PIP2 hydrolysis and calcium release are required for cytokinesis in Drosophila spermatocytes

The role of calcium (Ca2+) in cytokinesis is controversial [1, 2], and the precise pathways that lead to its release during cleavage are not well understood. Ca2+ is released from intracellular stores by binding of inositol trisphosphate (IP3) to the IP3 receptor (IP3R) [3], yet no clear role in cytokinesis has been established for the precursor of IP3, phosphatidylinositol 4,5-bisphosphate (PIP2). Here, using transgenic flies expressing PLC delta-PH-GFP, which specifically binds PIP2 [4-6], we identify PIP2 in the plasma membrane and cleavage furrows of dividing Drosophila melanogaster spermatocytes, and we establish that this phospholipid is required for continued ingression but not for initiation of cytokinesis. In addition, by inhibiting phospholipase C, we show that PIP2 must be hydrolyzed to maintain cleavage furrow stability. Using an IP3R antagonist and a Ca2+ chelator to examine the roles of IP3R and Ca2+ in cytokinesis, we demonstrate that both of these factors are required for cleavage furrow stability, although Ca2+ is dispensable for cleavage plane specification and initiation of furrowing. Strikingly, providing cells with Ca2+ obviates the need to hydrolyze PIP2. Thus, PIP2, PIP2 hydrolysis, and Ca2+ are required for the normal progression of cytokinesis in these cells.