Rab11 acts downstream of fwd to promote completion of cytokinesis. (A) Phase–contrast (phase) and fluorescence images of dividing spermatocytes stained for Rab11 (green), Nuf (red), and DNA (blue). Arrows indicate the midzone. Colocalization of Rab11 and Nuf is yellow (overlay). Endogenous Rab11 and Nuf colocalize at the midzone in wild type (top panels). Neither Rab11 nor Nuf accumulate in the midzone in fwd mutant cells (middle panels). Localization of Rab11 and Nuf is restored upon expression of Rab11Q70L (bottom panels). Bar, 20 µm. (B) Quantification of the number of spermatids resulting from successful cytokinesis versus cytokinesis failure (as in Fig. 2, B and C). A minimum of 300 cells derived from at least 10 males was counted for each genotype. fwd mutant testes (fwd/Df) show a large proportion of cells with 2 or 4 nuclei. Overexpression of activated Rab11Q70L (Q70L#1, Q70L#3), but not wild-type Rab11 (Rab11#1, Rab11#3), partially rescues the fwd cytokinesis defect, producing increased numbers of cells with 1, 2, or 3 nuclei.
