Charles F. Eldridge

Studies of the Initiation of Myelination by Schwann Cells

The rapid morphologic changes in Schwann cells and in their relationships to axons during the transition from the premyelinating to the myelinating state have been known for more than 15 years. The sorting of axons by dividing Schwann cells, the establishment of a 1:1 relationship between a postmitotic Schwann cell, and the onset of myelin sheath formation have all been described in detail. However, the chain of molecular events and mechanisms by which these morphologic changes are regulated has not been elucidated. In this chapter we have reviewed results that strongly suggest that the adhesion molecule L1 is one of the important determinants that mediate the elongation of the Schwann cell along the axon, and the extension of Schwann processes to engulf axons. Thus, L1 functions to promote the spreading of the Schwann cell process over the surface of the axon. L1 does not appear to be exclusively involved in the adhesion of Schwann cells to axons, in the activation of Schwann cell proliferation by axons, or in the induction of synthesis of extracellular matrix proteins. The results from the anti-L1 blocking experiments further provided clues for an understanding of how the expression of GalC and MAG, which are both likely to be involved in the initiation of myelination, are regulated. These results imply that the overall regulation of expression of these early myelin components could require controls other than a single signaling mechanism derived from contact with axons. We propose that the deposition of basal lamina or one of its components could also be involved. Finally, the results from anti-GalC-blocking experiments indicated that GalC is involved in the mechanism of early growth of the myelin spiral.

Basal lamina-associated heparan sulphate proteoglycan in the rat PNS: characterization and localization using monoclonal antibodies.

SummaryCultured rat Schwann cells produce a basal lamina (BL)-associated heparan sulphate proteoglycan (HSPG). The HSPG has an apparent molecular weight of >450 kD, is sensitive to both heparinase and heparitinase and contains a core protein of ∼400kD. Two independently derived monoclonal antibodies, B3 and C17, recognize this HSPG. Using B3 and C17, we found that this HSPG, or immunologically related material, is present in BLs throughout the body and in a small number of connective tissue sites without a formed BL. In the PNS it is present in BLs of Schwann cell-axon units, in synaptic and extrasynaptic portions of muscle fibre BL, and in the BLs of satellite cells that ensheath neurons in sympathetic and sensory ganglia. This HSPG is not detectable in the neuropil of the brain and spinal cord. Neurons, Schwann cells and fibroblasts cultured alone do not assemble a BL or accumulate immunocytochemically detectable amounts of this HSPG, but it is present in BLs assembled in myotube and in Schwann cell-neuron cultures. Thus, this HSPG is a component of most, if not all, BLs in the PNS.

Effects of cis-4-hydroxy-l-proline, an inhibitor of Schwann cell differentiation, on the secretion of collagenous and noncollagenous proteins by Schwann cells

The proline analog cis-4-hydroxy-L-proline (CHP) was previously shown to inhibit both Schwann cell (SC) differentiation and extracellular matrix (ECM) formation in cultures of rat SCs and dorsal root ganglion neurons. We confirmed that CHP inhibits basal lamina formation by immunofluorescence with antibodies to laminin, type IV collagen, and heparan sulfate proteoglycan. In order to test the hypothesis that CHP inhibits SC differentiation by specifically inhibiting the secretion of collagen, cultures grown in the presence or absence of CHP were metabolically labeled with [3H]leucine and the media were analyzed for relative amounts of (a) collagenous and noncollagenous proteins by assay with bacterial collagenase and by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), or (b) triple-helical collagen by pepsin digestion followed by SDS-PAGE. The results indicate that although CHP inhibited the accumulation of secreted collagen in the culture medium and disrupted collagen triple-helix formation, it also significantly inhibited the accumulation of secreted noncollagenous proteins in the medium. CHP had no significant effect on either total protein synthesis (medium plus cell layer) or cell number. We conclude that CHP does not act as a specific inhibitor of collagen secretion in this system, and thus data from these experiments cannot be used to relate SC collagen production to other aspects of SC differentiation. We discuss the evidence for and against specificity of CHP action in other systems.

Essentials of Pediatric Emergency Medicine Fellowship: Part 4: Beyond Clinical Education.

This article is the third in a 7-part series that aims to comprehensively describe the current state and future directions of pediatric emergency medicine fellowship training from the essential requirements to considerations for successfully administering and managing a program to the careers that may be anticipated upon program completion. This article focuses on the skills beyond clinical training required of pediatric emergency medicine physicians including teaching, leadership, teamwork, and communication.

Essentials of PEM Fellowship Part 2: The Profession in Entrustable Professional Activities

Abstract This article is the second in a 7-part series that aims to comprehensively describe the current state and future directions of pediatric emergency medicine (PEM) fellowship training from the essential requirements to considerations for successfully administering and managing a program to the careers that may be anticipated upon program completion. This article describes the development of PEM entrustable professional activities (EPAs) and the relationship of these EPAs with existing taxonomies of assessment and learning within PEM fellowship. It summarizes the field in concepts that can be taught and assessed, packaging the PEM subspecialty into EPAs.

Cells of the Peripheral Nervous System; Requirements for Expression of Function in Tissue Culture

Utilizing mixtures of cell types, complex media, and a collagen substratum, it is possible to obtain a remarkable degree of functional expression in nerve tissue in culture, including myelination, synaptogenesis and histotypic organization (for review see Bunge, 1975; Crain, 1976 and Fischbach and Nelson, 1977). In order to gain an understanding of the contribution of individual cell types to specific functions, and to delineate the precise nutritional and environmental requirements for these functions, it is necessary to define media and substratum components and to study pure cell populations. Furthermore, because certain cell functions are only observed when cell types are cocultured, it is necessary to study cell types when separated and after recombination. In this chapter we briefly describe recent experience with this approach to the study of autonomic and sensory neurons, and of Schwann cells, in the peripheral nervous system. The chapter is primarily a review of work from our laboratory; space does not allow a general review.