MEDIA THAT SUPPORT THE GROWTH AND DIFFERENTIATION OF OLIGODENDROCYTESDO NOT INDUCE OLFACTORY ENSHEATHING CELLS TO EXPRESS A MYELINATING PHENOTYPE

The glial cells that ensheath olfactory axons are referred to as enshe athing cells. In vivo, these non-myelinating glial cells express a mix ture of astrocyte-specific and Schwann cell-specific phenotypic featur es with the former cellular phenotype predominating, but in vitro can assemble a myelin sheath when co-cultured with dorsal root ganglion ne urons. Thus, certain in vitro conditions induce ensheathing cells to e xpress a phenotype more like that of a myelinating Schwann cell. The p resent study addresses whether ensheathing cells will express a myelin ating phenotype in neuron-free cultures when fed for 1 to 5 weeks with media shown to promote the growth and differentiation of oligodendroc yte progenitor cells. The ensheathing cell cultures were initiated usi ng the nerve fiber layers (NFL) of rat olfactory bulb primordia. Oligo dendrocyte cultures were established from newborn rat neopallium and f rom the tissue that remained after removing the NFL from the developin g olfactory bulb (i.e., the OB-NFL). The cultures were double-labelled with rabbit polyclonal antibodies to S100 or glial fibrillary acidic protein in combination,with the mouse monoclonal antibodies 04, BRD1 [ anti-galactocerebroside (anti-GAL-C)], and anti-myelin basic protein ( MBP). In some experiments the ensheathing cells were labelled with PKH 26 prior to being co-cultured with oligodendrocytes of the OB-NFL. Non e of the media induced ensheathing cells to express either GAL-C or MB P. However, when 0.5 mM dibutyrylcyclic-AMP (dBcAMP) was added to the medium, ensheathing cells became GAL-C + ve, but remained MBP-ve. The molecular mechanisms that regulate the expression of a myelinating phe notype by ensheathing cells appear to be different from those that ope rate in oligodendrocytes. (C) 1994 Wiley-Liss, Inc.