RNAi of Ast1 and CHF: A Molecular Approach to Exploring the Connection between the Innate Immune System and Adult Neurogenesis in Procambarid Crayfish

Adult neurogenesis, the process by which new neurons are born and integrate into distinct regions of the adult brain, occurs across a phylogenetically vast array of species. In mammals, new neurons arise from self-renewing neural stem cells housed in neurogenic niches, but the neural precursors in the freshwater crayfish Procambarus clarkii do not undergo these self-renewing divisions. Despite the persistence of neurogenesis throughout their relatively long (~20 year) lives, these organisms never experience a depletion of neurogenic niche cells; their neural precursor cells therefore must be provided by a source extrinsic to the brain. Immune tissue-produced semi-granular hemocyte cells exhibit a strong affinity for the neurogenic niche in vitro and in vivo, and their descendants integrate into the brain and express neural properties, implicating these cells as the primary neural precursors in P. clarkii. The proliferation and release of semi-granular hemocytes from the immune tissues are largely regulated by two proteins: astakine 1 (Ast1), which promotes hemocyte differentiation along the semi-granular lineage, and crustacean hematopoietic factor (CHF), an anti-apoptotic agent. Because these proteins potently regulate proliferation of the semi-granular hemocyte neural precursors, they are also likely to modulate neurogenic rates. We aim to deduce the involvement of these proteins in adult neurogenesis by reducing their expression levels using RNA interference (RNAi), and assessing resulting changes to neurogenic rate. To this end, the double stranded RNAs (dsRNAs) necessary to reduce Ast1 and CHF expression knockdown have been synthesized and purified. To confirm that these dsRNAs would successfully suppress Ast1 and CHF expression in P. clarkii cells, initial RNAi experiments were attempted in vitro. Although no clear evidence of successful expression knockdown was obtained from these experiments, they have led to the refinement of our RNAi protocol. Through further refinements to this protocol, we will be able to confirm the effects of RNAi on Ast1 and CHF expression. With this confirmation, we will transition to performing RNAi in vivo, where the impacts of Ast1 and CHF expression on neurogenesis can be directly monitored