Two RhoGEF isoforms with distinct localisation control furrow position during asymmetric cell division

Cytokinesis ensures proper division of cellular contents during cell division. The process depends on an acto-myosin contractile ring that forms a cleavage furrow. Rho1 GTPase and its activator Pbl are known to play a central role in this process. However, how Rho1 is regulated to maintain furrow ingression and correct positioning remains unclear. Prior research has shown that Rho1 is essential for furrow formation but does not fully explain its spatial control. This gap motivated the investigation of how Pbl isoforms contribute to Rho1 regulation. The study focuses on Drosophila neuroblasts, which undergo asymmetric division. The mechanism of furrow positioning is not well understood in this context. This work aims to clarify how distinct Pbl isoforms influence Rho1 activity during asymmetric division. Understanding this could help explain how cell fate and size are determined during development.

The study aimed to investigate how Rho1 activity is regulated during asymmetric cell division in Drosophila neuroblasts. The researchers sought to determine the roles of two Pbl isoforms in controlling Rho1 localization and function. They hypothesized that distinct Pbl isoforms might regulate Rho1 in different regions of the cell. This could explain how furrow position is maintained during asymmetric division. The study focused on neuroblasts, which divide to produce cells of different sizes and fates. The researchers wanted to clarify how Pbl isoforms influence Rho1 activity and furrow positioning. They also aimed to assess whether these isoforms contribute to the robustness of the division process. Understanding these mechanisms could provide insights into how cell division is controlled in development.

The researchers used Drosophila neuroblasts as a model system for asymmetric cell division. They examined the localization and activity of Rho1 and its activator Pbl during division. The study employed live imaging to track furrow formation and ingression. They used genetic tools to manipulate Pbl isoform expression and observe effects on Rho1. The researchers analyzed the spatial distribution of Pbl isoforms in the cell. They compared the localization of Pbl-A and Pbl-B during division. The study also assessed myosin enrichment on the cell cortex. These methods allowed them to determine how Pbl isoforms influence Rho1 activity and furrow positioning.

The study found that two Pbl isoforms regulate Rho1 activity in distinct ways. Pbl-A localizes to the spindle midzone and furrow region. It focuses Rho1 activity at the furrow to promote efficient ingression. Pbl-B is found throughout the plasma membrane. It broadens Rho1 activity across the cell cortex. This expansion of Rho1 activity is necessary for myosin enrichment on the entire cortex. The enlarged Rho1 zone helps adjust furrow position during division. This ensures correct daughter cell size asymmetry. The findings suggest that distinct Pbl isoforms enhance the robustness of the division process.

The authors propose that two Pbl isoforms regulate Rho1 activity in distinct regions of the cell. Pbl-A promotes focused Rho1 activity at the furrow to support ingression. Pbl-B broadens Rho1 activity across the cortex to adjust furrow position. This dual regulation ensures correct daughter cell size asymmetry. The findings suggest that isoform-specific localization contributes to division robustness. The study highlights how distinct Pbl isoforms work together during asymmetric division. The authors indicate that this mechanism may be conserved in other cell types. The work provides insight into how Rho1 activity is spatially controlled during division.