br Results br Discussion Our data indicated

Results
Discussion Our data indicated that phenotype-linked transcriptomics of GSCs overlapped with tumor anatomic site, with mesenchymal-like/nodular signatures prevalent in perinecrotic zones and proneural-like/invasive signature in infiltrating areas of tumor, suggesting that these GSCs both shape and adapt to microenvironmental conditions, and that complex intratumoral architecture likely arises from the co-existence of diverse GSCs within individual tumors (Patel et al., 2014). Our data strongly implicated that EV-mediated transfer of bioactive molecules leads to increased heterogeneity not due to passive transfer but via cell-specific targeting, as both cellular and EV microRNAs have a cell-specific function, targeting effectors existing exclusively in particular GSC subpopulations. EV-microRNA transfer between different subpopulations of tumor cells should be thus recognized as an important aspect of tumor intricacy that may propagate heterogeneity of GBM; thus, EV-microRNA secretion and uptake may be an additional trait of cellular Wnt agonist 1 into different anatomic niches. Recent evidence suggests that the microRNA repertoire in EVs only partially mirrors that of cellular microRNA and, in fact, its specific pattern may be surprisingly different from that of secreting cells (Koppers-Lalic et al., 2014; Skog et al., 2008). Our data strongly support the existence of an active mechanism of microRNA loading or, rather, the co-existence of diverse mechanisms, as global, non-random distribution of microRNA was detected in subclasses of GSC EVs. The complexity of solid tumors, including GBM, and their distinct pathophysiology relies on anatomic niches that transmit and receive signals through cellular and acellular mediators (Jones and Wagers, 2008). These components are highly reliant on each other and undergo constant architectural, phenotypic, and transcriptomic rearrangements depending on fluctuating microenvironmental contexts as the disease progresses. The brain tumor “ecosystem” is composed of distinct phenotypic and transcriptomic cell components, and our analysis of cellular and EV microRNA load discovered additional aspects of intratumoral diversity. EVs/microRNA as transcriptome and signaling communication tandem modulators arrange both molecular and phenotypic traits. We thus argue that observed highly heterogeneous profiles of microRNA expression in GBM and the co-existence of diverse subtypes and hybrid-stage cells within individual tumors is propagated by intratumoral exchange of microRNA.
Experimental Procedures
Author Contributions
Introduction The regenerative capacity of the mammalian CNS is largely restricted to two areas of neurogenic potential found in the subgranular zone of the dentate gyrus and the subventricular zone (SVZ) of the lateral ventricle (Kempermann et al., 2015; Ming and Song, 2011). Neurons lost outside these areas due to injury or disease cannot be replaced, and can often have devastating consequences for affected patients. Recent studies have focused on therapies involving the transdifferentiation, or direct lineage conversion, of other resident cell types into a desired neuronal population in vivo with the hopes of being able to restore or replace lost neurons (Aravantinou-Fatorou et al., 2015; Corti et al., 2012; Guo et al., 2013; Liu et al., 2015; Niu et al., 2013; Torper et al., 2013). During the acute phase of injury to the CNS, astrocytes become hypertrophic, resume proliferation, and upregulate expression of the intermediate filament proteins glial fibrillary acidic protein (GFAP) and vimentin in a process called reactive gliosis (Anderson et al., 2014; Bayraktar et al., 2015; Burda and Sofroniew, 2014). Many of the cellular processes associated with this phenomenon are transitive in nature, and are complete several weeks to a month after injury (Burda and Sofroniew, 2014; Robel et al., 2011). After injury to the CNS astrocytes become proliferative, and in some cases begin to express markers of neural stem/progenitor cells and neurogenic differentiation, indicating that they may be prime cellular candidates for transdifferentiation approaches (Anderson et al., 2014; Bayraktar et al., 2015; Duan et al., 2015; Magnusson et al., 2014; Nato et al., 2015). Recent work has demonstrated robust transdifferentiation of reactive cortical astrocytes into glutamatergic neurons with the overexpression of a single transcription factor, NEUROD1 (Guo et al., 2013). By direct injection of a retrovirus overexpressing NEUROD1 in the adult mouse cortex, these authors were able to successfully target and convert reactive astrocytes to neurons (Guo et al., 2013). However, what is not well understood from this study and others in the field is whether astrocyte-to-neuron conversion can still occur following the initial injury phase after reactive gliosis is resolved (Burda and Sofroniew, 2014; Guo et al., 2013; Niu et al., 2013; Torper et al., 2013). A better understanding of the neurogenic potential of non-reactive astrocytes is therefore necessary for the future design of therapeutics administered outside the window of reactive gliosis.