The LKB1-like Kinase Elm1 Controls Septin Hourglass Assembly and Stability by Regulating Filament Pairing

Septins are conserved GTP-binding proteins that form filamentous structures at cell division sites in eukaryotic cells. These structures include rings and hourglasses that serve as scaffolds for various cellular processes. In budding yeast, septins localize to the bud neck and form an hourglass structure before cytokinesis. This structure is later remodeled into a double ring that interacts with the actomyosin ring. Despite the known roles of septins in cell division and morphogenesis, the mechanisms governing their higher-order assembly remain unclear. Regulation by conserved kinases has been proposed, but the specific pathways are not fully understood. The role of filament pairing in septin organization has not been well characterized. No prior work had resolved how septin filaments are arranged into ordered structures. This gap motivated the investigation into kinase regulation of septin architecture.

The study aimed to identify the mechanisms by which septin filaments are assembled into ordered structures, such as hourglasses, during cell division. The focus was on the role of the LKB1-like kinase Elm1 in regulating septin architecture. The goal was to determine how Elm1 influences filament pairing and stability in budding yeast. The researchers sought to understand how kinase activity affects septin organization at the filament level. This work addresses the lack of knowledge about how conserved kinases control septin assembly. The study also aimed to clarify the role of the septin-binding protein Bni5 in this process. The motivation was to uncover how filament pairing contributes to the formation of higher-order septin structures. The findings could provide insights into the regulation of cell division and morphogenesis.

The researchers used budding yeast as a model system to study septin organization. They performed genetic and biochemical assays to examine the role of Elm1 in septin assembly. Fluorescent tagging of septin proteins allowed visualization of their localization during the cell cycle. Time-lapse microscopy was employed to observe septin structure dynamics in live cells. The team used protein interaction assays to determine how Elm1 interacts with Bni5. They also conducted kinase activity assays to assess Elm1's regulatory role. The study combined genetic manipulation with functional analysis to dissect the molecular mechanisms. The methods provided a comprehensive approach to understanding septin filament regulation.

The study found that Elm1 specifically associates with the septin hourglass during the cell cycle. Elm1 was shown to regulate filament pairing and the stability of the hourglass structure. The daughter half of the hourglass was particularly affected by Elm1 activity. Bni5 was identified as a key substrate of Elm1 in this process. The researchers observed that Elm1 controls the functionality of Bni5 in septin organization. The results indicate that filament pairing is a regulated process during septin assembly. The data suggest that Elm1 acts at the filament level to control hourglass formation. These findings provide new insights into how kinases regulate septin architecture.

The authors concluded that Elm1 regulates septin hourglass assembly and stability by controlling filament pairing. The findings suggest that filament pairing is a highly regulated process during septin remodeling. The study demonstrates that kinase activity influences septin architecture at the filament level. The role of Bni5 as a substrate of Elm1 was confirmed in this context. The results support the idea that conserved kinases play a role in septin organization. The study provides a model for how filament-level regulation contributes to higher-order septin structures. The findings may inform future work on kinase signaling in cell division. The conclusions are based on the observed effects of Elm1 on septin structure and function.