Interaction between transcription factors PAX6/PAX6-5a and specific members of miR-183-96-182 cluster, may contribute to glioma progression in glioblastoma cell lines.

A misbalance between proliferation and differentiation of neural stem cells in niches for adult brain neurogenesis is a key mechanism in glioma pathogenesis. In the adult brain, the expression of Pax6 marks stem cells in the forebrain neurogenic niche. We analyzed the expression profile of the two active in vertebrates Pax6 isoforms, Pax6 and Pax6-5a, along with the expression of microRNA cluster miR-183-96-182 in a large set of glioma patient specimens and glioma cell lines which showed opposite expression level, low and high, respectively, with the progression of tumor malignancy. Our results from biochemical and in vitro studies in glioma cell lines disclosed a specific regulation of the PAX6-5a isoform by miR-183. Mechanistically, we show that the downregulation of the lipid kinase SPHK1 by both PAX6 isoforms and the simultaneous induction of CTNDD2 expression, specifically by PAX6-5a, results in reduced glioma cell survival, decreased migration and invasion and increased cell death, in glioma cell lines. Taken together, our findings point towards the important role of PAX6 and define PAX6-5a as a new essential player in glioma development. Finally, we propose that the expression level of TFs PAX6/PAX6-5a and miR-183-96-182 may potentially serve as prognostic markers for the progression of glioma tumors from low- to high-grade with a potential to identify new therapeutic approaches.

Ambra1 regulates autophagy and development of the nervous system.

Autophagy is a self-degradative process involved both in basal turnover of cellular components and in response to nutrient starvation or organelle damage in a wide range of eukaryotes. During autophagy, portions of the cytoplasm are sequestered by double-membraned vesicles called autophagosomes, and are degraded after fusion with lysosomes for subsequent recycling. In vertebrates, this process acts as a pro-survival or pro-death mechanism in different physiological and pathological conditions, such as neurodegeneration and cancer; however, the roles of autophagy during embryonic development are still largely uncharacterized. Beclin1 (Becn1; coiled-coil, myosin-like BCL2-interacting protein) is a principal regulator in autophagosome formation, and its deficiency results in early embryonic lethality. Here we show that Ambra1 (activating molecule in Beclin1-regulated autophagy), a large, previously unknown protein bearing a WD40 domain at its amino terminus, regulates autophagy and has a crucial role in embryogenesis. We found that Ambra1 is a positive regulator of the Becn1-dependent programme of autophagy, as revealed by its overexpression and by RNA interference experiments in vitro. Notably, Ambra1 functional deficiency in mouse embryos leads to severe neural tube defects associated with autophagy impairment, accumulation of ubiquitinated proteins, unbalanced cell proliferation and excessive apoptotic cell death. In addition to identifying a new and essential element regulating the autophagy programme, our results provide in vivo evidence supporting the existence of a complex interplay between autophagy, cell growth and cell death required for neural development in mammals.

Conversion of cerebral cortex into basal ganglia in Emx2(-/-) Pax6(Sey/Sey) double-mutant mice.

The molecular mechanisms that activate morphogenesis of cerebral cortex are currently the subject of intensive experimental analysis. Transcription factor genes of the homeobox, basic helix-loop-helix (bHLH) and zinc-finger families have recently been shown to have essential roles in this process. However, the actual selector genes activating corticogenesis have not yet been identified. Here we show that high-level expression of at least one functional allele of either of the homeobox genes Emx2 or Pax6 in the dorsal telencephalon is necessary and sufficient to stably activate morphogenesis of cerebral cortex and to repress that of adjacent structures, such as striatum.

Emx2 and Pax6 control regionalization of the pre-neuronogenic cortical primordium.

It has recently been demonstrated that the transcription factor genes Emx2 and Pax6, expressed in the developing cerebral cortex along two complementary tangential gradients, are essential for the shaping of the cortical areal profile at late developmental ages, when cortical neuronogenesis is almost completed. In this study we addressed the question of whether cortical regionalization is already affected in Emx2 and Pax6 loss of function mutants at the beginning of neuronogenesis. By comparing expression patterns of selected molecular markers in these mutants at this age, we found that: (i) Emx2 and Pax6 are necessary for the establishment of their own specific expression profiles and are able to down-regulate each other; and (ii) absence of functional EMX2 or PAX6 proteins results in reduction of caudal-medial and rostral-lateral cortical regions, respectively, as well as in impairment of the WNT signalling center at the medial-caudal edge of the cortical field, crucial for cortical growth. These results suggest that pre-neuronogenic cortical regionalization may rely on mutual interactions between these two transcription factors and that the late areal phenotype of Emx2(-/-) and Pax6(-/-) mutants may possibly arise from both misconfiguration of the cortical molecular protomap and distortion of the cortical growth profile.