Drosophila neuroblasts are a model system for studying asymmetric cell division: they divide unequally to produce an apical neuroblast and a basal ganglion mother cell that differ in size, mitotic activity and developmental potential. During neuroblast mitosis, an apical protein complex orients the mitotic spindle and targets determinants of cell fate to the basal cortex, but the mechanism of each process is unknown. Here we show that the tumour-suppressor genes lethal giant larvae (lgl) and discs large (dlg) regulate basal protein targeting, but not apical complex formation or spindle orientation, in both embryonic and larval neuroblasts. Dlg protein is apically enriched and is required for maintaining cortical localization of Lgl protein. Basal protein targeting requires microfilament and myosin function, yet the lgl phenotype is strongly suppressed by reducing levels of myosin II. We conclude that Dlg and Lgl promote, and myosin II inhibits, actomyosin-dependent basal protein targeting in neuroblasts.

New neurons are added to the adult hippocampus throughout life and contribute to cognitive functions including learning and memory. It remains unclear whether ongoing neurogenesis arises from self-renewing neural stem cells (NSC) or from multipotential progenitor cells that cannot self-renew in the hippocampus. This is largely based on observations that neural precursors derived from the subventricular zone (SVZ) can be passaged long-term whereas hippocampal subgranular zone (SGZ) precursors are rapidly depleted by passaging. We demonstrate here that high levels of BMP signaling occur in hippocampal but not SVZ precursors in vitro, and blocking BMP signaling with Noggin is sufficient to foster hippocampal cell self-renewal, proliferation, and multipotentiality using single cell clonal analysis. Moreover, NSC maintenance requires continual Noggin exposure, which implicates BMPs as crucial requlators of NSC aging. In vivo, Noggin is expressed in the adult dentate gyrus and limits BMP signaling in proliferative cells of the SGZ. Transgenic Noggin overexpression in the SGZ increases multiple precursor cell populations, but proportionally increases the glial fibrillary acidic protein (GFAP)+ cell population at the expense of other precursors, suggesting that Noggin acts on NSCs in vivo. To confirm this, we used a dual thymidine analog paradigm to repeatedly label slowly dividing cells over a long duration. We find that small populations of label-retaining cells exist in the SGZ and that Noggin overexpression increases their numbers. Thus, we propose that the adult hippocampus contains a population of NSCs, which can be expanded both in vitro and in vivo by blocking BMP signaling.

The ventral spinal cord generates multiple inhibitory and excitatory interneuron subtypes from four cardinal progenitor domains (p0, p1, p2, p3). Here we show that cell-cell interactions mediated by the Notch receptor play a critical evolutionarily conserved role in the generation of excitatory v2aIN and inhibitory v2bIN interneurons. Lineage-tracing experiments show that the v2aIN and v2bIN develop from genetically identical p2 progenitors. The p2 daughter cell fate is controlled by Delta4 activation of Notch receptors together with MAML factors. Cells receiving Notch signals activate a transcription factor code that specifies the v2bIN fate, whereas cells deprived of Notch signaling express another code for v2aIN formation. Thus, our study provides insight into the cell-extrinsic signaling that controls combinatorial transcription factor profiles involved in regulating the process of interneuron subtype diversification.

The ventral spinal cord consists of interneuron groups arising from distinct, genetically defined, progenitor domains along the dorsoventral axis. Many of these interneuron groups settle in the ventral spinal cord which, in mammals, contains the central pattern generator for locomotion. In order to better understand the locomotor networks, we have used different transgenic mice for anatomical characterization of one of these interneuron groups, called V2 interneurons. Neurons in this group are either V2a interneurons marked by the postmitotic expression of the transcription factor Chx10, or V2b interneurons which express the transcription factors Gata2 and Gata3. We found that all V2a and most V2b interneurons were ipsilaterally projecting in embryos as well as in newborns. V2a interneurons were for the most part glutamatergic while V2b interneurons were mainly GABAergic or glycinergic. Furthermore, we demonstrated that a large proportion of V2 interneurons expressed the axon guidance molecule EphA4, a molecule previously shown to be important for correct organization of locomotor networks. We also showed that V2 interneurons and motor neurons alone did not account for all EphA4-expressing neurons in the spinal cord. Together, these findings enable a better interpretation of neural networks underlying locomotion, and open up the search for as yet unknown components of the mammalian central pattern generator.

