Mol Neurodegener. 2010 May 27;5(1):22. Localization of BDNF mRNA with the Huntington's disease protein in rat brain.  Ma B, Culver BP, Baj G, Tongiorgi E, Chao MV, Tanese N. Exploring the role of mRNA in HD By Carly Desmond, June 2010 Although mutant huntingtin protein is expressed in all tissues of the body, Huntington’s Disease (HD) primarily affects neurons in the striatum of the brain, and subsequently the cerebral cortex.  There have been many proposed hypotheses as to why neurons, and particularly the neurons of the striatum, are so susceptible to toxicity in the disease.  One long standing idea is that mutant huntingtin causes the striatal neurons to become starved for Brain Derived Neurotropic Factor (BDNF).  BDNF is typically delivered to the striatum from the neighbouring cerebral cortex, and is responsible for encouraging neuron survival, growth and development and making new synaptic connections which are necessary for learning and memory.  Past explanations for the deficiency of BDNF in the striatum in HD have been that BDNF mRNA transcription is adversely affected by mutant huntingtin and that the delivery of BDNF from the cortex is impaired.  In this new paper, the authors have suggested that a third possibility may exist, whereby mutant huntingtin disrupts BDNF at the level of mRNA processing and transport.  Neurons are an extremely specialized cell type, with long projecting axons and dendrites.  To ensure that particular proteins are expressed only at the location they are intended to function, their mRNA transcripts are often repressed, transported to their destination and only then translated to protein.  Some BDNF mRNA transcripts are thought to follow this path, traveling from the nucleus to the dendrites of neurons prior to translation.  What was done here: After several previous studies where Naoko Tanese’s group described a new association of huntingtin with Ago 2 (a protein involved in mRNA silencing), as well as with neuronal transport granules, they decided to explore whether or not huntingtin might interact with BDNF mRNA.  Using older techniques, as well as a novel, improved 3D method for imaging thick tissue sections, the authors reported a co-localization between huntingtin protein and BDNF mRNA in dendrites, in both cell culture and in real rat cortical tissue.  Why this is important: Since mRNA transport granules often have the capability to move a variety of transcripts, these studies suggest that other localized mRNAs could be disrupted by mutant huntingtin. However, it remains to be seen how big a role mRNA transport deficiencies could play in HD.  Interestingly, mutant mouse models with impaired BDNF mRNA transport are reported to have reduced branching of dendrites and increased anxiety. These findings further suggest the importance of localized BDNF translation to HD, as well as other neurodegenerative diseases.