The expression of peripherin, an intermediate filament protein, had been shown by biochemical methods to be localized in the neurons of the PNS. Using immunohistochemical methods, we analyzed this expression more extensively during the development of the rat and compared it with that of the low-molecular-mass neurofilament protein (NF-L), which is expressed in every neuron of the CNS and PNS. The immunoreactivity of NF-L is first apparent at the 25-somite stage (about 11 d) in the ventral horn of the spinal medulla and in the posterior part of the rhombencephalon. The immunoreactivity of peripherin appears subsequently, first colocalized with that of NF-L. Both immunoreactivities then spread out along rostral and caudal directions, but whereas the immunoreactivity of NF-L finally becomes noticeable in every part of the nervous system, that of peripherin remains localized to (1) the motoneurons of the ventral horn of the spinal medulla; (2) the autonomic ganglionic and preganglionic neurons; and (3) the sensory neurons. These results demonstrate that, in the neurons that originate from migrating neural crest cells, the immunoreactivities of peripherin and of NF-L become apparent only when they have reached their destination. The results also show that peripherin is expressed more widely than has been previously observed and that this protein occurs in neuronal populations from different lineages (neural tube, neural crest, placodes) with different functions (motoneurons, sensory and autonomic neurons). The common point of these neurons is that they all have axons lying, at least partly, at the outside of the axis constituted by the encephalon and the spinal medulla; this suggests that peripherin might play a role in the recognition of the axonal pathway through the intermediary of membrane proteins.

Intermediate filament proteins of the rat insulinoma RIN5F cell line were characterized. Two-dimensional gel analysis followed by immunostaining of proteins demonstrated that these cells express both peripherin and the low-molecular-mass neurofilament protein (NF-L); this was confirmed for peripherin by immunohistochemistry, peptide analysis and Northern blot. No expression of these proteins could be detected with these same methods either in the adult pancreas or in the tumor at the origin of the cell line, although such expression was apparent on sections of rat pancreas at embryonal day 16. These results were compared to those obtained on the rat pheochromocytoma PC12 cell line: expression in the adrenal medulla of the embryo, no expression either in the adult tissue or in the tumor, but solely in the derived cell line. The expression of neuronal intermediate filament proteins in the rat insulinoma RIN5F cell line is discussed in relation to its similarity in the rat pheochromocytoma PC12 cell line, and its meaning as to the developmental cell lineage; an ectodermal origin is suggested for the pancreatic islet cells.

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The mouse monoclonal antibody ME 101 raised against human peripherin, an intermediate filament protein (IFP) specific to well defined neuronal populations, recognizes all the major classes of vertebrate IFP in immunoblotting assays. Desmin, GFAP, vimentin, peripherin and the lightest neurofilament protein (NF-L) were cleaved into carboxy-and amino-terminal halves by N-chlorosuccinimide at their unique trytophan residue. Whereas the antibody directed against the epitope common to every IFP (intermediate filament antigen or IFA) and located on the carboxy-terminal end of the rod domain recognizes the carboxy-terminal half, the ME 101 antibody, as the present study illustrates, recognizes specifically the amino-terminal half. From the amino acid sequence data of IFP, it is deduced that the cognate epitope is localized on the amino-terminal part of coil la.

Na-G is a putative sodium (or cationic) channel expressed in neurons and glia of the PNS, in restricted neuronal subpopulations of the brain, and in several tissues outside the nervous system, like lung and adrenal medulla. To analyze the mechanisms underlying tissuespecific expression of this channel, we isolated the 5Ј region of the corresponding gene and show that Na-G mRNA transcription proceeds from a single promoter with multiple initiation sites. By transgenic mice studies, we demonstrate that 600 bp containing the Na-G proximal promoter region and the first exon are sufficient to drive the expression of a ␤-galactosidase reporter gene in neurons of both CNS and PNS, whereas expression in Schwann cells depends on more remote DNA elements lying in the region between Ϫ6,500 and Ϫ1,050 bp upstream of the main transcription initiation sites. Crucial elements for lung-specific expression seem to be located in the region between Ϫ1,050 and Ϫ375 bp upstream of the promoter. Using in vivo footprint experiments, we demonstrate that several sites of the Na-G proximal promoter region are bound specifically by nuclear proteins in dorsal root ganglion neurons, as compared with nonexpressing hepatoma cells.

The most abundant cytoskeletal proteins synthesized in mouse endosteal osteoblastic cells were identified employing two-dimensional polyacrylamide gel electrophoresis and immunoblotting. The relative rate of synthesis of the proteins were measured on radioautograms of detergent-soluble and -insoluble lysates of the cells labeled with [3SS]methionine. Doubling initial cell density induced a 10--45% reduction in the de novo synthesis of actin, ~t-actinin, vimentin and B-tubulins with no change in ct-tubulins. Increasing cell density caused a 45% decrease in the polymerized form of actin with no change in the unpolymerized fraction, suggesting a correlation of alteration of the organization and synthesis of proteins.

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