The primary focus of research in the Abel lab is to understand the cellular and molecular mechanisms of long-term memory storage with a focus on the mammalian hippocampus. One of the hallmarks of long-term memory storage is that it requires the synthesis of new genes and new proteins, which act to alter the strength of synaptic connections within appropriate neuronal circuits in the brain. How are the various signals acting on a neuron integrated to give rise to appropriate changes in gene expression? How are changes in gene expression maintained to sustain memories for days, months and even years? In our lab, we have focused on transcriptional co-activators such as CREB-binding protein (CBP) and p300, leading us to investigate the effects of histone acetylation and other epigenetic modifications in memory storage. Increasing histone acetylation pharmacologically by inhibiting histone deacetylase (HDAC) enzymes during memory consolidation enhances long-term memory. Of particular importance is the identification of genes regulated by epigenetic mechanisms during memory consolidation and after HDAC inhibition using next-generation sequencing technology. Signals from synapses drive the transcriptional processes that are required for memory storage. A major challenge in the study of these synaptic signals is how the pathway specificity of synaptic plasticity is maintained in the face of diffusible second messengers, such as cyclic AMP (cAMP), and diffusible proteins, such as the catalytic subunit of protein kinase A (PKA). We are investigating the role of A-kinase anchoring proteins (AKAPs), which restrict PKA to specific subcellular locations, to define how signal transduction pathways in neurons are able to exhibit spatial specificity.
We are also investigating processes that can modulate the consolidation of long-term memory. For example, the biological function of sleep has remained elusive, but studies suggest that one function of sleep may be to mediate memory storage. First, sleep appears to facilitate the formation of hippocampus-dependent memories, and sleep is increased following training. Second, sleep appears to be regulated by many of the same molecular processes that contribute to memory storage, including the transcription factor cAMP response element-binding protein (CREB) and the PKA signaling pathway. By using conditional genetic approaches and gene expression studies, we are striving to elucidate the machinery underlying sleep/wake regulation and define the role of sleep in the consolidation of long-term memory. Our studies also reveal that sleep deprivation impairs memory consolidation and synaptic plasticity by impairing signaling through the cAMP pathway.
Cognitive deficits accompany many neurological, psychiatric and neurodevelopmental disorders. We are interested in determining how our knowledge of the cellular and molecular mechanisms of synaptic plasticity and memory storage can help us understand the cognitive deficits that are seen in patients with schizophrenia, autism and intellectual disability. Recent evidence suggests that disturbances in specific intracellular signaling pathways may contribute to schizophrenia. Studies in humans indicate that activity within the cAMP/PKA signaling pathway may be increased in the central nervous systems of schizophrenia patients, and our work suggests that this pathway plays a role in endophenotypes of schizophrenia in mice. With these translational approaches, we hope to identify novel targets for the development of new therapeutics to treat psychiatric and neurodevelopmental disorders.
CaMKII-Cre (line L7ag#13) mice were a kind gift from Dr. Ioannis Dragatsis (University of Tennessee). The construct was composed of the 8.5 kb 5' flanking calcium/calmodulin-dependent protein kinase II gene (CaMKII-alpha) promoter fragment, a short synthetic intron, a Cre recombinase gene containing a nuclear localization sequence, and a poly(A) addition sequence. Transgenic constructs were injected into CBA X C57BL/6J fertilized eggs and founders were crossed with C57BL/6J mice.
These mice express Cre recombinase, under the control of the CaMKII-alpha promoter, postnatally in excitatory forebrain neurons (cortex, striatum, amygdala, Hippocampal CA1, CA3, and DG). A moderate level of Cre was also detected in testis, similar to the amount of Cre in the cerebellum, at P30 and P120.
CaMKII-Cre (line R4ag#11) mice were a kind gift from Dr. Ioannis Dragatsis (University of Tennessee). The construct was composed of the 8.5 kb 5' flanking calcium/calmodulin-dependent protein kinase II gene (CaMKII-alpha) promoter fragment, a short synthetic intron, a Cre recombinase gene containing a nuclear localization sequence, and a poly(A) addition sequence. Transgenic constructs were injected into CBA X C57BL/6J fertilized eggs and founders were crossed with C57BL/6J mice.
These mice express Cre recombinase, under the control of the CaMKII-alpha promoter, postnatally in excitatory forebrain neurons (cortex, striatum, amygdala, hippocampal CA1 and DG).
Nr4a family gene expression increases within the hippocampus after training in a hippocampus-dependent task. The dominant-negative form of NR4A1 (NR4ADN) contains the DNA-binding and dimerization domains but lacks the transactivation domain. It silences the three Nr4a family members.
We generated a transgenic mouse line expressing the NR4ADN construct under control of the tetracycline operator (tetO), which we combined with the CaMKII–tetracycline transactivator (CaMKII-tTA) transgene to achieve expression selectively within postnatal excitatory forebrain neurons. The dominant-negative protein interacts with NR4A proteins in vivo.
Transgene expression was restricted in the forebrain to the striatum, sparse cortical areas, and subregions of the hippocampal formation (CA1 and the dentate gyrus). Transgene expression was not observed in the amygdala or in area CA3 of the hippocampus.
Nr4a polymorphisms have been identified in patients with schizophrenia, and Nr4a gene expression is reduced in patients with schizophrenia. Thus, impaired Nr4a function may contribute to the cognitive impairments that accompany this psychiatric disorder.