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Light sheet microscopy reveals the cellular mechanisms driving primitive streak formation

Presented by: 
Kees Weijer
Wednesday 16th September 2015 - 11:30 to 12:30
INI Seminar Room 1
Co-authors: Emil Rozbicki (University of Dundee), Manli Chuai (University of Dundee), Antti Karjalainen (University of Dundee), Micheal MacDonald (University of Dundee)      

Gastrulation involves embryo wide tissue reorganizations and deformations driven by coordinated cell shape changes and rearrangements that cannot be imaged using normal microscopic methods. To be able to image the detailed cell behaviors of >200.000 cells we have implemented a scanned light sheet microscope dedicated to imaging large flat samples. This microscope includes dynamics surface tracking method that allows us to keep the embryo in focus of the light sheet during the scanning process. Using this LSM we show that the large scale tissue deformations resulting in the formation the primitive streak in the chick embryo are driven by anisotropic pulling forces generated by cell shape changes and local rearrangements of mesendoderm cells. Cell rearrangements are mediated by sequential, directional contraction of temporary aligned apical junctions in asymmetrically shaped neighboring cells, a process driven by apical acto-myosin II cables that assemble in a Myosin I depen dent manner. The role of Myosin I in the coordination of contraction of junctions in neighboring cells suggests a key role for tension sensing in the assembly and activation of Myosin II cables [1]. We have now implemented an improved method able to track an area of interest, allowing the imaging of cell behaviors at high magnification in tissues undergoing active large scale flows and deformations. This allows study of the detailed cell behaviors during the ingression of mesoderm cells into the primitive streak, a key process in the embryonic development of higher organisms including humans. References [1.] Rozbicki, E., et al., Myosin-II-mediated cell shape changes and cell intercalation contribute to primitive streak formation. Nat Cell Biol, 2015. 17(4): p. 397-408.

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