Analyzing the functions of Rab11-effector proteins during cell division

Abstract

Recycling endosomes recently have emerged as major regulators of cytokinesis and abscission steps of cell division. Rab11-endosomes in particular were shown to transport proteins to the mitotic ingression furrow and play a key role in establishing the abscission site. Rab11 GTPase functions by binding and activating various effector proteins, such as Rab11 family interacting proteins (FIPs). FIPs appear to be at the core of many Rab11 functions, with FIP3 playing a role in targeting of the Rab11-endosomes during mitosis. Here we summarize the newest finding regarding the roles and regulation of FIP3 and Rab11 complex, as well as describe the methods developed to analyze membrane and cytoskeleton dynamics during abscission step of cytokinesis.

Keywords: Abscission; Cytokinesis; FIP3; Midbody; Mitosis; Rab11; Recycling endosomes.

Figure 1. Mechanisms mediating abscission

In early telophase, as midbody is formed from central spindle microtubules, ESCRT-III complex is recruited to the midbdoy. In late telophase, Rab11/FIP3 and Rab35 endosomes (likely different endosomal populations) are delivered and fuse with cleavage furrow plasma membrane. Among other factors, these organelles deliver OCRL and p50RhoGAP leading to the localized disassembly of actin cytoskeleton and severing of central spindle microtubules. Actin depolymerization induces formation of the secondary ingression and ESCRT-III translocation from the midbody to the abscission site. Delivery of the ESCRT-III to the secondary ingression leads to a final scission event and separation of daughter cells.

Figure 2. Models of asymmetric and symmetric abscission

In many dividing cells abscission sites are established bi-laterally on both sides of the midbody. That leads to a shedding of the midbody to the extracellular space (left panel). However, abscission site can also be formed only on one side of the midbody, leading to asymmetric abscission (right panel). This type of asymmetric abscission results in midbody inheritance by one of the daughter cells.

Figure 3. Rab11/FIP3-endosome dynamics during cytokinesis

During metaphase and anaphase Rab11/FIP3-endosomes associate with centrosomes. As dividing cell progresses to telophase and midbody is formed, Rab11/FIP3-endosomes start translocated along central spindle microtubules to the close proximity of the midbody. My late telophase almost all Rab11/FIP3-endosmes are localize at and around the midbody. This translocation precedes and is required for the final abscission event.

Figure 4. Model depicting the role of midbody-associated AMIS formation and endosome transport during lumenogenesis in epithelial cells

Upon division of non-polarized epithelial cell, apical membrane initiation site (AMIS) forms abound midbody in late telophase. Rab11/FIP3-endosomes containing apical cargo, such as Crumbs3 and gp135, are then delivered along centrals spindle microtubules to the AMIS, where they fuse and form nascent apical lumen. As cells polarized epithelial cells divide these nascent lumens mature to become a function apical lumens.