A HAT for sleep?: epigenetic regulation of sleep by Tip60 in Drosophila

Time to learn: The role of the molecular circadian clock in learning and memory

The circadian system plays an important role in aligning biological processes with the external time of day. A range of physiological functions are governed by the circadian cycle, including memory processes, yet little is understood about how the clock interfaces with memory at a molecular level. The molecular circadian clock consists of four key genes/gene families, Period, Clock, Cryptochrome, and Bmal1, that rhythmically cycle in an ongoing transcription-translation negative feedback loop that maintains an approximately 24-hour cycle within cells of the brain and body. In addition to their roles in generating the circadian rhythm within the brain's master pacemaker (the suprachiasmatic nucleus), recent research has suggested that these clock genes may function locally within memory-relevant brain regions to modulate memory across the day/night cycle. This review will discuss how these clock genes function both within the brain's central clock and within memory-relevant brain regions to exert circadian control over memory processes. For each core clock gene, we describe the current research that demonstrates a potential role in memory and outline how these clock genes might interface with cascades known to support long-term memory formation. Together, the research suggests that clock genes function locally within satellite clocks across the brain to exert circadian control over long-term memory formation and possibly other biological processes. Understanding how clock genes might interface with local molecular cascades in the hippocampus and other brain regions is a critical step toward developing treatments for the myriad disorders marked by dysfunction of both the circadian system and cognitive processes.

TIP60 in aging and neurodegeneration

Epigenetic modification of chromatin, including histone methylation and acetylation, plays critical roles in eukaryotic cells and has a significant impact on chromatin structure/accessibility, gene regulation and, susceptibility to aging, neurodegenerative disease, cancer, and other age-related diseases. This article reviews the current advances on TIP60/KAT5, a major histone acetyltransferase with diverse functions in eukaryotes, with emphasis on its regulation of autophagy, proteasome-dependent protein turnover, RNA transcription, DNA repair, circadian rhythms, learning and memory, and other neurological functions implicated in aging and neurodegeneration. Moreover, the promising therapeutic potential of TIP60 is discussed to target Alzheimer's disease and other neurological diseases.

Tip60 HAT Action Mediates Environmental Enrichment Induced Cognitive Restoration

Environmental enrichment (EE) conditions have beneficial effects for reinstating cognitive ability in neuropathological disorders like Alzheimer's disease (AD). While EE benefits involve epigenetic gene control mechanisms that comprise histone acetylation, the histone acetyltransferases (HATs) involved remain largely unknown. Here, we examine a role for Tip60 HAT action in mediating activity- dependent beneficial neuroadaptations to EE using the Drosophila CNS mushroom body (MB) as a well-characterized cognition model. We show that flies raised under EE conditions display enhanced MB axonal outgrowth, synaptic marker protein production, histone acetylation induction and transcriptional activation of cognition linked genes when compared to their genotypically identical siblings raised under isolated conditions. Further, these beneficial changes are impaired in both Tip60 HAT mutant flies and APP neurodegenerative flies. While EE conditions provide some beneficial neuroadaptive changes in the APP neurodegenerative fly MB, such positive changes are significantly enhanced by increasing MB Tip60 HAT levels. Our results implicate Tip60 as a critical mediator of EE-induced benefits, and provide broad insights into synergistic behavioral and epigenetic based therapeutic approaches for treatment of cognitive disorder.

Tip off the HAT- Epigenetic control of learning and memory by Drosophila Tip60

Disruption of epigenetic gene control mechanisms involving histone acetylation in the brain causes cognitive impairment, a debilitating hallmark of most neurodegenerative disorders. Histone acetylation regulates cognitive gene expression via chromatin packaging control in neurons. Unfortunately, the histone acetyltransferases (HATs) that generate such neural epigenetic signatures and their mechanisms of action remain unclear. Our recent findings provide insight into this question by demonstrating that Tip60 HAT action is critical for morphology and function of the mushroom body (MB), the learning and memory center in the Drosophila brain. We show that Tip60 is robustly produced in MB Kenyon cells and extending axonal lobes and that targeted MB Tip60 HAT loss results in axonal outgrowth disruption. Functional consequences of loss and gain of Tip60 HAT levels in the MB are evidenced by defects in memory. Tip60 ChIP-Seq analysis reveals enrichment for genes that function in cognitive processes and accordingly, key genes representing these pathways are misregulated in the Tip60 HAT mutant fly brain. Remarkably, increasing levels of Tip60 in the MB rescues learning and memory deficits resulting from Alzheimer's disease associated amyloid precursor protein (APP) induced neurodegeneration. Our studies highlight the potential of HAT activators as a therapeutic option for cognitive disorders.

Mating and memory: an educational primer for use with "epigenetic control of learning and memory in Drosophila by Tip60 HAT action"

An article by Xu et al. in the December 2014 issue of GENETICS can be used to illustrate epigenetic modification of gene expression, reverse genetic manipulation, genetic/epigenetic influence on behavioral studies, and studies using the Drosophila model organism applied to human disease. This Primer provides background information; technical explanations of genetic, biochemical, and behavioral approaches from the study; and an example of an approach for classroom use with discussion questions to aid in student comprehension of the research article.

Epigenetic control of learning and memory in Drosophila by Tip60 HAT action

Disruption of epigenetic gene control mechanisms in the brain causes significant cognitive impairment that is a debilitating hallmark of most neurodegenerative disorders, including Alzheimer's disease (AD). Histone acetylation is one of the best characterized of these epigenetic mechanisms that is critical for regulating learning- and memory- associated gene expression profiles, yet the specific histone acetyltransferases (HATs) that mediate these effects have yet to be fully characterized. Here, we investigate an epigenetic role for the HAT Tip60 in learning and memory formation using the Drosophila CNS mushroom body (MB) as a well-characterized cognition model. We show that Tip60 is endogenously expressed in the Kenyon cells, the intrinsic neurons of the MB, and in the MB axonal lobes. Targeted loss of Tip60 HAT activity in the MB causes thinner and shorter axonal lobes while increasing Tip60 HAT levels cause no morphological defects. Functional consequences of both loss and gain of Tip60 HAT levels in the MB are evidenced by defects in immediate-recall memory. Our ChIP-Seq analysis reveals that Tip60 target genes are enriched for functions in cognitive processes, and, accordingly, key genes representing these pathways are misregulated in the Tip60 HAT mutant fly brain. Remarkably, we find that both learning and immediate-recall memory deficits that occur under AD-associated, amyloid precursor protein (APP)-induced neurodegenerative conditions can be effectively rescued by increasing Tip60 HAT levels specifically in the MB. Together, our findings uncover an epigenetic transcriptional regulatory role for Tip60 in cognitive function and highlight the potential of HAT activators as a therapeutic option for neurodegenerative disorders.