Mutations in the gene for
aspartoacylase (ASPA), which catalyzes deacetylation of
N-acetyl-L-aspartate in the central nervous system (CNS), result in
Canavan Disease, a fatal dysmyelinating disease. Consistent with its role in supplying
acetate for myelin
lipid synthesis, ASPA is thought to be cytoplasmic. Here we describe the occurrence of ASPA within nuclei of rat brain and kidney, and in cultured rodent oligodendrocytes. Immunohistochemistry showed cytoplasmic and nuclear ASPA staining, the specificity of which was demonstrated by its absence from tissues of the
Tremor rat, an ASPA-null mutant. Subcellular fractionation analysis revealed low
enzyme activity against NAA in nuclear fractions from normal rats. Whereas two recent reports have indicated that ASPA exists as a dimer, size-exclusion chromatography of subcellular fractions showed ASPA is an active monomer in both subcellular fractions. Western blotting detected ASPA as a single 38 kD band. Because ASPA is small enough to passively diffuse into the nucleus, we constructed, expressed, and detected in COS-7 cells a
green fluorescent protein-human ASPA (GFP-hASPA) fusion
protein larger than the permissible size for the nuclear pore complex. GFP-hASPA was enzymatically active and showed mixed nuclear-cytoplasmic distribution. We conclude that ASPA is a regulated nuclear-cytoplasmic
protein that may have distinct functional roles in the two cellular compartments.