Feo, the Drosophila homolog of PRC1, is required for central-spindle formation and cytokinesis.

We performed a functional analysis of fascetto (feo), a Drosophila gene that encodes a protein homologous to the Ase1p/PRC1/MAP65 conserved family of microtubule-associated proteins (MAPs). These MAPs are enriched at the spindle midzone in yeast and mammals and at the fragmoplast in plants, and are essential for the organization and function of these microtubule arrays. Here we show that the Feo protein is specifically enriched at the central-spindle midzone and that its depletion either by mutation or by RNAi results in aberrant central spindles. In Feo-depleted cells, late anaphases showed normal overlap of the antiparallel MTs at the cell equator, but telophases displayed thin MT bundles of uniform width instead of robust hourglass-shaped central spindles. These thin central spindles exhibited diffuse localizations of both the Pav and Asp proteins, suggesting that these spindles comprise improperly oriented MTs. Feo-depleted cells also displayed defects in the contractile apparatus that correlated with those in the central spindle; late anaphase cells formed regular contractile structures, but these structures did not constrict during telophase, leading to failures in cytokinesis. The phenotype of Feo-depleted telophases suggests that Feo interacts with the plus ends of central spindle MTs so as to maintain their precise interdigitation during anaphase-telophase MT elongation and antiparallel sliding.