Abstract
Background Trichoplax adhaerens is a fascinating early-diverging animal that lacks a nervous system and synapses, and yet is capable of directed motile feeding behavior culminating in the external digestion of microorganisms by secreted hydrolytic enzymes. The mechanisms by which Trichoplax cells communicate with each other to coordinate their activity and behavior is unclear, though recent studies have suggested that secreted regulatory peptides might be involved.Results Here, we generated a high quality mRNA transcriptome of Trichoplax adhaerens , and predicted secreted proteins to identify gene homologues for digestion, development, immunity, cell adhesion, and peptide signaling. Detailed annotation of the expressed Trichoplax gene set also identified a nearly complete set of electrogenic genes involved in fast neural signalling, plus a set of 665 G-protein coupled receptors that in the nervous system integrate with fast signalling machinery to modulate cellular excitability. Furthermore, Trichoplax expresses an array of genes involved in intracellular signaling, including the key effector enzymes protein kinases A and C that functionally link fast and slow cellular signaling. Also identified were nearly complete sets of pre- and post-synaptic scaffolding genes, most encoding appropriate protein domain architectures. Notably, the Trichoplax proteome was found to bear slightly reduced counts of synaptic protein interaction domains such as PDZ, SH3 and C2 compared to other animals, but abundance of these domains did not appear to predict the presence of synapses in early-diverging groups.Conclusions Despite its apparent cellular and morphological simplicity, Trichoplax expresses a rich set of genes involved in complex animal traits. The transcriptome presented here adds a valuable additional resource for molecular studies on Trichoplax genes, exemplified by our ability to clone cDNAs for nine full-length acid sensing ion channel proteins with almost perfect matches with their corresponding transcriptome sequences.
A HISTOCHEMICAL STUDY OF HYDROLYTIC ENZYMES IN MUSCLE FIBERS OF VARIOUS ANIMALS