May 3, 2019

Toby Andrews

10.30-10.45 Toby Andrews

‘How to build a chordate: body plan morphogenesis in the cephalochordate amphioxus’

Embryonic axial elongation is a critical process for establishing the tissue diversity and pattern of the chordate body plan. This involves parallel extension of a notochord and neural tube, and sequential segmentation of paraxial mesoderm to form somites. In this project, we aim to dissect body plan evolution by reconstructing its morphogenesis in the first chordate, taking advantage of a laboratory proxy – the cephalochordate amphioxus. To this end, have performed a multi-scale quantification of axial morphogenesis in the amphioxus, using a novel image acquisition and computational analysis pipeline to construct three-dimensional virtual models of embryos at successive stages of axial development. These contain detailed quantitative information on changes in the size, shape and cellular organisation of axial tissues, that we have used to both describe and model the elongation process. This has revealed elongation to occur in an entirely growth-free system, through synchronous multi-tissue convergent extension of tissue volume established by the end of gastrulation. Surprisingly, we additionally demonstrate, using in silico approaches and in vivo perturbations, that this tissue reorganisation depends on reductive cell division in posterior axial progenitors, which focally elevates tissue fluidity. This ongoing work is revealing the cellular basis of amphioxus morphogenesis for the first time, and implicates axial progenitors as critical agents in body plan innovation.