Negative Regulation of Schwann Cell Myelin Protein Gene Expression by the Dorsal Root Ganglionic Microenvironment

Abstract

In vivo, the surface glycoprotein Schwann cell myelin protein (SMP) is expressed in the quail peripheral nervous system exclusively by Schwann cells. It is not detectable at any developmental stage either in enteric glia or in ganglionic satellite cells. We demonstrate here that the satellite glial cells of the dorsal root ganglia start to express SMP on their surface when they are dissociated into single cells and cultivated in vitro. Activation of SMP synthesis is a rapid event observed in mass cultures of dorsal root ganglia dissociated cells as soon as 4 h after the onset of the culture. Confocal microscope analysis revealed that satellite cells may acquire the Schwann cell marker when still in close contact with the neuronal soma. Clonal cultures of satellite cells from E8 dorsal root ganglia demonstrated that the progeny of these SMP-negative cells steadily express SMP. This, together with similar results previously obtained with enteric glia, suggests that the SMP-positive phenotype is a constitutive trait of the peripheral glial cell lineage which is inhibited in satellite cells in vivo by the microenvironment prevailing in the peripheral nervous system ganglia.

In early development of the rat mRNA for the major myelin protein P0 is expressed in nonsensory areas of the embryonic inner ear, notochord, enteric nervous system, and olfactory ensheathing cells

“…In contrast, it is interesting to note the persistence of basal P 0 mRNA expression in adult olfactory nerve ensheathing cells, cells that support continuous axonal regeneration throughout life and promote CNS axonal regeneration (Gudino‐Cabrera et al, 2000; Li et al, 1997; Ramon‐Cueto et al, 1998). Another protein, Schwann cell myelin protein, shows a rather similar pattern of regulation in chick although it is first expressed later than P 0 (Cameron‐Curry et al, 1993; Dulac and Le Douarin, 1991).…”

The avian embryo as a model to study the development of the neural crest: a long and still ongoing story

“…The pluripotency of the NCC is accompanied by a high level of plasticity that can be evidenced by two ways: first, in the differentiation choice which, at the population level, was shown to depend on environmental cues (Le Douarin and Teillet, 1974;Le Douarin et al, 1975;Dulac et al, 1988;Dulac and Le Douarin, 1991;Cameron-Curry et al, 1993 andsee Le Douarin, 1982;Le Douarin and Kalcheim, 1999 for reviews); second, by the fact that, once differentiated, certain NC-derived cell types were shown to be able to reverse their cell type to a pluripotent precursor state and even to a different phenotype. This could be demonstrated by the clonal analysis of quail NCC (see Le Douarin and Dupin, 2003 for a review).…”

The regulation of Krox-20 expression reveals important steps in the control of peripheral glial cell development

“…In vitro culture of DRG has been shown to result in the acquisition by satellite cells of Schwann cell characteristics (Cameron-Curry et al, 1993). To examine the possibility that satellite cells could also be induced to express Krox-20 in vitro, we cultured DRG explants from 17.5 dpc wild-type and Krox-20 +/− embryos and examined Krox-20 and Krox-20/lacZ expression respectively (the Krox-20 protein was detected by immunocytochemistry using a rabbit polyclonal antibody raised against a Krox-20 fusion protein (Vesque and Charnay, 1992)).…”

“…DRG explants constitute rich sources of Schwann cells in culture and these may be partly generated from the satellite cells (Wood, 1976). In addition, in the avian PNS, the Schwann cell myelin protein (SMP) gene, which is expressed exclusively by Schwann cells in vivo (Dulac et al, 1988), can be activated in DRG satellite cells in vitro (Cameron-Curry et al, 1993). These data support the idea that different types of glia are derived from a common lineage and differentiate according to microenvironmental influences and that conversion between the alternative cell types is possible when environmental signalling is modified.…”