title: Spatiotemporal mechanical variation reveals critical role for rho kinase during primitive streak morphogenesis.
abstract: Large-scale morphogenetic movements during early embryo development are driven by complex changes in biochemical and biophysical factors. Current models for amniote primitive streak morphogenesis and gastrulation take into account numerous genetic pathways but largely ignore the role of mechanical forces. Here, we used atomic force microscopy (AFM) to obtain for the first time precise biomechanical properties of the early avian embryo. Our data reveal that the primitive streak is significantly stiffer than neighboring regions of the epiblast, and that it is stiffer than the pre-primitive streak epiblast. To test our hypothesis that these changes in mechanical properties are due to a localized increase of actomyosin contractility, we inhibited actomyosin contractility via the Rho kinase (ROCK) pathway using the small-molecule inhibitor Y-27632. Our results using several different assays show the following: (1) primitive streak formation was blocked; (2) the time-dependent increase in primitive streak stiffness was abolished; and (3) convergence of epiblast cells to the midline was inhibited. Taken together, our data suggest that actomyosin contractility is necessary for primitive streak morphogenesis, and specifically, ROCK plays a critical role. To better understand the underlying mechanisms of this fundamental process, future models should account for the findings presented in this study.
authors.affiliation: Department of Mechanical Engineering, Georgia Institute of Technology, 315 Ferst Dr. NW, Atlanta, GA 30332, USA.
authors.forename: Julia
authors.initials: J
authors.lastname: Henkels
authors.forename: Jaeho
authors.initials: J
authors.lastname: Oh
authors.forename: Wenwei
authors.initials: W
authors.lastname: Xu
authors.forename: Drew
authors.initials: D
authors.lastname: Owen
authors.forename: Todd
authors.initials: T
authors.lastname: Sulchek
authors.forename: Evan
authors.initials: E
authors.lastname: Zamir
mesh_terms: D000205:Actomyosin / Q000502:physiology; D000577:Amides / Q000494:pharmacology; D000818:Animals; D055119:Elastic Modulus; D004625:Embryo, Nonmammalian; D005855:Germ Layers / Q000196:embryology; D018625:Microscopy, Atomic Force; D009024:Morphogenesis; D054240:Primitive Streak / Q000196:embryology*; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011725:Pyridines / Q000494:pharmacology; D011784:Quail; D054460:rho-Associated Kinases / Q000037:antagonists & inhibitors / Q000502:physiology*
chemical_list: D000577:Amides; D047428:Protein Kinase Inhibitors; D011725:Pyridines; C108830:Y 27632; D000205:Actomyosin; D054460:rho-Associated Kinases