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2011_Questions_Week_14_Answers

2011_Questions_Week_14_Answers - 1 What happens when you...

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1. What happens when you deplete beta catenin in planarians? -The organism is no longer able to form a posterior side when it is injured. Instead, it forms an anterior side. When an embryo is cut into segments lacking the head or tail, this results in the formation of planarians containing an anterior and posterior head (the Janus phenotype). 2. Could you rescue this by adding/administering Wnt ligands? -No, Beta-catenin is the downstream transcriptional effector of the Wnt ligand. Administering Wnt will have no effect if there is no Beta-catenin. Indeed, there are lots of Wnt ligands in planarians. 3. You want to know which cell types in a planaria require beta-catenin for post-injury axial determination. Specifically, is beta-catenin required in neoblasts, non-neoblasts, or all planarian cells? To address this, you take advantage of the fact that irradiating planarians kills all neoblasts (resulting in a failure to regenerate and ultimately the death of the animal), and that such organisms can be rescued by implanting purified neoblasts from a donor (that was not irradiated). You perform the following experiments on hosts that are all irradiated and treated with Beta-catenin RNAi, cutting out a middle segment from each experimental set to assay its ability to regenerate. If planarians were to specifically required beta-catenin in neoblasts for posterior determination, fill out the predicted phenotypes for these experiments (remember that all hosts above are treated with beta-catenin RNAi). Neoblast Donor Host Treatment Predicted Phenotype Beta catenin RNAi Irradiated Negative control RNAi Irradiated -If it were required in neoblasts, then the following experiment would be observed. Note that the negative control experiment should give you normal regeneration regardless of the mechanism.
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2011_Questions_Week_14_Answers - 1 What happens when you...

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