600B Poster - 08. Patterning, morphogenesis and organogenesis
Friday April 08, 2:00 PM - 4:00 PM

Authors:
Matthew Lefebvre; Nikolas Claussen; Noah Mitchell; Sebastian Streichan

Affiliation: University Of California Santa Barbara

Keywords:
o. tissue growth and remodeling; r. cell-cell interactions

Morphogenesis is an inherently dynamic process which bridges cellular and tissue scales. Across metazoans, the actomyosin cytoskeleton plays a central role in sculpting morphogenetic geometry. Yet the mechanisms by which it is controlled remain poorly understood. Recent evidence suggests two regulatory principles: instructive genetic programs, and a dynamic response to mechanical stimuli. The two are not mutually exclusive and have proven difficult to disentangle. In \emph{D. melanogaster} body axis elongation, a canonical example of convergent extension, both the required genetic patterning inputs, and the force-generating cytoskeletal actors have been identified. Non-muscle myosin II (MyoII) is recruited to dorso-ventral cell-cell junctions where it generates forces. In anterior-posterior patterning mutants axis elongation is impaired, but the way in which genetic information orients the cytoskeleton remains unclear.
We study this process using live \emph{in-toto} imaging and dynamic, quantitative analysis. A systematic comparison of the genetic patterning system as well as the magnitude and orientation of junctional MyoII reveals a series of discrepancies. Crucially, during the course of axis elongation, gene patterns permanently deform with the flowing tissue, while the MyoII orientation remains aligned to the dorso-ventral axis, with only a temporary deflection. Therefore, we propose that MyoII is recruited by a geometrically defined static source rather than cell-intrinsic genetic patterning. Under this hypothesis, we can explain and quantitatively predict MyoII dynamics.
Our results suggest that genetic patterning does not directly instruct cytoskeletal regulation during axis elongation. Mechanical cues, in particular embryo-scale tension, are a natural candidate for the static source whose signatures we uncover, since they need not behave in the same way as genetic cues in deforming tissue. Our results add a novel perspective on developmental biology: morphogenesis may be organized by tissue geometry without constant input of genetic patterning, allowing for robust, modular and self-organized processes.