A Novel Mutation in Brain Tumor Causes Both Neural Over-Proliferation and Neurodegeneration in Adult Drosophila

Early Mitochondrial Fragmentation and Dysfunction in a Drosophila Model for Alzheimer's Disease

Many different cellular systems and molecular processes become compromised in Alzheimer's disease (AD) including proteostasis, autophagy, inflammatory responses, synapse and neuronal circuitry, and mitochondrial function. We focused in this study on mitochondrial dysfunction owing to the toxic neuronal environment produced by expression of Aβ42, and its relationship to other pathologies found in AD including increased neuronal apoptosis, plaque deposition, and memory impairment. Using super-resolution microscopy, we have assayed mitochondrial status in the three distinct neuronal compartments (somatic, dendritic, axonal) of mushroom body neurons of Drosophila expressing Aβ42. The mushroom body neurons comprise a major center for olfactory memory formation in insects. We employed calcium imaging to measure mitochondrial function, immunohistochemical and staining techniques to measure apoptosis and plaque formation, and olfactory classical conditioning to measure learning. We found that mitochondria become fragmented at a very early age along with decreased function measured by mitochondrial calcium entry. Increased apoptosis and plaque deposition also occur early, yet interestingly, a learning impairment was found only after a much longer period of time-10 days, which is a large fraction of the fly's lifespan. This is similar to the pronounced delay between cellular pathologies and the emergence of a memory dysfunction in humans. Our studies are consistent with the model that mitochondrial dysfunction and/or other cellular pathologies emerge at an early age and lead to much later learning impairments. The results obtained further develop this Drosophila model as a useful in vivo system for probing the mechanisms by which Aβ42 produces mitochondrial and other cellular toxicities that produce memory dysfunction.

Modeling Neurodegenerative Disorders in Drosophila melanogaster

Drosophila melanogaster provides a powerful genetic model system in which to investigate the molecular mechanisms underlying neurodegenerative diseases. In this review, we discuss recent progress in Drosophila modeling Alzheimer's Disease, Parkinson's Disease, Amyotrophic Lateral Sclerosis (ALS), Huntington's Disease, Ataxia Telangiectasia, and neurodegeneration related to mitochondrial dysfunction or traumatic brain injury. We close by discussing recent progress using Drosophila models of neural regeneration and how these are likely to provide critical insights into future treatments for neurodegenerative disorders.

The Role of Dynamic miRISC During Neuronal Development

Activity-dependent protein synthesis plays an important role during neuronal development by fine-tuning the formation and function of neuronal circuits. Recent studies have shown that miRNAs are integral to this regulation because of their ability to control protein synthesis in a rapid, specific and potentially reversible manner. miRNA mediated regulation is a multistep process that involves inhibition of translation before degradation of targeted mRNA, which provides the possibility to store and reverse the inhibition at multiple stages. This flexibility is primarily thought to be derived from the composition of miRNA induced silencing complex (miRISC). AGO2 is likely the only obligatory component of miRISC, while multiple RBPs are shown to be associated with this core miRISC to form diverse miRISC complexes. The formation of these heterogeneous miRISC complexes is intricately regulated by various extracellular signals and cell-specific contexts. In this review, we discuss the composition of miRISC and its functions during neuronal development. Neurodevelopment is guided by both internal programs and external cues. Neuronal activity and external signals play an important role in the formation and refining of the neuronal network. miRISC composition and diversity have a critical role at distinct stages of neurodevelopment. Even though there is a good amount of literature available on the role of miRNAs mediated regulation of neuronal development, surprisingly the role of miRISC composition and its functional dynamics in neuronal development is not much discussed. In this article, we review the available literature on the heterogeneity of the neuronal miRISC composition and how this may influence translation regulation in the context of neuronal development.

Neural stem cell dynamics: the development of brain tumours

Determining the premalignant lesions that develop into malignant tumours remains a daunting task. Brain tumours are frequently characterised by a block in differentiation, implying that normal developmental pathways become hijacked during tumourigenesis. However, the heterogeneity of stem cells and their progenitors in the brain suggests there are many potential routes to tumour initiation. Studies in Drosophila melanogaster have enhanced our understanding of the tumourigenic potential of distinct cell types in the brain. Here we review recent studies that have improved our knowledge of neural stem cell behaviour during development and in brain tumour models.