The Class I PITP Giotto Is Required for Drosophila Cytokinesis

Abstract

Phosphatidylinositol transfer proteins (PITPs) are highly conserved polypeptides that bind phosphatidylinositol or phosphatidylcholine monomers, facilitating their transfer from one membrane compartment to another . Although PITPs have been implicated in a variety of cellular functions, including lipid-mediated signaling and membrane trafficking, the precise biological roles of most PITPs remain to be elucidated . Here we show for the first time that a class I PITP is involved in cytokinesis. We found that giotto (gio), a Drosophila gene that encodes a class I PITP, serves an essential function required for both mitotic and meiotic cytokinesis. Neuroblasts and spermatocytes from gio mutants both assemble regular actomyosin rings. However, these rings fail to constrict to completion, leading to cytokinesis failures. Moreover, gio mutations cause an abnormal accumulation of Golgi-derived vesicles at the equator of spermatocyte telophases, suggesting that Gio is implicated in membrane-vesicle fusion. Consistent with these results, we found that Gio is enriched at the cleavage furrow, the ER, and the spindle envelope. We propose that Gio mediates transfer of lipid monomers from the ER to the equatorial membrane, causing a specific local enrichment in phosphatidylinositol. This change in membrane composition would ultimately facilitate vesicle fusion, allowing membrane addition to the furrow and/or targeted delivery of proteins required for cytokinesis.

Mutations inCog7affect Golgi structure, meiotic cytokinesis and sperm development duringDrosophilaspermatogenesis

“…In addition to defects in recruitment of membrane trafficking proteins, Cog7 mutant spermatocytes also exhibited incomplete actomyosin ring constriction, as also observed in fws , gio Giansanti et al, 2006), fwd and Rab11 (Giansanti et al, 2007) mutant spermatocytes. Although regular actomyosin rings formed during early telophase, they failed to contract during cytokinesis.…”

“…Loss of function of Drosophila Cog7 affected the integrity and the number of Golgi stacks in primary spermatocytes, as well as the structure of Golgi cisternae, consistent with previous EM studies in COG7 patient cells (Reynders et al, 2009) 2006 ). Loss of function of Cog7, like loss of function of fws, also disrupted assembly or stability of the Golgi-based acroblasts that form after meiosis II from Golgi-derived vesicles in onion-stage spermatids Giansanti et al, 2006;Giansanti et al, 2007).…”

“…Previous studies showed that the phosphatidylinositol transfer protein (PITP) Giotto/Vib (Gio/Vib) and the small GTPase Rab11 concentrate to the cleavage furrow and are both required for spermatocyte cytokinesis (Gatt and Glover, 2006;Giansanti et al, 2006;Giansanti et al, 2007;Polevoy et al, 2009). Rab11, Gio and the Phosphatidylinositol 4-kinase b (PI4Kb) Fwd might function in the same pathway controlling membrane addition to the spermatocyte cleavage site, with Gio and Fwd acting upstream of Rab11 (Giansanti et al, 2007).…”

“…However, loss of Cog7 and the consequent Golgi defects did not substantially affect cytokinesis of neuroblasts. Other mutations in membrane traffic components such as fwd, fws, bru, gio and Arf6 disrupt spermatocyte cytokinesis causing little or no effects on cytokinesis of larval neuroblasts or S2 cells (Brill et al, 2000;Eggert et al, 2004;Farkas et al, 2003;Giansanti et al, 2004;Giansanti et al, 2006;Dyer et al, 2007;Robinett et al, 2009). The large size of spermatocytes and the rapid succession of two meiotic divisions might explain the particular requirement of male meiotic cytokinesis for vesicle trafficking pathways.…”

“…For example, Drosophila spermatocytes are quite large cells (more than 20 mm in diameter), that complete two meiotic divisions in less than two hours (Fuller, 1993;Giansanti et al, 2012). Spermatocyte cytokinesis proved to be sensitive to mutations affecting vesicle traffic components (Brill et al, 2000;Farkas et al, 2003;Dyer et al, 2007;Gatt and Glover, 2006;Giansanti et al, 2006;Giansanti et al, 2007;Polevoy et al, 2009;Robinett et al, 2009;Xu et al, 2002a;Zhou et al, 2011). During Drosophila spermiogenesis, round spermatids, ,12 mm in diameter, undergo drastic morphological changes in cell surface before reaching the impressive 1.8 mm in length of sperm tails (Fuller, 1993;Tates, 1971;Zhou et al, 2011).…”