Cell identity is acquired in different brain structures according to a stereotyped timing schedule, by accommodating the proliferation of multipotent progenitor cells and the generation of distinct types of mature nerve cells at precise times. However, the molecular mechanisms coupling the identity of a specific neuron and its birth date are poorly understood. In the neural retina, only late progenitor cells that divide slowly can become bipolar neurons, by the activation ofotx2andvsx1genes. InXenopus, we found thatXotx2andXvsx1translation is inhibited in early progenitor cells that divide rapidly by a set of cell cycle-related microRNAs (miRNAs). Through expression and functional screenings, we selected 4 miRNAs—mir-129, mir-155, mir-214, and mir-222—that are highly expressed at early developmental stages in the embryonic retina and bind to the 3′ UTR ofXotx2andXvsx1mRNAs inhibiting their translation. The functional inactivation of these miRNAs in vivo releases the inhibition, supporting the generation of additional bipolar cells. We propose a model in which the proliferation rate and the age of a retinal progenitor are linked to each other and determine the progenitor fate through the activity of a set of miRNAs.

Mitochondrial dysfunctions critically affect cardiomyocyte survival during ischemia/reperfusion (I/R) injury. In this scenario p53 activates multiple signaling pathways that impair cardiac mitochondria and promote cell death. p53 is a validated target of miR-30 whose levels fall under ischemic conditions. Although triiodothyronine (T3) rescues post-ischemic mitochondrial activity and cell viability, no data are available on its role in the modulation of p53 signaling in I/R. Here we test the hypothesis that early T3 supplementation in rats inhibits the post I/R activation of p53 pro-death cascade through the maintenance of miRNA 30a expression. In our model, T3 infusion improves the recovery of post-ischemic cardiac performance. At the molecular level, the beneficial effect of T3 is associated with restored levels of miR-30a expression in the area at risk (AAR) that correspond to p53 mRNA downregulation. The concomitant decrease in p53 protein content reduces Bax expression and limits mitochondrial membrane depolarization resulting in preserved mitochondrial function and decreased apoptosis and necrosis extent in the AAR. Also in primary cardiomyocyte culture of neonatal rats, T3 prevents both miR-30a downregulation and p53 raise induced by hypoxia. The regulatory effect of T3 is greatly suppressed by miR-30a knockdown. Overall these data suggest a new mechanism of T3-mediated cardioprotection that is targeted to mitochondria and acts, at least in part, through the regulation of miR-30a/p53 axis.

Despite increasing amounts of experimental evidence depicting the involvement of non-coding RNAs in cancer, the study of BRAFV600E-regulated genes has thus far focused mainly on protein-coding ones. Here, we identify and study the microRNAs that BRAFV600E regulates through the ERK pathway. By performing small RNA sequencing on A375 melanoma cells and a vemurafenib-resistant clone that was taken as negative control, we discover miR-204 and miR-211 as the miRNAs most induced by vemurafenib. We also demonstrate that, although belonging to the same family, these two miRNAs have distinctive features. miR-204 is under the control of STAT3 and its expression is induced in amelanotic melanoma cells, where it acts as an effector of vemurafenib’s anti-motility activity by targeting AP1S2. Conversely, miR-211, a known transcriptional target of MITF, is induced in melanotic melanoma cells, where it targets EDEM1 and consequently impairs the degradation of TYROSINASE (TYR) through the ER-associated degradation (ERAD) pathway. In doing so, miR-211 serves as an effector of vemurafenib’s pro-pigmentation activity. We also show that such an increase in pigmentation in turn represents an adaptive response that needs to be overcome using appropriate inhibitors in order to increase the efficacy of vemurafenib. In summary, we unveil the distinct and context-dependent activities exerted by miR-204 family members in melanoma cells. Our work challenges the widely accepted “same miRNA family = same function” rule and provides a rationale for a novel treatment strategy for melanotic melanomas that is based on the combination of ERK pathway inhibitors with pigmentation inhibitors.

• Transformed aubergine plants constitutively expressing the Dm-AMP1 antimicrobial defensin (from Dahlia merckii) were generated and characterized. • Transgenic plants were selected on kanamycin and screened by polymerase chain reaction analysis. The expression of Dm-AMP1 in plant tissues and its release in root exudates were detected by Western blot analyses. Dm-AMP1 localization was performed by immunohistochemical experiments. • Dm-AMP1 expression ranged from 0.2% to 0.48% of total soluble proteins in primary transformants and from 0.16% to 0.66% in F₂ plants. Transformed clones showed resistance to the pathogenic fungus Botrytis cinerea, whose development on leaves was reduced by 36–100%, with respect to controls. The protein was released in root exudates of the transformed plants and was active in reducing the growth of the co-cultured pathogenic fungus Verticillium albo-atrum, whereas it did not interfere with recognition responses and symbiosis establishment by the arbuscular mycorrhizal fungus Glomus mosseae. • Dm-AMP1 transformants may represent a useful model to study the interactions between genetically modified plants and pathogenic fungi or beneficial nontarget microorganisms.

MicroRNAs (miRNAs) are short 20–22 nucleotide RNA molecules that act as negative regulators of gene expression via translational repression: they have been shown to play a role in development, proliferation, stress response, and apoptosis. The transcriptional regulator LRF (Leukemia/lymphoma Related Factor) has been shown to prevent p19ARF transcription and consequently to inhibit senescence in mouse embryonic fibroblasts (MEF). Here we report, for the first time, that LRF is post-transcriptionally regulated by miR-20a. Using a gene reporter assay, direct interaction of miR-20a with the LRF 3′UTR is demonstrated. To validate the interaction miR-20a/3′UTR LRF miR-20a was over-expressed, either by transient transfection or retroviral infection, in wild type mouse embryo fibroblasts and in LRF-null MEF derived from LRF knock-out mice. We observed LRF decrease, p19ARF increase, inhibition of cell proliferation and induction of senescence. The comparison of miR-20a activity in wt and LRF-null MEF indicates that LRF is the main mediator of the miR-20a-induced senescence and that other targets are cooperating. As LRF down-regulation/p19ARF induction is always accompanied by E2F1 down-regulation and increase of p16, we propose that all these events act in synergy to accomplish miR-20a-induced senescence in MEF. Senescence has been recently revaluated as a tumor suppressor mechanism, alternative to apoptosis; from this point of view the discovery of new physiological “senescence inducer” appears to be promising as this molecule could be used as anticancer drug.