Hydra head regeneration ruled by Wnt3

CHARA OSVALDO; BRUSCH LUTZ; GALLIOT BRIGITTE; DEUTSCH ANDREAS

Heidelberg

Conferencia; 12th International Conference on Systems Biology, Heidelberg/Mannheim; 2011

We study the head regeneration after decapitation of thefresh water polyp Hydra. The question is how does theremaining tissue measure the degree of injury and trigger aregeneration response of adequate magnitude? We addressthis issue employing a mathematical modelling approachbased on experimental data. The Hydra body column can beviewed as a hollow bilayered tissue cylinder with head andfeet on opposite ends referred to as apical and basal,respectively. The tissue consists of the following cell types:ectodermal and endodermal cells (in the epithelial lineage),interstitial stem cells, progenitors, neurons, nematocytes andgland cells (in the interstitial lineage). Previous experiments ofcutting Hydra into two halves showed secretion of Wnt3molecules by cells undergoing apoptosis near the amputationplane of the basal half.We developed a model based on asystem of coupled partial differential equations which includesthe mentioned cell types, as well as Wnt3 and a putativemolecule denominated proapo. The cell dynamics is modelledinvolving cell differentiation, self-renewal and basal apoptosis(i.e. not triggered by amputation). A set of steady statesolutions were found which fits experimental results of Hydrabefore (or without) amputation. It is assumed that proapo isproduced as a consequence of decapitation which, in turn,triggers the production of Wnt3 by apoptotic cells near theamputation plane. Wnt3 and proapo could diffuse deeper intothe tissue and progressively undergo lytic degradation. In thiswork Wnt3 could influence cell dynamics by two alternativemechanisms: a) through an increases in cell proliferation inresponse to the concentration of Wnt3 or b) cell migrationfollowing the spatial gradient of Wnt3. After the model wasimplemented in a simulation program coded in C++, modeldependentfitting to the experimental data was performed.The obtained results corroborate the multiple roles of Wnt3 inthe regeneration process in Hydra.