Marquèze B, Boudier J A, Mizuta M, Inagaki N, Seino S, Seagar M
INSERM U 374, Institut Jean Roche, Faculté de Médecine-Nord, Marseille, France.
J Neurosci. 1995 Jul;15(7 Pt 1):4906-17. doi: 10.1523/JNEUROSCI.15-07-04906.1995.
Three isoforms of synaptotagmin, a synaptic vesicle protein involved in neurotransmitter release, have been characterized in the rat, although functional differences between these isoforms have not been reported. In situ hybridization was used to define the localization of synaptotagmin I, II, and III transcripts in the rat CNS and pituitary and adrenal glands. Each of the three synaptotagmin genes has a unique expression pattern. The synaptotagmin III gene is expressed in most neurons, but transcripts are much less abundant than the products of the synaptotagmin I and II genes. A majority of neurons in the forebrain expressed both synaptotagmin I and III mRNAs while synaptotagmin II gene expression was confined to subsets of neurons in layers IV-VI of the cerebral cortex, in the dentate granule cell region, the hilus, and the CA1-CA3 areas of the hippocampus. In the cerebellum, all three transcripts were visualized in the granule cell layer. Furthermore, synaptotagmin I probes revealed striking differences between distinct populations of neurons, as in addition to moderate labeling of granule cells, much more prominent hybridization signals were detected on scattered cell bodies likely to be Golgi interneurons. In the most caudal part of the brain, synaptotagmin II transcripts were abundant and were coexpressed with synaptotagmin III mRNAs. This pattern was found in putative motoneurons of the spinal cord, suggesting that the two isoforms might be involved in exocytosis at the neuromuscular junction. Only synaptotagmin I mRNAs were detected in the anterior and intermediate pituitary and in adrenal medullary cells. These data reveal an unexpectedly subtle segregation of the expression of synaptotagmin genes and the existence of multiple combinations of synaptotagmin isoforms which may provide diversity in the regulation of neurosecretion.
突触结合蛋白是一种参与神经递质释放的突触小泡蛋白，在大鼠中已鉴定出三种同工型，尽管尚未报道这些同工型之间的功能差异。原位杂交用于确定突触结合蛋白I、II和III转录本在大鼠中枢神经系统、垂体和肾上腺中的定位。三种突触结合蛋白基因各有独特的表达模式。突触结合蛋白III基因在大多数神经元中表达，但转录本的丰度远低于突触结合蛋白I和II基因的产物。前脑中的大多数神经元同时表达突触结合蛋白I和III的mRNA，而突触结合蛋白II基因的表达局限于大脑皮层IV-VI层、齿状颗粒细胞区域、海马回和海马体CA1-CA3区域的神经元亚群。在小脑中，所有三种转录本都在颗粒细胞层中可见。此外，突触结合蛋白I探针揭示了不同神经元群体之间的显著差异，除了颗粒细胞有适度标记外，在可能是高尔基中间神经元的散在细胞体上检测到更为突出的杂交信号。在脑的最尾端部分，突触结合蛋白II转录本丰富，并与突触结合蛋白III的mRNA共表达。这种模式在脊髓的假定运动神经元中发现，表明这两种同工型可能参与神经肌肉接头处的胞吐作用。仅在垂体前叶和中叶以及肾上腺髓质细胞中检测到突触结合蛋白I的mRNA。这些数据揭示了突触结合蛋白基因表达出人意料的细微分离以及突触结合蛋白同工型多种组合的存在，这可能为神经分泌调节提供多样性。
