Posterior axis elongation is a crucial process during metazoan development. In principle, axial extension can be driven either by tissue growth or by tissue rearrangement – or by a combination of the two. In vertebrates, studies based primarily on chick and mouse have suggested that the presence of a posterior proliferative zone is key for driving axial elongation. Here (p. ), Ben Steventon and colleagues assess the relative contribution of volumetric tissue growth versus tissue deformation (lengthening along one axis while narrowing in the other) to posterior body elongation in the zebrafish. During early phases, elongation proceeds without growth and with minimal cell proliferation. At later stages, cell proliferation is confined primarily to the segmented region of the embryo and not to the elongating unsegmented tailbud. Thus, convergent extension-like movements, involving cells entering the posterior trunk from more lateral positions, are the major driving force of elongation in the zebrafish. Through comparative analyses in other vertebrates, the authors’ data suggest a correlation between posterior volumetric growth – as seen in dogfish and mouse but not lamprey or zebrafish – and nutrient availability during embryogenesis.
