Epithelia are polarized with an apical surface facing the lumen and a basal surface facing the blood. Although apoptotic cells are generally extruded apically into the lumen, we have found other instances where they extrude basally. Since the direction that these cells extrude can have important implications for their fate (especially when apoptosis is blocked), we are investigating what controls the direction of extrusion.
We have recently found that microtubules in the cells neighboring the dying cells target the RhoGEF p115 to the basolateral surface, which form and contracts a panel of actin and myosin to contract basally, driving extrusion apically. Disruption of microtubules or loss of p115 results in basal extrusion. Other factors that control extrusion direction that we are also investigating include gap junctions signaling, matrix components, and polarity genes.