Fig. 1. Characterization of myotubularin antibodies. (A) `Structural epitope' means that the antibodies recognized only the full-length myotubularin but not overlapping fragments. Western blotting and immunocytochemistry results are from transfected cells as detection of endogenous myotubularin was unsuccessful with these two methods. Immunoprecipitation data were obtained for the endogenous myotubularin from muscle cells and are described elsewhere (Laporte et al., 2001b). +, the antibody is working with the corresponding technique; -, no signal has been detected. At least 2D2, 1G1 and R1208 crossreact with mouse myotubularin, while 1G6, 1D10, R929 and R1141 do not. 1C7 does not immunoprecipitate the mouse myotubularin. R1208 crossreacts with MTMR1 while none of these antibodies crossreact with hMTMR2 and hMTMR3 proteins. (B) Example of immunoprecipitant antibodies crossreacting with the endogenous mouse mMTM1 myotubularin. Mouse C2C12 myotube protein extract or buffer (/) were immunoprecipitated (IP) with the listed antibodies and the purified mouse myotubularin was detected by western blot with the 2D2 antibody (1/2000) followed by an anti-Kappa light chain (1/2500). Myotubularin has an estimated molecular weight of 70 kDa compared with size markers. Transfected COS cells with human myotubularin serve as a size control on the left. R1203 is a serum from a different rabbit immunized as for R1208. The dog myotubularin was also immunoprecipitated and detected with the 1G1 and 2D2 monoclonal antibodies respectively (not shown).