Gene expression is dynamically regulated by chromatin modifications on histone tails, such as acetylation. In general, histone acetylation promotes transcription, whereas histone deacetylation negatively regulates transcription. The interplay between histone acetyl-transerases and histone deacetylases (HDACs) is pivotal for the regulation of gene expression required for long-term memory processes. Currently, very little is known about the role of individual HDACs in learning and memory. We examined the role of HDAC3 in long-term memory using a combined genetic and pharmacologic approach. We used HDAC3–FLOX genetically modified mice in combination with adeno-associated virus-expressing Cre recombinase to generate focal homozygous deletions of Hdac3 in area CA1 of the dorsal hippocampus. To complement this approach, we also used a selective inhibitor of HDAC3, RGFP136 [N-(6-(2-amino-4-fluorophenylamino)-6-oxohexyl)-4-methylbenzamide]. Immunohistochemistry showed that focal deletion or intrahippocampal delivery of RGFP136 resulted in increased histone acetylation. Both the focal deletion of HDAC3 as well as HDAC3 inhibition via RGFP136 significantly enhanced long-term memory in a persistent manner. Next we examined expression of genes implicated in long-term memory from dorsal hippocampal punches using quantitative reverse transcription-PCR. Expression of nuclear receptor subfamily 4 group A, member 2 (Nr4a2) and c-fos was significantly increased in the hippocampus of HDAC3–FLOX mice compared with wild-type controls. Memory enhancements observed in HDAC3–FLOX mice were abolished by intrahippocampal delivery of Nr4a2 small interfering RNA, suggesting a mechanism by which HDAC3 negatively regulates memory formation. Together, these findings demonstrate a critical role for HDAC3 in the molecular mechanisms underlying long-term memory formation.

Nonspecific histone deacetylase (HDAC) inhibition has been shown to facilitate the extinction of drug-seeking behavior in a manner resistant to reinstatement. A key open question is which specific HDAC is involved in the extinction of drug-seeking behavior. Using the selective HDAC3 inhibitor RGFP966, we investigated the role of HDAC3 in extinction and found that systemic treatment with RGFP966 facilitates extinction in mice in a manner resistant to reinstatement. We also investigated whether the facilitated extinction is related to the enhancement of extinction consolidation during extinction learning or to negative effects on performance or reconsolidation. These are key distinctions with regard to any compound being used to modulate extinction, because a more rapid decrease in a defined behavior is interpreted as facilitated extinction. Using an innovative combination of behavioral paradigms, we found that a single treatment of RGFP966 enhances extinction of a previously established cocaine-conditioned place preference, while simultaneously enhancing long-term object-location memory within subjects. During extinction consolidation, HDAC3 inhibition promotes a distinct pattern of histone acetylation linked to gene expression within the infralimbic cortex, hippocampus, and nucleus accumbens. Thus, the facilitated extinction of drug-seeking cannot be explained by adverse effects on performance. These results demonstrate that HDAC3 inhibition enhances the memory processes involved in extinction of drug-seeking behavior.long-term memory | epigenetics | chromatin N umerous studies have demonstrated that long-term memory mechanisms require transcription (1), likely because gene expression is necessary for the stable changes in neuronal plasticity ultimately driving long-term changes in behavior. A key mechanism by which gene expression profiles are regulated is chromatin modification. One of the best-studied chromatin modifying mechanisms is histone acetylation, carried out by histone acetyltransferases and histone deacetylases (HDACs), which in general facilitate and repress gene expression, respectively (2-4). Several studies have demonstrated that manipulating histone acetyltransferases and HDACs can alter memory processes during initial memory formation (5-13) as well as extinction memory processes (14-17). Extinction is a transcription-dependent process (18-20) through which a previously held conditioned response (such as drug-seeking) is reduced or eliminated.Recently, it was reported that pharmacologic inhibition of HDACs facilitates extinction of drug-seeking, resulting in rapid and persistent loss of a previously established behavior that is resistant to reinstatement (16,21). One interpretation of this action is that HDAC inhibition robustly enhances consolidation of extinction memory, suggesting that HDACs normally function as negative regulators of extinction learning, similar to their role in initial memory consolidation. However, the finding that inhibition of HDACs during consolidation of extinction p...

No abstract

The principal neutralizing determinant of human immunodeficiency virus type 1 (IIV-1) is located in the external envelope protein, gpl20, and has previously been mapped to a 24-amino acid-long sequence (denoted RP135). We show here that deletion of this sequence renders the envelope unable to elicit neutralizing antibodies. In addition, using synthetic peptide fragments of RP135, we have mapped the neutralizing determinant to 8 amino acids and found that a peptide ofthis size elicits neutralizing antibodies. This sequence contains a central Gly-Pro-Gly that is generally conserved between different HIV-1 isolates and is flanked by amino acids that differ from isolate to isolate. Antibodies elicited by peptides from one isolate do not neutralize two different isolates, and a hybrid peptide, consisting of amino acid sequences from two isolates, elicits neutralizing antibodies to both isolates. By using a mixture of peptides of this domain or a mixture of such hybrid peptides the type-specificity of the neutralizing antibody response to this determinant can perhaps be overcome.

The human immunodeficiency virus type 1 (HIV-1) genome encodes the regulatory protein Rev, of relative molecular mass 13,000, which is synthesized from fully processed viral transcripts before synthesis of HIV-1 structural proteins. Rev has been postulated to exert control within the nucleus at the level of messenger RNA processing. The availability of Rev in the nucleus serves to increase the proportion of unspliced and singly spliced mRNA species relative to fully spliced mRNA molecules, resulting in an increased synthesis of viral structural proteins. A highly conserved cis-acting sequence termed the Rev-responsive element (RRE) has been identified in the envelope gene (env) of the viral transcript that seems to control mRNA processing in a Rev-dependent manner. Genetic studies have identified rev gene mutants with dominant phenotypes, supporting the hypothesis that Rev interacts directly with the RRE. Here we demonstrate that Rev protein, purified from Escherichia coli, binds in a sequence-specific manner to the RRE element in vitro.