RT Journal Article SR Electronic T1 Large, long range tensile forces drive convergence during Xenopus blastopore closure and body axis elongation JF bioRxiv FD Cold Spring Harbor Laboratory SP 126201 DO 10.1101/126201 A1 David R. Shook A1 Eric M. Kasprowicz A1 Lance A. Davidson A1 Ray Keller YR 2017 UL http://biorxiv.org/content/early/2017/04/10/126201.abstract AB Indirect evidence suggests that blastopore closure during gastrulation of anamniotes, including amphibians such as Xenopus laevis, depends on circumblastoporal convergence forces generated by the marginal zone (MZ), but direct evidence is lacking. We show that explanted MZs generate tensile convergence forces up to 1.5 μN during gastrulation and over 4 μN thereafter. These forces are generated by convergent thickening (CT) until the midgastrula and increasingly by convergent extension (CE) thereafter. Explants from ventralized embryos, which lack tissues expressing CE but close their blastopores, produce up to 2 μN of tensile force, showing that CT alone generates forces sufficient to close the blastopore. Uniaxial tensile stress relaxation assays show stiffening of mesodermal and ectodermal tissues around the onset of neurulation, potentially enhancing long-range transmission of convergence forces. These results illuminate the mechanobiology of early vertebrate morphogenic mechanisms, aid interpretation of phenotypes, and give insight into the evolution of blastopore closure mechanisms.