Constitutively active protein required for microtubule and F-actin growth, structural maintenance and organization during excretory cell tubulogenesis. Localizes to leading edge F-actin and microtubules. Expressed in the excretory cell and mostly accumulates at the tip of the excretory cell canals. Defective cytoskeleton organization characterized by disrupted F-actin and microtubule dynamics leading to abnormal excretory cell tubulogenesis. Specifically, F-actin structure and organization in excretory cell canals throughout life is disrupted and microtubule organizing centers accumulate at the tips of excretory cell canals, with a strong reduction along the canals, and the direction of microtubule growth is altered. Belongs to the formin homology family.