GSE115718
Transcriptional profiling in Kenyon cells reveals dynamic regulation of learning and memory genes after acquisition of long-term courtship memory
Purpose: The formation and recall of long term memory (LTM) requires neuron activity induced gene expression. Transcriptome analysis has been used to identify genes that have altered expression after memory acquisition, however, we still have an incomplete picture of the transcriptional changes that are required for LTM formation. The complex spatial and temporal dynamics of memory formation creates significant challenges in defining memory-relevant gene expression changes. The mushroom body (MB) is a signaling hub in the insect brain that integrates sensory information to form memories. Our study looks to further elucidate the transcriptional mechanisms underlying LTM by profiling gene expression changes in nuclei of the MB during a time course of LTM formation. Methods: We isolated and sequenced fly RNA from biologically paired whole head (WH) and mushroom body (MB) nuclei. MB nuclei were isolated using INTACT (isolation of nuclei tagged in a specific cell type). LTM was induced using a seven-hour courtship conditioning protocol. Fly heads were collected one hour and 24-hours after this period of sexual rejection. Samples of naive, socially isolated males were also collected at the same age and time-of-day for comparison. Results and conclusions: We identified more transcriptional changes 1 hour after memory acquisition (WH = 322, MB = 305) than at 24 hours (WH = 20, MB = 24). WH samples showed downregulation of developmental genes and upregulation of sensory response genes. In contrast, MB samples showed vastly different gene expression changes affecting biological processes that are specifically related to LTM.  MB-downregulated genes were highly enriched for metabolic function, consistent with the MB-specific energy influx that occurs during LTM formation. MB-upregulated genes were highly enriched for known learning and memory processes, including calcium mediated neurotransmitter release and cAMP signalling. The neuron activity inducible genes hr38 and sr were also specifically induced in the MB. These results highlight the importance of sampling time and cell type in capturing biologically relevant transcriptional changes involved in learning and memory. Our data suggests that MB cells transiently upregulate known memory related pathways after memory acquisition, and provides a critical frame of reference for further investigation into the role MB-specific gene regulation in memory. Overall design: Nuclear RNA profiles with >10 million genic reads were generated for both whole head samples (five naïve, three 1h-AR, four 24h-AR) and mushroom body samples (four naïve, four 1h-AR, four 24h-AR).