Genetic disease mechanisms in the demyelinating peripheral neuropathies Charcot-Marie-Tooth disease type 1A (CMTA) and hereditary neuropathy with liability to pressure palsies (HNPP) as well as transgenic animals with altered PMP22 gene dosage revealed that alterations in PMP22 gene expression have profound effects on the development and maintenance of peripheral nerves. Consequently, the regulation of PMP22 is a crucial aspect in understanding the function of this protein in health and disease. In this study, we dissected and analyzed different cis-acting elements in the 5'-flanking region of the Pmp22 gene in vivo. We found two separate elements that contribute to different aspects of Pmp22 expression. The first is located 5' distally to promoter 1 and is involved in gene regulation during late phases of myelination in development ["late myelination Schwann cell-specific element" (LMSE)] and in remyelination after injury. The second element was identified upstream of promoter 2 and guides Pmp22 expression in sensory neurons. These results suggest that multiple distinct signaling pathways regulating Pmp22 expression in myelination as well as in neurons converge on distinct segments of the PMP22 promoter region. The underlying molecular mechanisms are likely to be crucially involved in the maintenance of the integrity of myelinated peripheral nerves.