CELLULAR DETERMINANTS OF THE LATERAL MOBILITY OF NEURAL CELL-ADHESIONMOLECULES

The lateral mobility of the neural cell adhesion molecule (NCAM) was e xamined using fluorescence recovery after photobleaching (FRAP). Vario us isoforms of human NCAM, differing in their ectodomain, their membra ne anchorage mode or in the size of their cytoplasmic domain, were exp ressed in NIH 3T3 cells and C2C12 muscle cells. When the various isofo rms were compared in 3T3 cells, FRAP studies showed both GPI-anchored and transmembrane isoforms diffused rapidly and only small differences in either the diffusion coefficients (D) or the mobile fractions (mf) were measured, suggesting the importance of the ectodomain in regulat ing lateral diffusion. However, the mobility of all NCAM isoforms was greatly reduced in regions of cell-cell contact, presumably due to hem ophilic trans interactions between NCAMs on adjacent cells. NCAM isofo rms transfected into C2C12 cells which express NCAM naturally usually displayed a significantly lower D compared to the same isoforms transf ected into 3T3 cells. Thus, NCAM lateral mobility is modulated in regi ons where cells interact and by the structure of the host cell membran e. (C) 1997 Elsevier Science B.V.