Differential expression of SNAP-25a and SNAP-25b RNA transcripts in cranial nerve nuclei

Synaptosomal-associated protein of 25 kDa (SNAP-25) is involved in the mole cular regulation of neurotransmitter release. SNAP-25 exists in two isoform s, SNAP-25a and SNAP-25b, which arise from alternate splicing and which are differentially expressed throughout the nervous system. In situ hybridizat ion was used to examine the presence and subcellular localization of SNAP-2 5a and SNAP-25b RNA transcript expression in motor and parasympathetic nucl ei associated with cranial nerves. SNAP-25a RNA transcripts were strongly e xpressed in the parasympathetic Edinger-Westphal nucleus and dorsal motor n ucleus of the vagus nerve but weakly expressed in motor nuclei such as the oculomotor, trochlear, trigeminal, facial, ambiguus, hypoglossal and access ory nuclei and in motoneurons of mouse lumbar spinal cord. In contrast, SNA P-25b RNA transcripts were not detectable in the Edinger-Westphal nucleus a nd dorsal motor nucleus of the vagus nerve but were strongly expressed in t he oculomotor, trochlear, trigeminal, facial, ambiguus, hypoglossal, and ac cessory nuclei and in the motoneurons of mouse lumbar spinal cord. In the p arasympathetic cranial nerve nuclei, displaying high levels of SNAP-25a RNA transcripts, the labeling was cytoplasmic, whereas the labeling was nuclea r in the cranial nerve motor nuclei, displaying lower levels of transcripts . In contrast, labeling of SNAP-25b RNA transcripts was cytoplasmic in cran ial nerve motor nuclei and not detectable in parasympathetic cranial nerve nuclei. Possible explanations for the region-specific and differential subc ellular localization of SNAP-25a and SNAP-25b RNA transcripts are discussed . (C) 1999 Wiley-Liss, Inc.