A threshold level of JNK activates damage-responsive enhancers via JAK/STAT to promote regeneration.

In organisms that can regenerate, thousands of genes are upregulated following damage in order to regenerate missing tissue. Only recently has it been identified how these genes become activated following damage. Damage-Responsive (DR) enhancers are regeneration regulatory regions that recognize damage stimuli and respond by activating genes essential for regeneration. To study DR enhancer activity, our lab uses the wing imaginal disc, which is highly regenerative. Currently, we do not know how DR enhancers become activated following damage. My work focuses on identifying the damage-induced signals that activate DR enhancers to promote regeneration. To study regeneration, damage is caused by a genetic ablation system called DUAL control, consisting of a bipartite gene expression system that induces apoptosis in the disc while simultaneously activating the Gal4/UAS system in the surrounding regenerating cells to knockdown or overexpress any gene of interest. This system has been paired with GFP reporters of DR enhancers to visualize their activity during regeneration.
Using these techniques, it was found that the transcription factor of the JNK signaling pathway is necessary for enhancer activation following damage, but developmental instances of JNK expression is insufficient for enhancer activation. An important question that remains unresolved, is whether a damage-induced factor is needed along with JNK signaling, or is it differences in levels of JNK signaling that is required for enhancer activation. To narrow down potential candidates involved in DR activation, a damage stimulus was initiated while blocking cell death. It was found that DR is capable of being activated independent of cell death. This suggests that the activating factor is likely a direct downstream targets of JNK, one of those being JAK/STAT, which is known to be involved in regeneration. To test if the transcription factor for the JAK/STAT pathway is involved, a new DR transgenic reporter was created lacking the JAK/STAT transcription factor binding sites which reduced enhancer activation. JAK/STAT is not only required for full activation of DR but also controls the spatial domain where DR is expressed. Upon knockdown of the JAK/STAT pathway DR expression is limited to the cell directly adjacent to the wound.
Additionally, I have demonstrated that lower levels of JNK expression seen in a developmental context are insufficient for enhancer activation, and high levels of JNK expression that occur during damage are required for enhancer activation. My work has shown that both damaged-induced factors and levels of JNK signaling are essential for DR activation. Overall, my research aims to identify the minimal components necessary for DR activation, which might be used to activate DR in non-regenerative tissue to permit regeneration.