Abstract
ABSTRACTHow force generated by the morphogenesis of one tissue impacts the morphogenesis of other tissues to achieve an elongated embryo axis is not well understood. The notochord runs along the length of the somitic compartment and is flanked on either side by somites. Vacuolating notochord cells undergo a constrained expansion, increasing notochord internal pressure and driving its elongation and stiffening. Therefore, the notochord is appropriately positioned to play a role in mechanically elongating the somitic compartment. We used multi-photon cell ablation to remove specific regions of the zebrafish notochord and quantify the impact on axis elongation. We show that anterior expansion generates a force that displaces notochord cells posteriorly relative to adjacent axial tissues, contributing to the elongation of segmented tissue during post-tailbud stages. Unexpanded cells derived from progenitors at the posterior end of the notochord provide resistance to anterior notochord cell expansion, allowing for stress generation along the anterior-posterior axis. Therefore, notochord cell expansion beginning in the anterior, and addition of cells to the posterior notochord, act as temporally coordinated morphogenetic events that shape the zebrafish embryo anterior-posterior axis.
Highlights
Elongation of the embryo anterior-posterior (AP) axis requires the physical deformation of multiple axial tissues as they undergo morphogenesis (Bénazéraf et al, 2017; Steventon et al, 2016; Xiong et al, 2020)
Studies in Xenopus embryos have identified the circumferentially constrained expansion of cells within the notochord sheath to lead to an increase in notochord stiffness as the embryo develops, making it a candidate for driving the physical deformation of surrounding somitic tissue that may be required for AP axis elongation (Adams et al, 1990; Koehl et al, 2000)
Vacuolating notochord cells expand over time as they draw in fluid, as in Xenopus (Fig.1C) (Ellis et al, 2013), and notochord volume increases as development progresses (Steventon et al, 2016)
Summary
Elongation of the embryo anterior-posterior (AP) axis requires the physical deformation of multiple axial tissues as they undergo morphogenesis (Bénazéraf et al, 2017; Steventon et al, 2016; Xiong et al, 2020). We utilise targeted multi-photon tissue ablation to investigate the physical impact of notochord morphogenesis on the surrounding somitic compartment, and identify the concomitant expansion of notochord cells, and contribution of progenitors to the posterior end of the notochord, as two temporally coordinated morphogenetic events that shape the zebrafish embryo AP axis.
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