FIG. 6.

Subcellular localization of IMP-1. The subcellular distribution of IMP-1 was characterized immunocytochemically. RD or NIH 3T3 cells were transiently transfected with pCMV-IMP-1. After 48 h, the cells were fixed and incubated with rabbit anti-IMP-1 and stained with fluorescein isothiocyanate-conjugated anti-rabbit IgG. (a to c) Subcellular distribution of IMP-1 in RD cells; (d to f) distribution of IMP-1 in NIH 3T3 cells. (a) In RD cells, staining was observed below the plasma membrane. (b) In clustered groups of cells, IMP-1 was polarized to the free edges of the cells; (c) in myotubes, staining was distributed along the circumference of the complete myotube. (d) In NIH 3T3 cells, staining was evenly distributed in the cytoplasm in clustered cells. (e) In areas with low cell density, staining was observed in the lamellipodia of the leading edge and in the perinuclear region. (f) In completely dispersed cells, IMP-1 was found in discrete foci scattered around the nucleus, below the plasma membrane, and in the lamellipodia. Magnification, ×1,000. Arrows in panels a and d indicate nontransfected cells that served as negative controls for the immunostaining. See Materials and Methods for additional controls.