Meike Stumpp and Matthias Leippe

Digestive function, gastric pH, and their role in metazoan evolution

The placozoan Trichoplax adhaerens is currently regarded as one of the most simple, multicellular organisms in the world. The name is derived from its ciliated appearance and means “sticky hairy plate”. One of the most interesting features of this organism is its feeding behavior. When feeding, T. adhaerens glides above food particles and forms an extracellular digestive space between the substrate and its body. For the evolution of multicellular organisms, feeding and extracellular digestion were of upmost importance. Only extracellular digestion made it possible for animals to generate the amount of energy needed to grow bigger and to form special cell types and more advanced tissues leading to the complex organisms, we know today. The “placula theory” for metazoan evolution formulated by Bütschli in 1884, that is still discussed today, is based on the feeding behavior of T. adhaerens. Despite the common ground that extracellular digestion played a vital role in metazoan evolution, the traits leading to successful digestion, such as enzyme characteristics and extracellular acid-base regulation within the digestive space, and how the environment influences these parameters, are not well understood in this old model organism. The project will therefore combine traditional zoology and physiology with modern genetics to study the following three objectives:

Characterization of the abiotic conditions in the digestive space and identification of acid/base transporters involved in ion homeostasis
Identification of digestive enzymes and nutrient transporters
Identification of the environmental impact (ocean acidification) on T. adhaerens using perturbation experiments.

These objectives will be addressed using a variety of techniques including protein biochemistry (enzyme activity assays, immunocytochemistry), electrophysiological approaches (SIET - selective ion electrode technique), and modern genetics (gene-knock down using the morpholino approach or RNAi, in situ hybridization, transcriptomics).