system unambiguously demonstrated that hair cell generation resulted from transdifferentiation of supporting cells. Manipulating cell fate of cochlear sensory cells in vivo by pharmacological inhibition of Notch signaling is thus a potential therapeutic approach to the treatment of deafness.

Adult stem-cell therapy holds promise for the treatment of gastrointestinal diseases. Here we describe methods for long-term expansion of colonic stem cells positive for leucine-rich repeat containing G protein-coupled receptor 5 (Lgr5(+) cells) in culture. To test the transplantability of these cells, we reintroduced cultured GFP(+) colon organoids into superficially damaged mouse colon. The transplanted donor cells readily integrated into the mouse colon, covering the area that lacked epithelium as a result of the introduced damage in recipient mice. At 4 weeks after transplantation, the donor-derived cells constituted a single-layered epithelium, which formed self-renewing crypts that were functionally and histologically normal. Moreover, we observed long-term (textgreater6 months) engraftment with transplantation of organoids derived from a single Lgr5(+) colon stem cell after extensive in vitro expansion. These data show the feasibility of colon stem-cell therapy based on the in vitro expansion of a single adult colonic stem cell.

BACKGROUND MicroRNAs (miRs or miRNAs) regulate several biological processes in the cell. However, evidence for miRNAs that control the differentiation program of specific neural cell types has been elusive. Recently, we have shown that apoptosis-associated factors, such as p53 and caspases participate in the differentiation process of mouse neural stem (NS) cells. To identify apoptosis-associated miRNAs that might play a role in neuronal development, we performed global miRNA expression profiling experiments in NS cells. Next, we characterized the expression of proapoptotic miRNAs, including miR-16, let-7a and miR-34a in distinct models of neural differentiation, including mouse embryonic stem cells, PC12 and NT2N cells. In addition, the expression of antiapoptotic miR-19a and 20a was also evaluated. RESULTS The expression of miR-16, let-7a and miR-34a was consistently upregulated in neural differentiation models. In contrast, expression of miR-19a and miR-20a was downregulated in mouse NS cell differentiation. Importantly, differential expression of specific apoptosis-related miRNAs was not associated with increased cell death. Overexpression of miR-34a increased the proportion of postmitotic neurons of mouse NS cells. CONCLUSIONS In conclusion, the identification of miR-16, let-7a and miR-34a, whose expression patterns are conserved in mouse, rat and human neural differentiation, implicates these specific miRNAs in mammalian neuronal development. The results provide new insights into the regulation of neuronal differentiation by apoptosis-associated miRNAs.