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Elife January 1, 2018; 7

Large, long range tensile forces drive convergence during Xenopus blastopore closure and body axis elongation.

Shook DR , Kasprowicz EM , Davidson LA , Keller R .

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.

PubMed ID: 29533180
PMC ID: PMC5896886
Article link: Elife
Grant support: [+]

Species referenced: Xenopus laevis
Genes referenced: fn1 mapt mib1 pnma2 trim9
Antibodies: Notochord Ab1 Somite Ab3

Article Images: [+] show captions
References [+] :
Adams, The mechanics of notochord elongation, straightening and stiffening in the embryo of Xenopus laevis. 1991, Pubmed, Xenbase