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SUMMARY:Regulation of form in multicellular choanoflagellates and the evol
 utionary cell biology of morphogenesis - Ben Larson (UC San Francisco)
DTSTART:20200122T130000Z
DTEND:20200122T140000Z
UID:TALK138607@talks.cam.ac.uk
CONTACT:George Fortune
DESCRIPTION:Choanoflagellates\, the closest living relatives of animals\, 
 can form multicellular colonies of various shapes and sizes. This diversit
 y and the simplicity of multicellular forms in conjunction with their impo
 rtant phylogenetic position makes choanoflagellates an ideal system for st
 udying the evolution of morphogenesis. Comparisons between the biology of 
 choanoflagellates and animals has begun to shed light on animal origins. H
 owever\, because most work has focused on genetics and genomics\, little i
 s known about the cellular and biophysical mechanisms underlying the regul
 ation of multicellular form in choanoflagellates. Through the quantitative
  characterization of the biophysical processes underlying the development 
 of rosette colonies in the choanoflagellate Salpingoeca rosetta\, we found
  that rosettes reproducibly transition from 2D-3D growth\, despite the und
 erlying stochasticity of the cell lineages. We postulated that the extrace
 llular matrix (ECM) exerts a physical constraint on the packing of prolife
 rating cells\, thereby sculpting morphogenesis. Perturbative experiments c
 oupled with biophysical simulations demonstrated the fundamental importanc
 e of a basally-secreted ECM for rosette morphogenesis. In addition\, this 
 yielded a morphospace for the shapes of multicellular colonies\, consisten
 t with observations across a range of choanoflagellates. Overall\, our bio
 physical perspective complements previous genetic perspectives and thus he
 lps illuminate the interplay between cell biology and physics in regulatin
 g morphogenesis. Another choanoflagellate\, the recently discovered Choano
 eca flexa\, forms multicellular cup-shaped colonies. Colonies rapidly inve
 rt their curvature in response to changing light levels\, which they detec
 t through a rhodopsin-cGMP pathway. Inversion is mediated by cell shape ch
 anges requiring actomyosin-mediated apical contractility and allows altern
 ation between feeding and swimming behavior. C. flexa thus rapidly convert
 s sensory inputs directly into multicellular contractions. In this respect
 \, it may inform reconstructions of hypothesized animal ancestors that exi
 sted before the evolution of specialized sensory and contractile cells.
LOCATION:MR12\, Centre for Mathematical Sciences\, Wilberforce Road\, Camb
 ridge
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