Crumbs Affects Protein Dynamics In Anterior Regions Of The Developing Drosophila Embryo

João Firmino,Elisabeth Knust,Jean-Yves Tinevez

doi:10.1371/journal.pone.0058839

Abstract

Maintenance of apico-basal polarity is essential for epithelial integrity and requires particular reinforcement during tissue morphogenesis, when cells are reorganised, undergo shape changes and remodel their junctions. It is well established that epithelial integrity during morphogenetic processes depends on the dynamic exchange of adherens junction components, but our knowledge on the dynamics of other proteins and their dynamics during these processes is still limited. The early Drosophila embryo is an ideal system to study membrane dynamics during morphogenesis. Here, morphogenetic activities differ along the anterior-posterior axis, with the extending germband showing a high degree of epithelial remodelling. We developed a Fluorescence Recovery After Photobleaching (FRAP) assay with a higher temporal resolution, which allowed the distinction between a fast and a slow component of recovery of membrane proteins during the germband extension stage. We show for the first time that the recovery kinetics of a general membrane marker, SpiderGFP, differs in the anterior and posterior parts of the embryo, which correlates well with the different morphogenetic activities of the respective embryonic regions. Interestingly, absence of crumbs, a polarity regulator essential for epithelial integrity in the Drosophila embryo, decreases the fast component of SpiderGFP and of the apical marker Stranded at Second-Venus specifically in the anterior region. We suggest that the defects in kinetics observed in crumbs mutant embryos are the first signs of tissue instability in this region, explaining the earlier breakdown of the head epidermis in comparison to that of the trunk, and that diffusion in the plasma membrane is affected by the absence of Crumbs.

Highlights

Epithelia are characterised by a pronounced apico-basal polarity of their cells with the apical side facing the outside and the baso-lateral side facing neighbouring cells and/or a basal lamina
While tissue elongation in the anterior region mostly depends on cell intercalation [8,12,13], taking place as response to mechanical forces exerted by the invaginating mesoderm [14] and anisotropies in cortical tension [15,16,17], extension of the posterior region substantially relies on cell divisions oriented along the anterior-posterior axis [18]
To better understand protein dynamics during germband extension in the Drosophila embryo, we developed a Fluorescence Recovery After Photobleaching (FRAP) assay with a higher temporal resolution

Summary

Introduction

Epithelia are characterised by a pronounced apico-basal polarity of their cells with the apical side facing the outside and the baso-lateral side facing neighbouring cells and/or a basal lamina. Cell intercalation is the major driving force for tissue and organ elongation and largely depends on convergence and extension movements. It contributes to shaping of embryos and organs and is instrumental for vertebrate axis elongation, tube formation or germband extension in the Drosophila embryo, to mention just a few [1,5,6,7]. While tissue elongation in the anterior region mostly depends on cell intercalation [8,12,13], taking place as response to mechanical forces exerted by the invaginating mesoderm [14] and anisotropies in cortical tension [15,16,17], extension of the posterior region substantially relies on cell divisions oriented along the anterior-posterior axis [18]

Methods

Results

Conclusion