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Project 1: Characterizing regeneration enhancer function

The regulation of WNT1 (wg) and WNT6 is the first example we have identified in which a region of the genome responds to damage signals following injury, and then become progressively insensitive to these signals via an epigenetic silencing mechanism.

Enhancer model

Although we have a basic idea of how such a regulatory module might function, we are interested in studying the specifics of this mechanism in the following ways:

  • What factors are required for activation of the enhancer? Although we have identified JNK signaling as an important (and potentially direct) input that activates the enhancer in young discs, it seems that developmental, non-damage induced JNK signals do not. What other factors are necessary for injury-specific activation?
  • How is silencing induced at, and remain localized to, the enhancer? Evidence points to Polycomb group (PcG) proteins being required for full silencing to occur, however the identity of these proteins, as well as other potential silencing regulators, remains unknown. How is this silencing maintained, and can it be reversed? Similarly, the modifications that accumulate and maintain silencing of this enhancer are strictly localized to the few KB surrounding this region, raising the question of why this silencing does not spread further to surrounding DNA – are boundary or barrier elements required to delimit epigenetic silencing?
  • What are the dynamics of silencing? The decline of regeneration gene expression, and indeed the loss of regenerative capacity, is progressive, gradually changing during development. However, epigenetic silencing at a single locus, such as this enhancer, is usually described as more binary – either accessible (active) or inaccessible (silenced). Thus, how does a quantitative change in the activity of a regulatory element lead to a qualitative loss of expression?  To reconcile these contrasting ideas we have developed a “silencing sensor” to understand the dynamics of this silencing mechanism at a single cell resolution.