The vertebrate brain-derived neurotrophic factor (BDNF) gene produces a number of alternatively spliced transcripts only some of which generate the BDNF protein required for synaptic plasticity and learning. Many of the transcripts are uncharacterized and are of unknown biological significance. Previously, we described alternative splicing within the protein-coding sequence of the BDNF gene in the pond turtle (tBDNF) that generates a functionally distinct truncated protein isoform (trcBDNF) that is regulated during a neural correlate of eyeblink classical conditioning in ex vivo brainstem preparations. We hypothesized that trcBDNF has a dominant negative function because of its anticorrelated expression pattern compared to its full-length BDNF counterpart. The data presented here suggests that trcBDNF functions as a transcriptional repressor of a conditioning-inducible downstream tBDNF promoter that controls expression of full-length BDNF required for learning. First, expression of full-length transcripts is negatively correlated with trcBDNF; transcripts are inhibited when endogenous trcBDNF is ectopically induced and expressed when trcBDNF is inhibited. Second, ChIP-qPCR assays of a recombinant trcBDNF protein, RtrcBDNF, show strong binding to the downstream tBDNF exon III promoter that corresponds with inhibition of conditioning. Third, deletions of the C-terminus of RtrcBDNF result in inhibition of promoter binding and conditioning acquisition when a tropomyosin receptor kinase B (TrkB) binding site is accounted for. Finally, microinjection of RtrcBDNF directly into brainstem preparations inhibits conditioning. These data reveal a new mechanism of activity-dependent BDNF transcriptional regulation and suggest that BDNF is an autoregulatory gene. How generalizable this mechanism is across plasticity genes remains to be elucidated.

脊椎动物脑源性神经营养因子 ( BDNF ) 基因会产生许多选择性剪接的转录物，其中只有一些会产生突触可塑性和学习所需的 BDNF 蛋白。许多转录本是未表征的并且具有未知的生物学意义。以前，我们描述了池塘龟 ( tBDNF) BDNF基因的蛋白质编码序列中的选择性剪接) 产生功能不同的截断蛋白同种型 (trcBDNF)，在离体脑干制剂中眨眼经典条件反射的神经相关过程中受到调节。我们假设 trcBDNF 具有显性负功能，因为与其全长 BDNF 对应物相比，它的反相关表达模式。此处提供的数据表明 trcBDNF 作为调节诱导型下游tBDNF的转录抑制因子起作用控制学习所需的全长 BDNF 表达的启动子。首先，全长转录本的表达与 trcBDNF 呈负相关；当内源性 trcBDNF 被异位诱导和表达时，转录物被抑制。其次，重组 trcBDNF 蛋白 RtrcBDNF 的 ChIP-qPCR 检测显示与下游tBDNF外显子 III 启动子的强结合，对应于条件反射的抑制。第三，当考虑到原肌球蛋白受体激酶 B (TrkB) 结合位点时，RtrcBDNF C 末端的缺失会导致启动子结合和调节获得的抑制。最后，将 RtrcBDNF 直接显微注射到脑干制剂中会抑制条件反射。这些数据揭示了一种活动依赖性BDNF的新机制转录调节并表明BDNF是一种自动调节基因。这种机制在可塑性基因中的普遍性还有待阐明。