Glioblastoma multiforme (GBM) is a lethal, therapy-resistant brain cancer consisting of numerous tumor cell subpopulations, including stem-like glioma-initiating cells (GICs), which contribute to tumor recurrence following initial response to therapy. Here, we identified miR-182 as a regulator of apoptosis, growth, and differentiation programs whose expression level is correlated with GBM patient survival. Repression of Bcl2-like12 (Bcl2L12), cMet, and hypoxia-inducible factor 2α (HIF2A) is of central importance to miR-182 anti-tumor activity, as it results in enhanced therapy susceptibility, decreased GIC sphere size, expansion, and stemness in vitro. To evaluate the tumor-suppressive function of miR-182 in vivo, we synthesized miR-182-based spherical nucleic acids (182-SNAs); i.e., gold nanoparticles covalently functionalized with mature miR-182 duplexes. Intravenously administered 182-SNAs penetrated the blood-brain/blood-tumor barriers (BBB/BTB) in orthotopic GBM xenografts and selectively disseminated throughout extravascular glioma parenchyma, causing reduced tumor burden and increased animal survival. Our results indicate that harnessing the anti-tumor activities of miR-182 via safe and robust delivery of 182-SNAs represents a novel strategy for therapeutic intervention in GBM.

The etiology of major depressive disorder (MDD), the leading cause of worldwide disability, is unknown. The neurogenic hypothesis proposes that MDD is linked to impairments of adult neurogenesis in the hippocampal dentate gyrus (DG), while the effects of antidepressants are mediated by increased neurogenesis. However, alterations in neurogenesis and endophenotypes are not always causally linked, and the relationship between increased neurogenesis and altered behavior is controversial. To address causality, we used chemogenetics in transgenic mice to selectively manipulate activity of newborn DG neurons. Suppressing excitability of newborn neurons without altering neurogenesis abolish the antidepressant effects of fluoxetine. Remarkably, activating these neurons is sufficient to alleviate depression-like behavior and reverse the adverse effects of unpredictable chronic mild stress. Our results demonstrate a direct causal relationship between newborn neuronal activity and affective behavior. Thus, strategies that target not only neurogenesis but also activity of newborn neurons may lead to more effective antidepressants.

Heterotopic ossification (HO), acquired or hereditary, is the formation of true bone outside of the normal skeleton. Although the lineages of cells contributing to bone formation during normal development are well defined, the precise lineages of cells that contribute to HO are not clear. This study utilized Cre-lox based genetic lineage tracing to examine the contribution to HO of cells that expressed either FoxD1 or Glast. Both lineages contributed broadly to different normal tissues, and FoxD1-cre labeled cells contributed to normal bone formation. Despite the similarity in labeling patterns of normal tissues, and the significant contribution of FoxD1-cre labeled cells to normal bone, only Glast-creERT labeled progenitors contributed significantly to HO at all stages, suggesting the cell populations that normally contribute to physiological bone formation, such as the Foxd1-cre labeled cells, may not participate in pathological HO. Further, identification of Glast-expressing cells as precursors that give rise to HO should help with molecular targeting of this population both for the prevention and for the treatment of HO.

Fibrodysplasia ossificans progressiva (FOP) is a rare genetic disorder of progressive heterotopic ossification (HO) caused by a recurrent activating mutation of ACVR1/ALK2, a bone morphogenetic protein (BMP) type I receptor. FOP is characterized by progressive HO, which is associated with inflammation in the setting of dysregulated BMP signaling, however, a variety of atypical neurologic symptoms are also reported by FOP patients. The main objective of this study is to investigate the potential underlying mechanism that is responsible for the observed atypical neurologic symptoms. We evaluated two mouse models of dysregulated BMP signaling for potential CNS pathology through noninvasive magnetic resonance imaging (MRI) studies and histological and immunohistochemical approaches. In one model, BMP4 is over-expressed under the control of the neuron-specific enolase promoter; the second model is a knock-in of a recurrent FOP mutation of ACVR1/ALK2. We also retrospectively examined MRI scans of four FOP patients. We consistently observed demyelinated lesions and focal inflammatory changes of the CNS in both mouse models but not in wild-type controls, and also found CNS white matter lesions in each of the four FOP patients examined. These findings suggest that dysregulated BMP signaling disturbs normal homeostasis of target tissues, including CNS where focal demyelination may manifest as the neurologic symptoms frequently observed in FOP.