Dynein functions downstream of GPR-1/2 in directing spindle positioning in C. elegans. (A and B) Wild-type (A) or YFP–GPR-1 (B) one-cell stage embryo stained for DHC-1 (shown in red in merge and alone on the right) and GFP (green in merge). On the very right, higher magnifications of the cortical regions (represented by red boxes) shown in A and B highlight the presence of excess DHC-1 at the cell membrane upon YFP–GPR-1 expression (B, compare with A). The corresponding line scan of pixel intensities (in arbitrary units [au]) across these cortical regions is shown for one representative embryo. 10 embryos were scored for each condition. (C–E) Images from time-lapse DIC microscopy of C. elegans embryos from metaphase in the one-cell stage (left), through anaphase in the one-cell stage (middle), and in the early two-cell stage (right), either wild type (C), expressing YFP–GPR-1 (D), or expressing YFP–GPR-1 and subjected to partial dhc-1(RNAi) in addition (E). See also corresponding Video 5. Elapsed time is indicated in minutes and seconds, with t = 0 corresponding to nuclear envelope breakdown. Red discs and white triangles indicate the position of centrosomes during metaphase and the cleavage furrow, respectively. Spindle pole movements were tracked during 1 min, starting 2 min before the onset of cytokinesis, and are represented on the anaphase embryos. Note excess spindle movements in embryo expressing YFP–GPR-1, which are significantly dampened by partial dhc-1(RNAi). 10 embryos of each condition were analyzed.