A New Model System for Adult Neurogenesis

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PROJECT SUMMARY In development and homeostasis, progenitor stem cells of critical organ systems often divide asymmetrically. Memory formation involves adult neurogenesis, wherein progenitor stem cells in the adult brain divide asymmetrically to produce nascent neurons. The ability to form and recall specific memories is indispensable to our survival. Patients with neurodegenerative diseases such as Alzheimer’s exhibit drastic disruptions in learning and memory. As such, elucidating the developmental and mechanistic underpinnings of memory formation is critical to identifying and preventing processes that lead to brain disease. Our long-term objective is to understand the molecular mechanisms that generate new neurons in adult brains. We have established a new model organism for tackling this problem, one that combines the neural complexity of a mammal with the ease of laboratory culture and genetic manipulation of an insect: the cricket Gryllus bimaculatus. In the cricket brain, neuroblasts are neural stem cells necessary for learning and memory. We have discovered that the conserved transcription factor CREB, which plays a central role in animal learning and memory, regulates the molecular organizer oskar, and that both genes are required for long term memory. We hypothesize that Oskar and CREB direct proper asymmetric division of neuroblasts into neurons, which allows long term memories to be established. We will test this hypothesis through pursuit of three complementary Specific Aims. In Aim 1, we will determine whether oskar regulates adult neuroblast asymmetric cell division. We will use CRISPR/Cas9 and RNAi to abrogate oskar expression and determine how this affects asymmetric cell division using in situ hybridization, immunohistochemistry, and confocal microscopy. In Aim 2, we will identify the interacting partners of Oskar within Gryllus neuroblasts. To this end, we will assess the neural expression and long-term memory function of genes known to interact with oskar in other cell types. We will also take an unbiased approach to identifying relevant oskar interactors by using single cell RNA-seq to determine the complete transcriptome of neuroblasts. In Aim 3, we will define the role of CREB in regulating neuroblast division. We will reduce CREB expression in the adult brain and examine how CREB loss affects neuroblast asymmetric cell division. The results of these experiments will shed light on the cellular mechanisms that regulate memory formation, which could lead to novel approaches to ameliorate memory-related diseases.