Deep sequencing and high-resolution imaging reveal compartment-specific localization of Bdnf mRNA in hippocampal neurons

Brain-derived neurotrophic factor (BDNF) is a small protein of the neurotrophin family that regulates various brain functions. Although much is known about how its transcription is regulated, the abundance of endogenous BDNF mRNA and its subcellular localization pattern are matters of debate. We used next-generation sequencing and high-resolution in situ hybridization in the rat hippocampus to reexamine this question. We performed 3' end sequencing on rat hippocampal slices and detected two isoforms of Bdnf containing either a short or a long 3' untranslated region (3'UTR). Most of the Bdnf transcripts contained the short 3'UTR isoform and were present in low amounts relative to other neuronal transcripts. Bdnf mRNA was present in the somatic compartment of rat hippocampal slices or the somata of cultured rat hippocampal neurons but was rarely detected in the dendritic processes. Pharmacological stimulation of hippocampal neurons induced Bdnf expression but did not change the ratio of Bdnf isoform abundance. The findings indicate that endogenous Bdnf mRNA, although weakly abundant, is primarily localized to the somatic compartment of hippocampal neurons. Both Bdnf mRNA isoforms have shorter half-lives compared with other neuronal mRNAs. Furthermore, the findings show that using complementary high-resolution techniques can provide sensitive measures of endogenous transcript abundance.