1.
Optogenetic Rescue Reveals Spatiotemporal Rules of Germ-Layer Patterning.
Abstract:
Embryonic cells must interpret morphogen signals that vary in both time and space, but the rules by which they decode these dynamics remain unclear. Here we combine optogenetics with human 2D gastruloids to define minimal WNT signaling rules for germ-layer patterning. We block endogenous WNT secretion to create a “blank canvas” and reconstitute signaling using light-gated LRP6. Systematic temporal scans reveal a narrow competence window when the onset and duration of WNT signaling specify mesoderm; this window is shifted by cell density and amplified by BMP priming, whereas identical WNT inputs outside it invert germ-layer order or generate alternative mesodermal subtypes. Using micromirror-based illumination, we restricted WNT activation to a mid-ring during this temporal window; combined with BMP4, this fully restored germ layer domains with boundaries sharper than those generated by ligand stimulation. Thus, precise spatiotemporal control of a single pathway is sufficient to optically rebuild germ-layer architecture and reveals WNT as a temporal morphogen.
2.
Nucleation of the destruction complex on the centrosome accelerates degradation of β-catenin and regulates Wnt signal transmission.
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Lach, RS
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Qiu, C
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Kajbaf, EZ
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Baxter, N
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Han, D
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Wang, A
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Lock, H
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Chirikian, O
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Pruitt, B
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Wilson, MZ
Abstract:
Wnt signal transduction is controlled by the destruction complex (DC), a condensate comprising scaffold proteins and kinases that regulate β-catenin stability. Overexpressed DC scaffolds undergo liquid-liquid phase separation (LLPS), but DC mesoscale organization at endogenous expression levels and its role in β-catenin processing were previously unknown. Here, we find that DC LLPS is nucleated by the centrosome. Through a combination of CRISPR-engineered custom fluorescent tags, finite element simulations, and optogenetic tools that allow for manipulation of DC concentration and multivalency, we find that centrosomal nucleation drives processing of β-catenin by colocalizing DC components to a single reaction crucible. Enriching GSK3β partitioning on the centrosome controls β-catenin processing and prevents Wnt-driven embryonic stem cell differentiation to mesoderm. Our findings demonstrate the role of nucleators in controlling biomolecular condensates and suggest tight integration between Wnt signal transduction and the cell cycle.
