Regenerating tissue must initiate the signaling that drives regenerative growth, and sustain that signaling long enough for regeneration to complete. How these key signals are sustained is unclear. To gain a comprehensive view of the changes in gene expression that occur during regeneration, we performed whole-genome mRNAseq of actively regenerating tissue from damaged Drosophila wing imaginal discs. We used genetic tools to ablate the wing primordium to induce regeneration, and carried out transcriptional profiling of the regeneration blastema by fluorescently labeling and sorting the blastema cells, thus identifying differentially expressed genes. Importantly, by using genetic mutants of several of these differentially expressed genes we have confirmed that they have roles in regeneration. Using this approach, we show that high expression of the gene moladietz (mol), which encodes the Duox-maturation factor NIP, is required during regeneration to produce reactive oxygen species (ROS), which in turn sustain JNK signaling during regeneration. We also show that JNK signaling upregulates mol expression, thereby activating a positive feedback signal that ensures the prolonged JNK activation required for regenerative growth. Thus, by whole-genome transcriptional profiling of regenerating tissue we have identified a positive feedback loop that regulates the extent of regenerative growth.

Dissociation of imaginal disc cells has been carried out previously to enable flow cytometry and cell sorting to analyze cell cycle progression, cell size, gene expression, and other aspects of imaginal tissues. However, the lengthy dissociation protocols employed may alter gene expression, cell behavior and overall viability. Here we describe a new rapid and gentle method of dissociating the cells of wing imaginal discs that significantly enhances cell viability and reduces the likelihood of gene expression changes. Furthermore, this method is scalable, enabling collection of large amounts of sample for high-throughput experiments without the need for data-distorting amplifications.

The imaginal discs of the genetically tractable model organism Drosophila melanogaster have been used to study cell-fate specification and plasticity, including homeotic changes and regeneration-induced transdetermination. The identity of the reprogramming mechanisms that induce plasticity has been of great interest in the field. Here we identify a change from antennal fate to eye fate induced by a Distal-less-GAL4 (DllGAL4) P-element insertion that is a mutant allele of Dll and expresses GAL4 in the antennal imaginal disc. While this fate change is not induced by tissue damage, it appears to be a hybrid of transdetermination and homeosis as the GAL4 expression causes upregulation of Wingless, and the Dll mutation is required for the fate change. Neither GAL4 expression nor a Dll mutation on its own is able to induce antenna-to-eye fate changes. This plasticity appears to be unique to the DllGAL4 line, possibly due to cellular stress induced by the high GAL4 expression combined with the severity of the Dll mutation. Thus, we propose that even in the absence of tissue damage, other forms of cellular stress caused by high GAL4 expression can induce determined cell fates to change, and selector gene mutations can sensitize the tissue to these transformations.

1 2 Regeneration after injury happens in a complex environment that requires precise 3 orchestration of cell proliferation and establishment of correct patterning and cell-fate 4 specification to ensure a fully functional outcome. Regenerative growth needs to be 5 controlled and constrained to prevent overgrowth and to allow differentiation. However, 6 the factors that are required to restrict regeneration to facilitate patterning of the 7 regenerating tissue and establishment of correct cell fates have not been identified. 8Using a genetic ablation system in the Drosophila wing imaginal disc, we have identified 9 the gene brain tumor (brat) as a protective factor that shields the regenerating tissue 10 from excessive pro-growth gene activation and enables correct patterning and cell-fate 11 specification. Regenerating discs with reduced levels of brat are unable to pattern 12 correctly resulting in adult wings with a disrupted wing margin. This mis-patterning is 13 due to elevated levels of the pro-growth factor Myc and the self-renewal factor Chinmo, 14 which lead to suppression of the cell fate-specification gene cut (ct). Thus, Brat protects 15 regenerating tissue from erroneous patterning by constraining expression of pro-16 regeneration genes. 17 18 Introduction 19Regeneration is the remarkable process by which some organisms replace tissues and 20 organs after damage such that both morphology and function are restored. Complete 21 regeneration requires several steps to occur correctly including wound healing, cell 22 the process of regeneration was traditionally thought to be a redeployment of earlier 31 developmental steps (9,(26)(27)(28)(29). However, recent evidence suggests that regeneration is 32 not a simple reiteration of development but can employ regeneration-specific regulatory 33 mechanisms (3,25,(30)(31)(32)(33)(34). Indeed, faithful regeneration likely requires additional 34 mechanisms, since regrowth happens in the presence of wound-response signaling and 35 in a developed juvenile or adult organism. Additionally, pro-growth pathways that are 36 used during normal development are often activated in new ways and at higher 37 strengths in the regenerating tissue (2,7,15,23). These augmented pro-growth signals 38 must decline as regeneration progresses to prevent unrestrained growth and to enable 39 re-establishment of pattern and cell-fate specification. Thus, regeneration-specific 40 growth suppressors and additional patterning factors are likely used to terminate 41 regeneration and allow differentiation (reviewed in 35). However, despite our 42 understanding of the pro-growth signals needed for regeneration, we do not yet know 43 what distinct regeneration-specific factors exist in different model organisms to restrain 44 growth and promote re-patterning of regenerating tissue. 45 4 46 Drosophila melanogaster imaginal discs, precursors of adult fly appendages, are simple 47 columnar epithelia that have well-characterized, complex expression of patterning 48 genes that determine cell-fate spe...

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