Apoptotic regulators dispose of the midbody

Apoptotic regulators dispose of the midbody A pathway that clears up the remains of dead cells also removes the debris generated during cell division, Chai et al. report. The midbody is a microtubule-rich structure that connects the two daughter cells at the end of mitosis. When cytokinesis is completed, the midbody is either shed into the ex-tracellular space or retained by one of the daughter cells, potentially infl uencing its developmental fate. Chai et al. found that, in C. elegans, asymmetrically dividing Q neuroblasts discard their midbodies into their surroundings. The Q cell midbodies were subsequently engulfed and degraded by a neighboring epithelial cell called hyp7, which also internalizes the corpses of apoptotic Q cells during development. Mutations in the genes that promote apoptotic cell en-gulfment blocked midbody clearance, indicating that hyp7 cells use the same pathway to internalize Q cell corpses and cytoki-netic midbodies. Indeed, Chai et al. found that, just like apoptotic cells, Q cell midbodies expose phosphatidylserine on their outer surface and that blocking this lipid signal prevented the hyp7 cell from recognizing and engulfi ng the remnants of Q cell divisions. Apoptotic engulfment genes also regulated midbody clearance in other C. elegans cell lineages. But senior author Guangshuo Ou now wants to study the function of the midbodies produced by worm epithelial stem cells, which are specifi cally retained by the daughter cell that remains undifferentiated. Secretor y proteins hail a cab at the TGN V on Blume et al. reveal how a calcium binding protein helps sort secretory cargo at the trans-Golgi network (TGN). After moving through the secretory pathway from the ER to the Golgi apparatus , proteins are sorted at the TGN for delivery to their fi nal destinations. How soluble proteins are selected for secretion outside of the cell is unclear, though the sorting process appears to rely on an ATPase called SPCA1, which pumps calcium ions into the TGN lumen when activated by the actin-severing protein cofi lin. Cells lacking either SPCA1 or co-fi lin exocytose reduced amounts of many secretory proteins while incorrectly secreting other proteins that are normally retained in the Golgi complex or delivered to lysosomes. Von Blume et al. found that a calcium-binding Golgi protein called Cab45 helps regulate calcium levels and protein sorting at the TGN. Calcium import through SPCA1 was required to retain Cab45 in the Golgi lumen, and Cab45, in turn, was required to …