Automated cell tracking identifies mechanically oriented cell divisions during Drosophila axis elongation

Michael F Z Wang,Gang Wang,Miranda Hunter,Christopher M Yip,Rodrigo Fernandez-Gonzalez,Christopher Mcfaul

doi:10.1242/jcs.204453

Abstract

Embryos extend their anterior-posterior (AP) axis in a conserved process known as axis elongation. Drosophila axis elongation occurs in an epithelial monolayer, the germband, and is driven by cell intercalation, cell shape changes, and oriented cell divisions at the posterior germband. Anterior germband cells also divide during axis elongation. We developed image analysis and pattern-recognition methods to track dividing cells from confocal microscopy movies in a generally applicable approach. Mesectoderm cells, forming the ventral midline, divided parallel to the AP axis, while lateral cells displayed a uniform distribution of division orientations. Mesectoderm cells did not intercalate and sustained increased AP strain before cell division. After division, mesectoderm cell density increased along the AP axis, thus relieving strain. We used laser ablation to isolate mesectoderm cells from the influence of other tissues. Uncoupling the mesectoderm from intercalating cells did not affect cell division orientation. Conversely, separating the mesectoderm from the anterior and posterior poles of the embryo resulted in uniformly oriented divisions. Our data suggest that mesectoderm cells align their division angle to reduce strain caused by mechanical forces along the AP axis of the embryo.

Highlights

1 IntroductionThis research project investigates the orientation of cell divisions during axis elongation, a conserved developmental process, and the mechanisms that orient those divisions
To investigate if the divisions of ventral and lateral cells contribute to axis elongation, we used the tools for cell segmentation and division tracking that we developed to quantify cell division orientation
We use laser ablation to investigate the mechanisms that orient ventral cell divisions, and we find that isolating patches of ventral cells from the anterior and posterior ends of the embryo significantly alters the orientation of divisions, suggesting that tissue-wide forces determine cell division orientation during Drosophila axis elongation

Summary

Introduction

This research project investigates the orientation of cell divisions during axis elongation, a conserved developmental process, and the mechanisms that orient those divisions. We used biophysical approaches to investigate the role of mechanical forces in regulating division orientation during axis elongation. Deciphering the mechanisms that orient cell divisions during axis elongation will increase our understanding of developmental defects such as spina bifida and anencephaly. The tools developed in this project can be generally used to identify and measure different cell types, and track their cellular dynamics and tissue morphogenesis automatically. This section includes a description of the axis elongation process and the cellular mechanisms that control axis elongation. The role of mechanical tension orienting cell divisions in other developmental systems, and previous efforts in the development of image analysis tools to detect cells and track their dynamics are discussed

Methods

Results

Discussion

Conclusion