Newborn neurons are produced in the hippocampus throughout life and may contribute to specific types of learning and memory. Presumably, this requires their functional integration into pre-existing circuits. Adult hippocampal neurogenesis decreases with age, but this decline can be lessened by physical exercise, growth factors, and certain types of environmental stimuli. We hypothesize that each stage of adult newborn hippocampal neuron maturation is associated with a characteristic transcriptional profile, that newborn neurons are uniquely responsive transcriptionally, and that integration of these cells into functional circuits fundamentally alters their patterns of gene expression. Addressing these hypotheses requires new tools to determine the transcriptional profiles of a small population of cells within the intact brain. We will use retroviruses expressing Toxoplasma gondii uracil phosphoribosyltransferase (UPRT) to label adult newborn hippocampal neurons population specifically at their birth. Only these cells will be able to incorporate the nucleotide analogue, -thiouracil (4-TU), into nascent RNA transcripts. TU-tagged RNAs will be biotinylated, purified, and analyzed by RNASeq. Studies will characterize the transcriptional profiles of adult newborn hippocampal neurons in mice at various stages of maturation and after exposure to exercise, treatment with the phosphodiesterase inhibitor, Rollipam, and activation of TrkB signaling, comparing these profiles to those of pre-existing neurons. Adult newborn neuron transcripts will be analyzed to determine whether treatments that augment neurogenesis and maturation stimulate or repress particular signaling pathways that could underlie their characteristic plasticity. Retrovirally-expressed shRNAs will be utilized to test the contributions of selected gene products to morphological and functional features of newborn neuron maturation. TU-tagging performed using wild type and NMDA receptor- deficient adult newborn hippocampal neurons will allow us to determine how the excitatory synaptic activity that occurs upon functional integration changes their transcriptional program. Changes in specific transcripts will be correlated with morphological maturation, assessed using confocal microscopy, and functional properties, determined electrophysiologically. Selected transcripts and protein products will be monitored by single-cell PCR and immunohistochemistry at defined times after retroviral marking to determine their precise onset of expression. Retrovirally-expressed shRNAs directed against selected transcripts will be utilized to test whether they perturb functional properties of the integrated neurons. This project takes advantage of the combined expertise of the Goodman and Westbrook labs in genomics, transcription, and hippocampal circuitry. 1
Unlike most regions of the brain, the hippocampus produces new neurons well into adulthood-these newborn neurons may contribute to learning and memory, and their decrease during aging may be associated with cognitive decline. This project aims to elucidate the gene expression patterns of these cells within the intact mouse brain to understand what controls their maturation and determine how these transcriptional patterns change when the cells become integrated into pre-existing circuits. This information could lead to new approaches for increasing newborn neuron production and survival.