Meeting Abstract
In the genomic era, we know that the earliest-branching animal phyla include ctenophores, sponges, and cnidarians. Intriguingly, these animals all share bodies that are more amorphous, acellular materials by volume than they are living cells. Ctenophores—perhaps the first-branching extant metazoan taxon—are primarily composed of a voluminous hydrogel called the “mesoglea” that is derived from the extracellular matrix of the thin epithelium that surrounds it. We report here that this gel is far from simple, but has sophisticated material properties. First, it behaves as a non-Newtonian fluid that is also self-healing. It is also molecularly crowded, with a viscous fluid phase and very slow diffusion of sub-micron beads. Paradoxically, while the gel appears “full” to diffusing particles, it looks “empty” to light, with a refractive index almost identical to seawater and vanishingly low concentrations of proteins or sugars. How can a structure be “empty” to light, yet otherwise exhibit these sophisticated properties? Further, what do these material properties teach us about the bodies of the earliest animals? We will present results on the biochemical constituents of ctenophore mesoglea, their spatial organization within the gel, and on the viscoelastic, shear-hardening properties of this enigmatic tissue in the context of the animals’ development and ecophysiology.
