The cytokines SDF-1alpha and -1beta are two alternatively spliced variants of the CXC (alpha) chemokines that are highly conserved among species. SDF-1alpha was shown to function as a B-cell maturation factor, a ligand for the CXCR4 (LESTR/fusin) chemokine receptor, thereby inhibiting replication of T cell-tropic HIV-1 strains and inducing cell death in human neuronal cell lines. In this report the cloning of the rat SDF-1beta cDNA and a new SDF-1 isoform, SDF-1gamma, are presented. Using Northern blot analysis, the expression pattern of both isoforms was studied in different tissues and it is shown that during postnatal development of the central and peripheral nervous system SDF-1beta- and SDF-1gamma-mRNA expression is inversely regulated. Whilst SDF-1beta-mRNA is the predominant isoform in embryonic and early postnatal nerve tissue, SDF-1gamma-mRNA is expressed at higher levels in adulthood. After peripheral nerve lesion a transient increase in SDF-1beta-mRNA expression is observed. As revealed by in situ hybridization, neurons and Schwann cells are the main cellular sources of both SDF-1beta and SDF-1gamma mRNAs in the nervous system. Computer-assisted analysis revealed that both transcripts encode secreted peptides with putative proteolytic cleavage sites which might generate novel neuropeptides.

Nonconservative point mutations of the peripheral myelin protein 22 (PMP22) are associated with Charcot-Marie-Tooth type 1A disease, the most common inherited peripheral neuropathy in humans, and with the Trembler J (TrJ) and Trembler (Tr) alleles in mice. We investigated the intracellular transport of wild-type PMP22 and its TrJ and Tr mutant forms in Schwann cells and in a non-neuronal cell line. In contrast to wild type, mutant proteins were not inserted into the plasma membrane and accumulated in the endoplasmic reticulum and Golgi compartments. Coexpression of each mutant with wild-type PMP22 confirmed the different intracellular distribution of the mutant forms, indicating that neither the TrJ nor Tr protein has a dominantnegative effect on the cellular distribution of wild-type PMP22. Accumulation of PMP22 immunoreactivity in the cell body of myelinating Schwann cells was also observed in nerve biopsies obtained from CMT1A patients carrying the TrJ point mutation. We propose that impaired trafficking of mutated PMP22 affects Schwann cell physiology leading to myelin instability and loss.

The molecular control mechanisms and regulatory molecules involved in nerve repair are not yet well known. Schwann cells have been attributed an important role in peripheral nerve regeneration; therefore, attention has been drawn to regulatory factors expressed by these glial cells. Here, we demonstrate that Mash2, a basic helix-loop-helix (bHLH) transcription factor previously shown to be crucial for placenta development, is expressed by Schwann cells of adult peripheral nerves. We observed that this gene is downregulated after nerve lesion and, using cDNA array hybridization technology, we could demonstrate that Mash2 is a regulator of Krox24, Mob-1, and CXCR4 expression in cultured Schwann cells. In addition, we provide strong evidence that Mash2 is a negative regulator of Schwann cell proliferation. Mash2 represents a first candidate for the missing class B bHLH proteins in peripheral nerves.

We have isolated a 1.476 bp cDNA (NTII11) representing a transcript that is differntially expressed during sciatic nerve development and regeneration in the rat. Nucleotide sequence comparison indicates partial identity with a recently isolated plasmolipin cDNA. However, our clone extends the published sequence by 234 bp at the 5' end and predicts a protein that contains an additional 25 amino acids at th N-terminus. The open reading frame of th NTII11 transcript encodes a 19.4 kDa protein with four putative transmembrane domains. Northern blot analyses revealed a tissue-specific expression was confirmed by in situ hybridization, and cellular localization of plasmolipin mRNA was demonstrated in Schwann cells of the sciatic nerve and in glial cells of myelinated brain structures. The steady-state levels of plasmolipin mRNA were markedly altered (i) during development of sciatic nerve and brain. (ii) after sciatic nerve injury, and (ii) in cured Schwann cells maintained under different conditions of cell growth and arrest. Our data indicate a function of plasmolipin during myelination in the central as well as in the peripheral nervous system.

The proteolipid plasmolipin is member of the expanding group of tetraspan (4TM) myelin proteins. Initially, plasmolipin was isolated from kidney plasma membranes, but subsequent northern blot analysis revealed highest expression in the nervous system. To gain more insight into the functional roles of plasmolipin, we have generated a plasmolipin-specific polyclonal antibody. Immunohistochemical staining confirms our previous observation of glial plasmolipin expression and proves plasmolipin localization in the compact myelin of rat peripheral nerve and myelinated tracts of the CNS. Western blot analysis indicates a strong temporal correlation of plasmolipin expression and (re-) myelination in the PNS and CNS. However, following axotomy plasmolipin expression is also recovered in non-regenerating distal nerve stumps. In addition, we detected plasmolipin expression in distinct neuronal subpopulations of the CNS. The observed asymmetric distribution of plasmolipin in compact myelin, as well as in epithelial cells of kidney and stomach, indicates a polarized cellular localization. Therefore, we purified myelin from the CNS and PNS and demonstrated an enrichement of phosphorylated plasmolipin protein in detergent-insoluble lipid raft fractions, suggesting selective targeting of plasmolipin to the myelin membranes. The present data indicate that the proteolipid plasmolipin is a structural component of apical membranes of polarized cells and provides the basis for further functional analysis.