ERK- and JNK-signalling regulate gene networks that stimulate metamorphosis and apoptosis in tail tissues of ascidian tadpoles.

In ascidian tadpoles, metamorphosis is triggered by a polarized wave of apoptosis, via mechanisms that are largely unknown. We demonstrate that the MAP kinases ERK and JNK are both required for the wave of apoptosis and metamorphosis. By employing a gene-profiling-based approach, we identified the network of genes controlled by either ERK or JNK activity that stimulate the onset of apoptosis. This approach identified a gene network involved in hormonal signalling, in innate immunity, in cell-cell communication and in the extracellular matrix. Through gene silencing, we show that Ci-sushi, a cell-cell communication protein controlled by JNK activity, is required for the wave of apoptosis that precedes tail regression. These observations lead us to propose a model of metamorphosis whereby JNK activity in the CNS induces apoptosis in several adjacent tissues that compose the tail by inducing the expression of genes such as Ci-sushi.