A dynamic coordination of flagellum and cytoplasmic cytoskeleton assembly specifies cell morphogenesis in trypanosomes.

Jack D Sunter,Vladimir Varga,Samuel Dean,Keith Gull

doi:10.1242/jcs.166447

Abstract

Plasma membrane-to-plasma membrane connections are common features of eukaryotic cells, with cytoskeletal frameworks below the respective membranes underpinning these connections. A defining feature of Trypanosoma brucei is the lateral attachment of its single flagellum to the cell body, which is mediated by a cytoskeletal structure called the flagellum attachment zone (FAZ). The FAZ is a key morphogenetic structure. Disruption of FAZ assembly can lead to flagellum detachment and dramatic changes in cell shape. To understand this complex structure, the identity of more of its constituent proteins is required. Here, we have used both proteomics and bioinformatics to identify eight new FAZ proteins. Using inducible expression of FAZ proteins tagged with eYFP we demonstrate that the site of FAZ assembly is close to the flagellar pocket at the proximal end of the FAZ. This contrasts with the flagellum, which is assembled at its distal end; hence, these two interconnected cytoskeletal structures have distinct spatially separated assembly sites. This challenging result has many implications for understanding the process of cell morphogenesis and interpreting mutant phenotypes.

Highlights

Plasma membrane-to-plasma membrane connections are common features of eukaryotic cells – either between different portions of the same cell or in intercellular junctions
The lateral attachment of the flagellum is mediated by the flagellum attachment zone (FAZ), which is a large cytoskeletal structure that has a key role in cell morphogenesis; perturbations of the FAZ
Cells expressing eYFP–FAZ1 were extracted with detergent and isolated flagella with attached FAZs were produced by treatment with CaCl2 (Fig. 1)

Summary

Introduction

Plasma membrane-to-plasma membrane connections are common features of eukaryotic cells – either between different portions of the same cell or in intercellular junctions. Cytoskeletal frameworks below each respective membrane secure these connections. A major question arises as to how the assembly of such frameworks is coordinated in the respective cellular compartments in order to provide a coherent membrane-to-membrane junction. Trypanosomes are single cells with a distinctive form and shape that is inextricably linked to pathogenesis. This shape is defined by an internal sub-pellicular microtubule-based cytoskeleton and a single flagellum that is attached to the cell body for the majority of its length. The lateral attachment of the flagellum is mediated by the flagellum attachment zone (FAZ), which is a large cytoskeletal structure that has a key role in cell morphogenesis; perturbations of the FAZ

Methods

Results

Conclusion