Multiple synapsin I messenger RNAs are differentially regulated during neuronal development.
Synapsin I is a neuron-specific protein consisting of two isoforms Ia and Ib. It is thought to play a role in the regulation of neurotransmitter release. In this study the structure and expression of two classes of synapsin I mRNA have been examined. The two mRNA classes have molecular sizes of 3.4 and 4.5 kb, respectively. Both classes translate into synapsin I polypeptides and display a high degree of base sequence homology. Utilizing an oligonucleotide-directed RNase H assay we have shown that both mRNA classes have a common start site of transcription and differ from one another toward their 3' ends. The expression of the two synapsin I mRNA classes is differentially regulated during the development of the rat brain and cerebellum. In the cerebellum the 4.5-kb transcript is expressed until postnatal day 7, after which it decreases to an undetectable level. The 3.4-kb mRNA is found throughout cerebellar development and in the adult. This suggests that the 3.4-kb mRNA class consists of messages which can encode both synapsin I polypeptides. Using quantitative Northern blot analysis a peak in the expression of this mRNA was observed at postnatal day 20. The maximum expression of the 3.4-kb class coincides with the period of synaptogenesis in the cerebellum. In addition to the developmental time course of synapsin mRNA expression a description of its spatial distribution throughout the cerebellum was performed using in situ hybridization histochemistry. From postnatal day 15 onwards, with a maximum at postnatal day 20, synapsin mRNA was localized in the internal granule cell layer of the cerebellum. On a cellular level, the granule cells, but not the neighboring Purkinje cells, express high levels of synapsin mRNA. These observations implicate developmentally coordinated differential RNA splicing in the regulation of neuron-specific gene expression and substantiate the correlation of synapsin gene expression with the period of synaptogenic differentiation of neurons.
Haas
C A
CA
Department of Neurochemistry, Max Planck Institute for Psychiatry, Martinsried, Federal Republic of Germany.
DeGennaro
L J
LJ
D000818:Animals; D002454:Cell Differentiation; D002531:Cerebellum / Q000254:growth & development*; D003001:Cloning, Molecular; D004722:Endoribonucleases; D005786:Gene Expression Regulation; D009419:Nerve Tissue Proteins / Q000235:genetics*; D009474:Neurons / Q000166:cytology*; D009693:Nucleic Acid Hybridization; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D016914:Ribonuclease H; D013569:Synapses / Q000502:physiology; D016704:Synapsins
D009419:Nerve Tissue Proteins; D012333:RNA, Messenger; D016704:Synapsins; D004722:Endoribonucleases; D016914:Ribonuclease H