Loss of Drosophila pseudouridine synthase triggers apoptosis-induced proliferation and promotes cell-nonautonomous EMT

Abstract

Many developing tissues display regenerative capability that allows them to compensate cell loss and preserve tissue homeostasis. Because of their remarkable regenerative capability, Drosophila wing discs are extensively used for the study of regenerative phenomena. We thus used the developing wing to investigate the role played in tissue homeostasis by the evolutionarily conserved eukaryotic H/ACA small nucleolar ribonucleoprotein pseudouridine synthase. Here we show that localized depletion of this enzyme can act as an endogenous stimulus capable of triggering apoptosis-induced proliferation, and that context-dependent effects are elicited in different sub-populations of the silenced cells. In fact, some cells undergo apoptosis, whereas those surrounding the apoptotic foci, although identically depleted, overproliferate. This overproliferation correlates with ectopic induction of the Wg and JAK-STAT (Janus kinase-signal transducer and activator of transcription) mitogenic pathways. Expression of a p35 transgene, which blocks the complete execution of the death program and generates the so-called ‘undead cells', amplifies the proliferative response. Pseudouridine synthase depletion also causes loss of apicobasal polarity, disruption of adherens cell junctions and ectopic induction of JNK (c-Jun N-terminal kinase) and Mmp1 (matrix metalloproteinase-1) activity, leading to a significant epithelial reorganization. Unexpectedly, cell-nonautonomous effects, such as epithelial mesenchymal transition in the contiguous unsilenced squamous epithelium, are also promoted. Collectively, these data point out that cell–cell communication and long-range signaling can take a relevant role in the response to pseudouridine synthase decline. Considering that all the affected pathways are highly conserved throughout evolution, it is plausible that the response to pseudouridine synthase depletion has been widely preserved. On this account, our results can add new light on the still unexplained tumor predisposition that characterizes X-linked dyskeratosis, the human disease caused by reduced pseudouridine synthase activity.

A new role for human dyskerin in vesicular trafficking

“…In fact, perturbation of this traffic widely affects cargo destination and membrane properties, this way potentially altering cell–cell and cell–extracellular matrix interactive communication and related differentiative events. Consistent with these premises, dyskerin depletion may cause both cell‐autonomous and nonautonomous effects, as observed for developmental defects and alterations of long‐range signaling occurring in Drosophila upon in vivo silencing of the DKC1 orthologue . Finally, the endocytic pathway intersects other intracellular transport routes, such as the secretory pathway and the retrograde transport of selected cargo from ERC to the trans‐Golgi network (TGN).…”

“…Similarly, in an X‐DC zebrafish model, changes in telomerase activity were undetectable at early stages, supporting the view that telomerase deficiency is not responsible for the onset of X‐DC pathogenesis . In addition, although Drosophila lacks a canonical telomerase, Drosophila dyskerin is essential for fly viability and its depletion causes a large variety of developmental defects . Finally, snoRNPs have recently gained an important role in several pathologies, including cancer .…”

A functional connection between dyskerin and energy metabolism

“…Although further experiments need to be performed to define the specific molecular pathways stimulated by Iso3 overexpression, it is reasonable to suppose that the protein could have a general impact on snoRNA-mediated processes, including pseudouridylation, thereby concomitantly regulating multiple processes connecting energy metabolism with cell homeostasis. Several considerations support this view: first, snoRNAs are assuming expanding roles in the regulation of cell homeostasis [51] ; second, the mammalian transcriptome is known to be pseudouridylated in a specific manner according to diverse metabolic conditions [52] ; third, Drosophila dyskerin is deeply implicated in the regulation of cell homeostasis in vivo [53] , [54] , [55] .…”

Novel role for Grainy head in the regulation of cytoskeletal and junctional dynamics during epithelial repair

“…Many of these genes belong to the conserved Snail family of transcription factors, such as snail (sna), twist (twi), escargot (esg) and worniu (wor). In addition, the upregulation of Matrix metalloproteinase 1 (Mmp1), an extracellular matrix regulator, and N-Cadherin (CadN), an AJ protein, has also been associated with the EMT phenotype in Drosophila (Oda et al, 1998;Stevens and Page-McCaw, 2012;Vicidomini et al, 2015).…”