Calpain/chemistry; Caspases/metabolism; Cell Nucleus/metabolism; Nerve Tissue Proteins/chemistry; Nuclear Proteins/chemistry; Amino Acid Sequence; Animals; Binding Sites; Blotting, Western; Calcium/metabolism; Calpain/metabolism; Calpain/physiology; Cell Line; Cells, Cultured; Cloning, Molecular; Cytoplasm/metabolism; DNA, Complementary/metabolism; Disease Progression; Epitopes; Humans; Huntingtin Protein; Huntington Disease/metabolism; Mice; Mice, Transgenic; Microscopy, Fluorescence; Molecular Sequence Data; Mutagenesis, Site-Directed; Mutation; Peptides; Plasmids/metabolism; Precipitin Tests; Protein Structure, Tertiary; RNA, Messenger/metabolism; Reverse Transcriptase Polymerase Chain Reaction; Signal Transduction; Thapsigargin/chemistry