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PubMed1991

Structure and function of the chromogranin A gene. Clues to evolution and tissue-specific expression.

Chromogranin A is the index member of a family of acidic proteins stored and released throughout the neuroendocrine system with peptide hormones and neurotransmitters. To better understand its functional domains, its evolutionary lineage, and the basis of its tissue-specific pattern of expression, we obtained a mouse chromogranin A cDNA and used it to isolate the chromogrannin A gene from the mouse genome. We then characterized the gene's exon/intron structure, and the structure and function of its 5'-regulatory region (promoter/enhancer). The chromogranin A gene was complex, its eight exons and seven introns spanning about 11 kilobase pairs. The eight exons displayed some correspondence to putative functional domains suspected within the cDNA-deduced primary structure of the protein. Three exons also displayed both length and sequence homology to exons in another member of the chromogranin/secretogranin family, chromogranin B, suggesting an evolutionary relationship. A 1.2-kilobase pair genomic fragment just 5' of the coding region was able to program cell type-specific gene expression in a transfection/reporter system. Both pituitary corticotropes and adrenal chromaffin cells recognized this promoter. The promoter possessed some known consensus transcriptional control elements (TATA box, cyclic AMP-response element, and Sp1 site), but otherwise novel transcriptional control elements seem to be operative. The results suggest that this complex gene is encoded by exon modules with evolutionary links to homologous modules in other chromogranin/secretogranin protein family members, and that the 5'-flanking region of the gene is sufficient to confer neuroendocrine tissue-specific expression of the chromogranin A gene.

Amino Acid Sequence↗
PubMed1989

Transmembrane topography and evolutionary conservation of synaptophysin.

Synaptophysin is the major integral membrane protein of small synaptic vesicles. Its primary structure deduced from rat and human complementary DNA sequences predicts that synaptophysin contains four transmembrane regions and a carboxyl-terminal domain having a novel repetitive structure. To elucidate the transmembrane organization of this protein in the synaptic vesicle, five antipeptide antibodies were raised. The site-specific antibodies were used to map the cognate sequences to the cytoplasmic or intravesicular side of the synaptic vesicle membrane by determining the susceptibility of the epitopes to proteolysis. The results confirm a topographic model for synaptophysin in which the protein spans the vesicle membrane four times, with both the amino and carboxyl terminus being cytoplasmic. In addition, the evolutionary conservation of the synaptophysin domains was addressed as a function of their membrane localization. To this end the primary structure of bovine synaptophysin was determined. Sequence comparisons between bovine, rat, and human synaptophysin revealed that only the intravesicular loops showed a significant number of amino acid substitutions (22%), while the transmembrane regions and cytoplasmic sequences were highly conserved (3% substitutions). These results depict synaptophysin as a protein with multiple membrane spanning regions whose functional site is likely to reside in highly conserved intramembranous and cytoplasmic sequences.

Amino Acid Sequence↗
PubMedDate not supplied

The seizures induced by pilocarpine: behavioral, electroencephalographic and neuropathological studies in rodents.

Seizures produced by systemic administration of pilocarpine hydrochloride, a cholinergic muscarinic agonist, in rodents are proposed as a useful animal model of epilepsy. Pilocarpine-induced seizures in rats and mice are characterized by sequential development of behavioral and electrographic signs, which are followed by widespread damage to the forebrain (hippocampus, amygdala, thalamus, olfactory cortex, neocortex and substantia nigra). Spontaneous seizures may be observed in the long-term period following the administration of convulsant doses of pilocarpine. In experiments designed to examine neuronal networks engaged in the generation and spread of pilocarpine-induced convulsions, a marked role for the basal ganglia is demonstrated. The caudate-putamen, the substantia nigra and the entopeduncular nucleus were found to govern the propagation of seizures produced by pilocarpine. The antiepileptic potential of drugs (diazepam, clonazepam, phenobarbital, valproic acid and trimethadione) against pilocarpine-induced convulsions correlates with their depressant action on the spontaneous activity of non-dopaminergic cells in the substantia nigra. Developmental studies show age-dependent differences in the convulsant response of rats to pilocarpine and status epilepticus are first noted in 2-3 week-old rats, but there is no clear-cut correlation between seizures and evolution of brain damage at this age. The adult pattern of the damage to forebrain is seen after a delay of 1-2 weeks relative to the development of seizures and status epilepticus. The research on the pilocarpine model of convulsions and other cholinergically mediated seizure syndromes may be of value for designing new therapeutic approaches to epilepsy in.

Animals↗