Tissue expression and subcellular localization of CLN3, the Batten disease protein

Juvenile neuronal ceroid lipofuscinosis (Batten disease) is a progressive neurologic disorder which results from mutations in the CLN3 gene, which normally produces a 48-kDa polypeptide of unknown function. To help characterize the CLN3 protein, we have studied its tissue distribution and subcellular localization in human tissues using three epitope-specific polyclonal antibodies to human CLN3 by immunoblot, immunocytochemical, and immunoelectron microscopic analysis. The most abundant CLN3 protein expression was in the gray matter of the brain, where it was localized to astrocytes, capillary endothelium, and neurons. CLN3 was also evident in peripheral nerve, in pancreatic islet cells, and within the seminiferous tubules in the testis. Staining was generally diffuse within the cytoplasm with some nuclear reactivity. Subcellular localization identified the CLN3 protein within the nucleus and along cell membranes. These results were contrasted with the cellular distribution of palmitoyl-protein thioesterase (PPT), the enzyme whose deficiency is responsible for infantile neuronal ceroid lipofuscinosis (CLN1). PPT was most abundant in brain and visceral macrophages where it displayed a coarse granular staining pattern typical of lysosomal distribution. Immunoelectron microscopy confirmed that PPT immunoreactivity was limited to lysosomes.