Characterization of two distinct populations of detergent resistant membrane complexes isolated from chick brain...

We report the isolation of two distinct populations of detergent resistant membrane complexes (DRMCs) from 1-day-old chick brain, utilizing a procedure involving Triton X-100 insolubility and sucrose density gradient centrifugation. The first population is abundant (1.8% of the total homogenate protein), highly enriched for two glycosylphosphatidylinositol (GPI)-anchored proteins (Thy-1 and AvGp50), and not enriched for caveolin. The second population is of relatively low abundance (0.2% of the total homogenate), contains relatively low levels of Thy-1 and AvGp50 enrichment, and is highly enriched in caveolin. Both populations of DRMCs are enriched for cholesterol, ganglioside GM1, total kinase and tyrosine kinase activities, and c-Src and c-Fyn. However, there are differences in the Coomassie-stained protein profiles, phosphoprotein components, tyrosine kinase activity, and electron microscopic morphology when the Thy-1 and AvGp50-enriched DRMCs are compared to the caveolin-rich DRMCs. In addition, the GPI-enriched DRMCs contain CaM kinase type II immunoreactivity, whereas this molecule was undectable in the caveolin-rich DRMCs. The isolation of two distinct DRMC fractions may be representative of unique plasma membrane signaling domains involved in GPI-anchored protein or other receptor-mediated signal transduction within the avian nervous system. Further, we have demonstrated for the first time that nervous system tissue, in particular the hatch chick cerebellum, contains caveolin immunoreactivity.