Fig. 6. A novel low molecular weight, lipid raft-associated isoform of FGFR2 is present in OLs and myelin but not in astrocytes.

Myelin from control and Fgfr2 ^-/- mice was analyzed by 2D (A) and 1D (B) PAGE and immunolabeled with anti-FGFR2. A 52-kd protein was detected in controls, but not in Fgfr2 ^-/- myelin, showing that this is a form of FGFR2. (C) OL or astrocyte lysates immunoblotted with anti-FGFR2 show that the 52-kd band also is present in OLs but not in astrocytes. (D) OL or myelin extracted with 1% TX-100 at 4°C, separated into soluble (S) and insoluble (P) fractions or further fractionated into 10 fractions by sucrose gradient centrifugation, were immunoblotted with anti-FGFR2. A subfraction of the 52-kd isoform of FGFR2 partitions into the pellet fraction and floats in fractions 3-5 of the gradient, showing its lipid raft association. (E) Myelin or OLs, immunoblotted with antibodies that recognize either intracellular (CT) or extracellular (NT) domains of FGFR2, show that the 52-kd protein is recognized only by the CT-specific anti-FGFR2. (F) Northern blot analysis of total RNA from OLs (20 ug/lane) with a specific probe for FGFR2 identified the expected 4.4-kb transcript and a second novel transcript of ~1 kb, a likely message for the 52-kd FGFR2 isoform. Blots reprobed for GADPH show that the RNA was not degraded.