Bilateral JNK activation is a hallmark of interface contractility and promotes elimination of aberrant cells

Abstract

Tissue-intrinsic defence mechanisms eliminate aberrant cells from epithelia and thereby maintain the health of developing tissues or adult organisms. 'Interface contractility' comprises one such distinct mechanism that specifically guards against aberrant cells, which undergo inappropriate cell fate and differentiation programs. The cellular mechanisms which facilitate detection and elimination of these aberrant cells are currently unknown. We find that in Drosophila imaginal discs, interface contractility is associated with bilateral JNK activation at the clonal interface of wild type and aberrant cells. Bilateral JNK activation is unique to interface contractility and is not observed in other tissue-intrinsic defence mechanisms, such as cell-cell competition. We find that JNK is activated cell-autonomously by either of the contacting cell types and drives apoptotic elimination of cells at clonal interfaces. Ultimately, JNK interface signalling provides a collective tissue-level mechanism, which ensures elimination of aberrant, misspecified cells that cannot be identified by cell fitness criteria, as in cell-cell competition. Importantly, oncogenic Ras activates interface contractility but evades apoptotic elimination by bilateral JNK activation. Combined, our work establishes bilateral JNK interface signalling and interface apoptosis as a new hallmark of interface contractility, and it highlights how oncogenic mutations evade tumour suppressor function encoded by this tissue-intrinsic surveillance system.

A cell surface code mediates tissue-intrinsic defense against aberrant cells in epithelia

“…The pathway is tightly controlled to regulate proliferation, but also vein cell fate patterning in late larval and pupal wing tissue 49 . We previously reported that Ras V12 -expressing cells elicit interface surveillance in imaginal discs, as evident by enrichment of Actin at clone boundaries, clone smoothening and activation of JNK interface signaling (Fig 7A) 3,50 . Yet, Ras V12 -expressing cells evade elimination by apoptosis because of the potent anti-apoptotic properties conferred by Ras V12expression, thereby allowing these cells to remain in the tissue and form slow-growing tumors 4 .…”