Fig. 2. Formation of large aggregates consisting of PCM-1 deletion mutants. (A) Xenopus A6 cells were transfected with cDNA encoding a GFP fusion protein with a truncated XPCM-1 mutant (aa 745-1273; C). Transfectants expressing small or large amounts of the GFP fusion protein were double stained with anti-XPCM-1 pAb (red) and DAPI (blue). This pAb recognized endogenous XPCM-1 but not the exogenously expressed XPCM-1 mutant. Notice that the GFP-positive large aggregates were formed when the exogenous protein was overexpressed, and that these aggregates recruited endogenous XPCM-1. Bar, 10 µm. (B) Ultrathin section electron microscopy. A6 transfectants overexpressing a GFP fusion protein with a truncated XPCM-1 mutant (aa 745-1273) bore large aggregates, homogenous electron-dense structures (asterisk) (a). Notice that the nucleus, but not these granules, were delineated by membranes (inset). Cells were treated with Triton X-100 and labeled with anti-GFP pAb (b). The surface of the large aggregate (asterisk) was specifically labeled with gold particles (inset). N, nucleus. Bars, (a,b) 500 nm; (inset) 200 nm. (C) The ability of the formation of large aggregates for various deletion mutants of XPCM-1. The constructs represented in color, but not those in black and white, formed large aggregates when overexpressed.