Motility disorders and disintegration into separate cells of Trichoplax sp. H2 in the presence of Zn2+ ions and L-cysteine molecules: A systems approach

Placozoa remain an ancient multicellular system with a dynamic body structure where calcium ions carry out a primary role in maintaining the integrity of the entire animal. Zinc ions can compete with calcium ions adsorption. We studied the effect of zinc ions and l-cysteine molecules on the interaction of Trichoplax sp. H2 cells. The regularity of formless motion was diminished in the presence of 20-25 μM of Zn²⁺ ions leading to the formation of branching animal forms. Locomotor ciliated cells moved chaotically and independently of each other leaving the Trichoplax body and opening a network of fiber cells. Application of 100 μM cysteine resulted in dissociation of the plate into separate cells. The combined chemical treatment shifted the effect in a random sample of animals toward disintegration, i.e. initially leading to disorder of collective cell movement and then to total body fragmentation. Two dissociation patterns of Trichoplax plate as "expanding ring" and "bicycle wheel" were revealed. Analysis of the interaction of Ca²⁺ and Zn²⁺ ions with cadherin showed that more than half (54%) of the amino acid residues with which Ca²⁺ and Zn²⁺ ions bind are common. The contact interaction of cells covered by the cadherin molecules is important for the coordinated movements of Trichoplax organism, while zinc ions are capable to break junctions between the cells. The involvement of other players, for example, l-cysteine in the regulation of Ca²⁺-dependent adhesion may be critical leading to the typical dissociation of Trichoplax body like in a calcium-free environment. A hypothesis about the essential role of calcium ions in the emergence of Metazoa ancestor is proposed.