Partial characterisation of murine huntingtin and apparent variations in the subcellular localisation of huntingtin in human, mouse and rat brain

Huntington's disease (HD) is an inherited neurodegenerative disorder causedby the expansion of a CAG repeat in a gene coding for a protein of unknownfunction. We have raised a polyclonal antibody against a 12 amino acidpeptide (residues 2110-2121 of human huntingtin) which specificallyrecognises huntingtin on Western blots of human, rat and mouse brain. Wehave characterised huntingtin expression in the mouse. The protein wasdetected on Western blots of all mouse tissues examined, with the highestexpression seen in brain. Human, mouse and rat brain were fractionated bydifferential centrifugation and discontinuous Percoll gradients. Thefractions were analysed by Western blotting for huntingtin andsynaptophysin (a synaptic vesicle localised protein). In mouse brain,huntingtin was localised in the soluble S3 fraction; in rat brain it waslocalised in the soluble S3 fraction and also in the membrane P2 and P3fractions; in both normal and HD- affected human brain, huntingtin wasmembrane bound with a distribution essentially the same as that ofsynaptophysin. These observed differences in the subcellular localisationof huntingtin between mouse and human brain are important in the context ofmouse models for HD.