Title: Reengineering Somite Segmentation without the Vertebrate Segmentation Clock

Speaker: Ertugrul Ozbudak, Northwestern University

Abstract: Somitogenesis establishes the segmental pattern of the vertebral column. A molecular segmentation clock sets the pace of somite formation while a spatial gradient of ERK activity instructs segment boundary positions. However, how cells are primed to form a segment boundary at discrete locations and how the clock and gradient are mechanistically integrated were unclear. We developed transgenic reporters for the segmentation clock and the gradient in zebrafish embryos. We show that the segmentation clock periodically inhibits the gradient, therefore projecting its oscillation onto the gradient. Pulsatile inhibition of the gradient can fully substitute for the role of the clock, and other targets of the clock are dispensable for sequential segmentation. We propose a "Clock-dependent Oscillatory Gradient (COG)" model in which the clock periodically triggers discrete jumps of the positional information. Computational simulations of the COG model explain all experimental observations; the new model effectively replaces a long-standing textbook model.

Zoom: https://northwestern.zoom.us/j/95679444293

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