peripherin. The use of a mouse cDNA probe during the in situ hybridization procedure allowed for the localization of the PRPH gene to the E-F region of mouse chromosome 15 and the q12-q13 region of human chromosome 12. The overall structure of the peripherin gene is nine exons separated by eight introns. This configuration is conserved among the three known mammalian species with known coding for peripherin, namely human, rat and mouse. The nucleotide sequences of human and rat exons were 90% identical and produced a predicted protein that differed at only 18 of 475 amino acid residues. Comparison of introns 1 and 2 also yielded high homology of conserved segments. The 5' flanking regions and regulatory sequences were also very similar and a nerve growth factor negative regulatory element, a Hox protein (See Hox gene) binding site, and a heat shock element were found in all known peripherin genes. Regulatory mechanisms Nerve growth factor (NGF) plays the major role in the regulation of peripherin. It is both a transcriptional inducer and post-translational regulator of peripherin expression in PC12 and neuroblastoma cells. The mechanism of NGF-induced activation occurs through 5' flanking elements and intragenic sequences involving the TATA box and other upstream elements as well as depression at a negative element. The specific signals regulating peripherin expression in vivo are unknown. The peripherin gene is transcriptionally activated in both small and large sized sensory neurons of the dorsal root ganglion at about day E10, and mRNA is present in these cells after postnatal day 2 and throughout adulthood. Post transcriptional mechanisms reduce detectable peripherin to only the small sized cells; however, crushing of the peripheral processes in dorsal root ganglion neurons lead to mRNA and detectable peripherin in the large sized cells. The proinflammatory cytokines, interleukin-6 and leukemia inhibitory factor, can also induce peripherin expression through the JAK-STAT signaling pathway. This specific upregulation is linked to neuronal regeneration. Potential role in the pathogenesis of amyotrophic lateral sclerosis Protein and neurofilamentous aggregates are characteristic of patients with amyotrophic lateral sclerosis, a progressive, fatal neurodegenerative disease. Spheroids, specifically, which are protein aggregates of neuronal intermediate filaments, have been found in patients with amyotrophic lateral sclerosis. Peripherin has been found in such spheroids in conjunction with other neurofilaments in other neuronal diseases, thus suggesting that peripherin may play a role in the pathogenesis of amyotrophic lateral sclerosis. Alternative splicing An alternatively spliced mouse