Biology subjects

Greer, C. B.

Publications and source records attributed to Greer, C. B..

3 recordsLinked to original sources

bioRxiv2024

HEXIM1 is correlated with Alzheimer's disease pathology and regulates immediate early gene dynamics in neurons

Cognitive processes require de novo gene transcription in neurons. Memory requires the rapid and robust transcription of a class of genes called immediate early genes (IEGs). IEG transcription is facilitated by the formation of a poised basal state, in which RNA polymerase II (RNAP2) initiates transcription, but remains paused downstream of the promoter. Upon neuronal depolarization, the paused RNAP2 is released to complete the synthesis of messenger RNA (mRNA) transcripts, a process stimulated by positive transcription elongation factor b (P-TEFb). In many cell types, P-TEFb is sequestered into a large inactive complex containing Hexamethylene bisacetamide inducible 1 (HEXIM1), but the impact of this interaction on neuronal gene transcription is not yet fully understood. In this study, we found that neuronal expression levels of HEXIM1 mRNA are highly correlated with impaired cognition in Alzheimers disease. It is also induced in the hippocampus during memory formation, and following depolarization in neurons. The role of HEXIM1 in neuronal gene transcription was then explored in murine neuronal cultures where we found that calcium frees P-TEFb from the HEXIM1 inhibitory complex. Modulation of P-TEFb by inhibiting the activity of the cyclin-dependent kinase 9 (CDK9) subunit of this complex significantly impacts IEG induction, particularly during repeated depolarization. Our findings indicate that HEXIM1 in complex with P-TEFb plays an important role in establishing and resetting the poised RNAP2 state, enabling efficient activation of genes necessary for synaptic plasticity.

neuroscience↗

bioRxiv2020

Tet1 isoforms differentially regulate gene expression, synaptic transmission and memory in the mammalian brain.

The dynamic regulation of DNA methylation in post-mitotic neurons is necessary for memory formation and other adaptive behaviors. Ten-eleven translocation 1 (TET1) plays a part in these processes by oxidizing 5-methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC), thereby initiating active DNA demethylation. However, attempts to pinpoint its exact role in the nervous system have been hindered by contradictory findings, perhaps due in part, to a recent discovery that two isoforms of the Tet1 gene are differentially expressed from early development into adulthood. Here, we demonstrate that both the shorter transcript (Tet1S) encoding an N-terminally truncated TET1 protein and a full-length Tet1 (Tet1FL) transcript encoding canonical TET1 are co-expressed in the adult brain. We show that Tet1S is the predominantly expressed isoform, and is highly enriched in neurons, whereas Tet1FL is generally expressed at lower levels and more abundant in glia, suggesting their roles are at least partially cell-type specific. Using viral-mediated, isoform- and neuron-specific molecular tools, we find that Tet1S repression enhances, while Tet1FL impairs, hippocampal-dependent memory. In addition, the individual disruption of the two isoforms leads to contrasting changes in basal synaptic transmission and the dysregulation of unique gene ensembles in hippocampal neurons. Together, our findings demonstrate that each Tet1 isoform serves a distinct role in the mammalian brain.

neuroscience↗

bioRxiv2019

An antisense oligonucleotide leads to suppressed transcriptional elongation of Hdac2 and long-term memory enhancement

Repression of the memory suppressor gene histone deacetylase 2 (Hdac2) in mice elicits cognitive enhancement, and drugs that block HDAC2 catalytic activity are being investigated for treating disorders affecting memory. Currently available compounds that target HDAC2 are not specific to the HDAC2 isoform, and have short half-lives. Antisense oligonucleotides (ASOs) are a class of drugs that base pair with RNA targets and exhibit extremely long-lasting, specific inhibition relative to small molecule drugs. We utilized an ASO to reduce Hdac2 messenger RNA (mRNA) quantities, and explored its longevity, specificity, and mechanism of repression. A single injection of the Hdac2-targeted ASO in the central nervous system diminished Hdac2 mRNA levels for at least 4 months in the brain, and knockdown of this factor resulted in significant memory enhancement for 8 weeks in mice. RNA-seq analysis of brain tissues revealed that the ASO repression was specific to the Hdac2 isoform relative to other classical Hdac genes, and caused alterations in levels of other memory-associated mRNAs. In cultured neurons, we observed that the Hdac2-targeted ASO suppressed Hdac2 mRNA and an Hdac2 non-coding regulatory extra-coding RNA (ecRNA). The ASO not only triggered a reduction in mRNA levels, but also elicited direct transcriptional suppression of the Hdac2 gene through blocking RNA polymerase II elongation. These findings suggest transcriptional suppression of the target gene as a novel mechanism of action of ASOs, and opens up the possibility of using ASOs to achieve lasting gene silencing in the brain without altering the nucleotide sequence of a gene.

pharmacology and toxicology↗