Cap-n-Collar Promotes Tissue Regeneration by Regulating ROS and JNK Signaling in the Drosophila melanogaster Wing Imaginal Disc

Abstract

Regeneration is a complex process that requires an organism to recognize and repair tissue damage, as well as grow and pattern new tissue. Here, we describe a genetic screen to identify novel regulators of regeneration. We ablated the larval wing primordium by inducing apoptosis in a spatially and temporally controlled manner and allowed the tissue to regenerate and repattern. To identify genes that regulate regeneration, we carried out a dominant-modifier screen by assessing the amount and quality of regeneration in adult wings heterozygous for isogenic deficiencies. We have identified 31 regions on the right arm of the third chromosome that modify the regenerative response. Interestingly, we observed several distinct phenotypes: mutants that regenerated poorly, mutants that regenerated faster or better than wild-type, and mutants that regenerated imperfectly and had patterning defects. We mapped one deficiency region to (), the Nrf2 ortholog, which is required for regeneration. Cnc regulates reactive oxygen species levels in the regenerating epithelium, and affects c-Jun N-terminal protein kinase (JNK) signaling, growth, debris localization, and pupariation timing. Here, we present the results of our screen and propose a model wherein Cnc regulates regeneration by maintaining an optimal level of reactive oxygen species to promote JNK signaling.

Centrosome Loss Triggers a Transcriptional Program to Counter Apoptosis-Induced Oxidative Stress

“…Many of the GST family proteins that we found to be upregulated in acentrosomal cells have also previously been found to be upregulated when KEAP1-Nrf2 signaling is experimentally activated (LOBODA et al 2016). Indeed, the Drosophila Nrf2 homolog, Cap-n-collar (Cnc), was recently proposed to help limit ROS levels in the wing disc following tissue damage induced by Rpr misexpression (BROCK et al 2017). In their model, increased ROS levels activate Cnc, which negatively regulates ROS levels via increased transcription of ROS suppressors.…”

“…High levels of JNK activity initiates apoptosis in tissues like the wing and eye imaginal discs. To help compensate for the loss of cells due to apoptosis, lower levels of JNK in neighboring cells can help drive proliferation in the surviving cells to help maintain total cell numbers and tissue integrity, which is a central component of the regeneration process (RYOO et al 2004;FAN AND BERGMANN 2008;MARTIN et al 2009;PEREZ-GARIJO et al 2009;FOGARTY et al 2016;BROCK et al 2017;KHAN et al 2017). Several recent studies demonstrate the important transcriptional responses occurring in damaged/stressed cells, much of it mediated directly by JNK signaling.…”

“…For example, one key pathway that helps drive the compensatory proliferation response is JAK-STAT signaling, whose activating ligands (the Unpaired (Upd) proteins) are themselves transcriptional targets of JNK signaling (PASTOR-PAREJA et al 2008;BUNKER et al 2015;SANTABARBARA-RUIZ et al 2015). Intriguingly, recent studies also uncovered important effects of cell stress and damage on redox balance in imaginal discs, and suggest important roles for reactive oxygen species (ROS) in mediating the activity of the relevant cell signaling pathways to control processes like cell death and compensatory proliferation (KANDA et al 2011;OHSAWA et al 2012;GAURON et al 2013;HUU et al 2015;SANTABARBARA-RUIZ et al 2015;CLEMENTE-RUIZ et al 2016;FOGARTY et al 2016;BROCK et al 2017;KHAN et al 2017;PEREZ et al 2017). Together these studies have begun to elucidate a regulatory network involving complex cross-talk between traditional signaling pathways and ROS that helps correct for cellular damage and maintain tissue homeostasis.…”

“…genetic manipulations (i.e. misexpression of proapoptotic Hid or Rpr(SANTABARBARA- RUIZ et al 2015;FOGARTY et al 2016;BROCK et al 2017;KHAN et al 2017), in tumorforming genetic models(OHSAWA et al 2012;PEREZ et al 2017), or by physical tissue damage(SANTABARBARA-RUIZ et al 2015). However, trying to fit all the data into a single, simple linear pathway is difficult.…”

A Regeneration Toolkit

“…Planarian species are famous for their ability to regenerate whole animals from virtually any body portions, a process that relies on a population of somatic stem cells called neoblasts (Newmark and Sanchez Alvarado, 2000; Wagner et al, 2011). Insect tissues such as imaginal disc and gut can also regenerate (Brock et al, 2017; Guo et al, 2016; Harris et al, 2016; Katsuyama et al, 2015; Martin et al, 2017; Micchelli and Perrimon, 2006; Ohlstein and Spradling, 2006). Among vertebrates, salamanders and zebrafish are capable of regenerating limbs, fins, spinal cord, heart, brain, and other tissues lost or damaged by extreme injury (Becker et al, 1997; Diep et al, 2011; Kyritsis et al, 2012; Pisharath et al, 2007; Poss et al, 2002b; Vihtelic and Hyde, 2000).…”