FAD‐linked sulfhydryl oxidase QSOX: Topographic, cellular, and subcellular immunolocalization in adult rat central nervous system

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Abstract
The distribution of the sulfhydryl oxidase QSOX in the rat brain was mapped using immunohistochemistry. QSOX is specifically expressed by neurons throughout the rostrocaudal extent of the brain as well as in the spinal cord. Although a majority of neurons express QSOX, different intensities of labeling were observed depending on the area: the strongest labeling was observed in the olfactory bulbs, isocortex, hippocampus, basal telencephalon, several thalamic and hypothalamic nuclei, cerebellum, and numerous brainstem nuclei. This study also describes the ultrastructural localization of QSOX in neuronal cells and demonstrates that the enzyme is associated with the Golgi apparatus. Finally, selected double immunohistochemistry showed that in the hypothalamus the highest levels of QSOX labeling were colocalized in neuron populations that express disulfide‐bounded neuropeptides. These observations are consistent with a role of the enzyme in secreted peptide/protein folding. Data presented herein will serve as a basis for further investigations of the physiological function of QSOX in the central nervous system. J. Comp. Neurol. 473:334–363, 2004.