Regulation ofBDNFchromatin status and promoter accessibility in a neural correlate of associative learning

Abstract

Brain-derived neurotrophic factor (BDNF) gene expression critically controls learning and its aberrant regulation is implicated in Alzheimer's disease and a host of neurodevelopmental disorders. The BDNF gene is target of known DNA regulatory mechanisms but details of its activity-dependent regulation are not fully characterized. We performed a comprehensive analysis of the epigenetic regulation of the turtle BDNF gene (tBDNF) during a neural correlate of associative learning using an in vitro model of eye blink classical conditioning. Shortly after conditioning onset, the results from ChIP-qPCR show conditioning-dependent increases in methyl-CpG-binding protein 2 (MeCP2) and repressor basic helix-loop-helix binding protein 2 (BHLHB2) binding to tBDNF promoter II that corresponds with transcriptional repression. In contrast, enhanced binding of ten-eleven translocation protein 1 (Tet1), extracellular signal-regulated kinase 1/2 (ERK1/2), and cAMP response element-binding protein (CREB) to promoter III corresponds with transcriptional activation. These actions are accompanied by rapid modifications in histone methylation and phosphorylation status of RNA polymerase II (RNAP II). Significantly, these remarkably coordinated changes in epigenetic factors for two alternatively regulated tBDNF promoters during conditioning are controlled by Tet1 and ERK1/2. Our findings indicate that Tet1 and ERK1/2 are critical partners that, through complementary functions, control learning-dependent tBDNF promoter accessibility required for rapid transcription and acquisition of classical conditioning.

MeCP2 regulates Tet1-catalyzed demethylation, CTCF binding, and learning-dependent alternative splicing of the BDNF gene in Turtle

“…These findings were specific to the 2a transcript as expression of the other three exon II transcripts were not significantly affected by YB-1 siRNA treatment ( tBDNF2b-d , F (1,28) = 0.10, p=0.75). Analysis of transcripts after application of a Tet1 siRNA to naïve preparations was previously reported in Ambigapathy et al (2015). These data are replotted here and show that Tet1 siRNA applied to naïve nearly completely suppressed the tBDNF2a transcript to only 4% of normal naïve values (Figure 3E, p=0.0003).…”

“…These data showed minimal binding in normal naïve preparations that was greatly increased after Tet1 siRNA treatment (Figure 5C, n = 3/group, p=0.001). The enhanced binding of Tet3 was not accompanied by any changes in protein expression (Ambigapathy et al, 2015). These ChIP data indicate that the MeCP2-YB-1 complex was not recruited to methylated DNA under conditions in which there is loss of Tet1, which is replaced by Tet3.

10.7554/eLife.25384.008Figure 5.Inhibition of Tet1 by siRNA alters methylation and blocks MeCP2 and YB-1 binding to the coding sequence.( A ) Methylation status of the tBDNF coding sequence (CpGs 2–11) in normal and Tet1 siRNA-treated naïve preparations analyzed by BSP.

…”

Tet1 overexpression leads to anxiety‐like behavior and enhanced fear memoriesviathe activation of calcium‐dependent cascade through Egr1 expression in mice

“…However, increased hippocampal proBDNF expression causes improper effects on the brain (41,42). Because BDNF is regulated by Tet1 directly in its promoter exon region, the elevated proBDNF expression in the hippocampus seems to be a direct consequence of Tet1 overexpression (43,44). Egr1 is a mediator of NMDA receptor signaling during AMPA receptor trafficking, which is required for long-term depression in hippocampal primary neurons (45).…”

Primetime for Learning Genes

“…This latter response triggers the expression of mature BDNF protein which initiates signaling mechanisms underlying conditioned learning in this preparation. Correspondingly, the promoter for exon II is rapidly methylated while, at the same time, promoter III is demethylated [ 62 ], as illustrated in Figure 1 B, which shows epigenetic modifications of tBDNF promoters in the naïve untrained and conditioned states. Enhanced binding of MeCP2 and transcriptional repressor basic helix-loop-helix binding protein 2 (BHLHB2) to tBDNF promoter II after conditioning ( Figure 1 B), demonstrated by chromatin immunoprecipitation and quantitative PCR (ChIP-qPCR), corresponds to the methylation.…”