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The expression of the neuronal type III intermediate filament protein peripherin was studied in E14 spinal cord fragments and E15 dorsal root ganglia 1-30 weeks after their transplantation to the injured cervical spinal cord of the adult rat. In the dorsal root ganglion transplants, the surviving neurons generally appeared as a rather healthy looking population of small strongly immunoreactive cells which are very similar to the small dorsal root ganglion neurons of adult control rats. In the spinal cord transplants, there were only a few peripherin-immunoreactive neurons, morphologically close to the motoneurons or to the preganglionic sympathetic neurons of adult rats. In both types of transplants, peripherin expression of the immunoreactive neurons was apparently correlated with the previously established ability of these transplanted neurons for extensive axonal growth into a co-grafted peripheral nerve.

Peripherin is the main intermediate filament protein in sympathetic neurons. Immunoreactivity to peripherin was studied in mouse adrenal chromaffin cells after 6 days in culture, and compared to immunoreactivity to tyrosine hydroxylase used as a general marker of chromaffin cells in culture. Most of the cells immunoreactive to tyrosine hydroxylase were rounded, with a glandular phenotype and a few of them had processes. The cells reactive to peripherin only constituted a small proportion of the chromaffin cells (2%), and most of them sent out processes. However, not all the cells with processes were reactive for peripherin. These results did not change in the presence of nerve growth factor. The discussion focuses on the significance of the sub-population of cells reactive to peripherin. We suggest that these cells resemble the small granule chromaffin cells, regarded as an intermediate cell type between glandular cells and neurons. The cells that expressed peripherin here are compared to those selected to form the PC 12 clone. The presence of peripherin in only a few of the cells sending out neurite-like processes is discussed in relation to the expression of other neurofilament proteins in developing cells and to the influence of non-chromaffin cells.

In the course of our studies on the messenger RNA of bacteriophage λ, a low molecular weight RNA, l1, synthesized very early after induction of the prophage, has been identified. It has been possible to obtain it in a very pure state through specific hybridization with the light strand of λ DNA. The results of two-dimensional electrophoresis of pancreatic ribonuclease and ribonuclease T1 digests indicate that l1 is a homogeneous species. Some of its properties were investigated to elucidate whether they were most similar to those of transfer RNA, 5 s RNA or messenger RNA. Although its electrophoretic mobility is similar to that of transfer RNA and 5 s RNA, it is definitely more unstable than these species and in this respect rather like messenger RNA. Its function is yet unknown.