Capillarity and active cell movement at mesendoderm translocation in the Xenopus gastrula

During Xenopus gastrulation, leading edge mesendoderm (LEM) advances animally as wedge-shaped cell mass over the vegetally moving blastocoel roof (BCR). We show that close contact across the BCR-LEM interface correlates with attenuated net advance of the LEM, which is therefore pulled forward by tip cells while the remaining LEM frequently separates from the BCR. Nevertheless, lamellipodia persist on the detached LEM surface. They attach to adjacent LEM cells and depend on PDGF-A, cell surface fibronectin and cadherin. We argue that active cell motility on the LEM surface prevents adverse capillary effects in the liquid LEM tissue as it moves by being pulled. It counters tissue surface tension effects with oriented cell movement and bulges the LEM surface out to keep it close to the curved BCR without attaching to it. Proximity to the BCR is necessary in turn for the maintenance and orientation of lamellipodia that permit mass cell movement with minimal substratum contact. Together with a similar process in epithelial invagination, vertical telescoping, the cell movement at the LEM surface defines a novel type of cell rearrangement, vertical shearing.

Tuning intercellular adhesion with membrane-anchored oligonucleotides

Adhesive interactions between cells play an integral role in development, differentiation and regeneration. Existing methods for controlling cell–cell cohesion and adhesion by manipulating protein expression are constrained by biological interdependencies, e.g. coupling of cadherins to actomyosin force-feedback mechanisms. We use oligonucleotides conjugated to PEGylated lipid anchors (ssDNAPEGDPPE) to introduce artificial cell–cell adhesion that is largely decoupled from the internal cytoskeleton. We describe cell–cell doublets with a mechanical model based on isotropic, elastic deformation of spheres to estimate the adhesion at the cell–cell interface. Physical manipulation of adhesion by modulating the PEG-lipid to ssDNAPEGDPPE ratio, and conversely treating with actin-depolymerizing cytochalasin D, resulted in decreases and increases in doublet contact area, respectively. Our data are relevant to the ongoing discussion over mechanisms of tissue surface tension and in agreement with models based on opposing cortical and cohesive forces. PEG-lipid modulation of doublet geometries resulted in a well-defined curve indicating continuity, enabling prescriptive calibration for controlling doublet geometry. Our study demonstrates tuning of basic doublet adhesion, laying the foundation for more complex multicellular adhesion control independent of protein expression.

Tuning intercellular cohesion with membrane-anchored oligonucleotides

Cohesive interactions between cells play an integral role in development, differentiation, and regeneration. Existing methods for controlling cell-cell cohesion by manipulating protein expression are constrained by biological interdependencies, e.g. coupling of cadherins to actomyosin force-feedback mechanisms. We use oligonucleotides conjugated to PEGylated lipid anchors (ssDNAPEGDPPE) to introduce artificial cell-cell cohesion that is largely decoupled from the internal cytoskeleton. We describe cell-cell doublets with a mechanical model based on isotropic, elastic deformation of spheres to estimate the cohesion at the cell-cell interface. Physical manipulation of cohesion by modulating PEG-lipid to ssDNAPEGDPPE ratio, and conversely treatment with actin-depolymerizing cytochalsin-D, resulted respectively in decreases and increases in doublet contact area. Our data are relevant to the ongoing discussion over mechanisms of tissue surface tension and in agreement with models based on opposing cortical and cohesive forces. PEG-lipid modulation of doublet geometries resulted in a well-defined curve indicating continuity, enabling prescriptive calibration for controlling doublet geometry. Our study demonstrates tuning of basic doublet cohesion, laying the foundation for more complex multicellular cohesion control independent of protein expression.