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SUMMARY:Akantsha Jain-Unveiling the choreography of human brain developmen
 t\;Yamini Ravichandran-Topology changes of the regenerating Hydra define a
 ctin nematic defects as mechanical organizers of morphogenesis - Akantsha 
 Jain\,Department of Biosystems Science and Engineering\, ETH Zürich\, Bas
 el\, Switzerland\; Yamini Ravichandran\,University of Geneva\, Switzerland
DTSTART:20250210T143000Z
DTEND:20250210T153000Z
UID:TALK225505@talks.cam.ac.uk
CONTACT:Jia CHEN
DESCRIPTION:Akantsha Jain's talk title: Unveiling the choreography of huma
 n brain development-Longterm lightsheet imaging unveils morphodynamics in 
 human brain organoids.\n\nAbstract:\nBrain organoids enable mechanistic 
 study of human brain development and provide opportunities to explore self
 -organization in unconstrained developmental systems. We have established 
 long-term light sheet microscopy on unguided multi-mosaic neural organoids
  (MMOs) generated from fluorescently labeled human induced pluripotent ste
 m cells (iPSCs)\, which enables tracking of tissue morphology\, cell behav
 iors\, and subcellular features over weeks of organoid development. We d
 emultiplex multi-mosaic neural organoids using morphometrics to provide
  quantitative measurements of tissue and cellular dynamics\, using Act
 in\, Tubulin\, plasma membrane\, nuclei\, and Lamin labels\, and sho
 w that the organoids exhibit tissue state transitions through neur
 al induction\, lumenization\, and regionalization. We find that desp
 ite morphological heterogeneity\, different organoids exhibit lumen format
 ion and expansion at a consistent time\, coinciding with early neurectoder
 m switching to late neurectoderm fate. This morphological tissue transitio
 n coincides with a switch in underlying gene regulatory networks (GRNs) 
 involving extracellular matrix (ECM) pathway regulators. Presence of a b
 asement membrane rich external ECM promotes cell polarization\, cell align
 ment to form a neuroepithelium\, lumen expansion and leads to formation of
  telencephalic progenitors. However\, in absence of external ECM\, the tis
 sue transition switch is perturbed forming a heterogenous neuroepithelium 
 with mixed cellular alignment and polarity. This promotes formation of inc
 reased neural crest cells and non-telencephalic progenitors. Finally\, we 
 show ECM induced patterning guidance is linked to modulations of t
 he WNT and HIPPO signaling pathway\, including spatially restricted induct
 ion of WLS and YAP1. Altogether\, our work provides a new inroad int
 o studying human brain morphodynamics\, and supports a view that mechanose
 nsing dynamics play a central role in constraining brain regionalization. 
 \n\n\nYamini Ravichandran's talk title: Topology changes of the regenerati
 ng Hydra define actin nematic defects as mechanical organizers of morphoge
 nesis.\n\nAbstract:\nHydra is named after the mythological animal for its 
 regenerative capabilities\, but contrary to its mythological counterpart\,
  it only regenerates one head when cut. Here we show that soft compression
  of head regenerating tissues induces the regeneration of viable\, two hea
 ded animals. Topological defects in the supracellular nematic organization
  of actin were previously correlated with the new head regeneration site1.
  Soft compression creates new topological defects associated with addition
 al heads. To test the necessity of topological defects in head regeneratio
 n\, we changed the topology of the tissue. By compressing the head regener
 ating tissues along their body axis\, topological defects of the foot and 
 of the regenerating head fused together\, forming a toroid with no defects
 . Perfectly ordered toroids did not regenerate over eight days and eventua
 lly disintegrated. Spheroids made from excised body column tissue partiall
 y lose their actin order during regeneration. Compression of spheroids gen
 erated toroids with actin defects. These tissues regenerated into toroidal
  animals with functional head and foot\, and a bifurcated body. Our result
 s show that topological defects in the actin order are necessary to shape 
 the head of the regenerating Hydra\, supporting the notion that actin topo
 logical defects are mechanical organizers of morphogenesis. 
LOCATION:Online
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