Activated Ras/JNK driven Dilp8 in imaginal discs adversely affects organismal homeostasis during early pupal stage inDrosophila, a new checkpoint for development

Abstract

One sentence AbstractElevated JNK activity following predominant over-expression of activated Ras or Reaper or Tak1 in Drosophila larval eye discs does not delay pupation but reduces post-pupariation ecdysone pulse via elevated Dilp8 and reduced Ptth, which results in early pupal death. AbstractWe examined reasons for early pupal death following expression of certain transgenes with predominantly eye-disc specific GMR-GAL4 or sev-GAL4 drivers in Drosophila. The GMR-GAL4 or sev-GAL4 driven expression of UAS-Ras1 V12 transgene, producing activated Ras, resulted in early (~25-30Hr after pupa formation, APF) and late pupal death, respectively. Coexpression of UAS-hsrω-RNAi transgene or EP3037 to down or up-regulate the hsrω lncRNAs with sev-GAL4>UAS-Ras1 V12 advanced the death to 25-30Hr APF. The normal 8-12Hr APF ecdysone surge was absent in the early dying pupae. Exogenous ecdysone provided between 8-20Hr APF partially suppressed their early death. Microarray, qRT-PCR and immunostaining revealed substantial increase in some JNK pathway members in late larval eye discs, and of Dilp8 in eye discs, reduced transcripts of ptth in brain lobes and of ecdysone biosynthesis enzymes in prothoracic glands of 8-9Hr old pupae in genotypes that show early pupal death. We propose that the high JNK activity in eye discs of GMR-GAL4>UAS-Ras1 V12 and sev-GAL4>UAS-Ras1 V12 with altered hsrω transcript levels triggers greater Dilp8 secretion from them soon after pupa formation, which inhibits post-pupal ecdysone synthesis in prothoracic gland, leading to early pupal death. The early pupal death following GMR-GAL4 driven expression of UAS-rpr or UAS-tak1 was also associated with comparable enhanced JNK and Dilp8 signaling in eye discs. This study highlights how mis-regulated signaling in one tissue can have global deleterious consequences through downstream events in other tissues, reemphasizing role of inter organ signaling in life of an organism.

Altered levels ofhsromegalncRNAs further enhance Ras signaling during ectopically activated Ras induced R7 differentiation inDrosophila

“…Evolution of multi-cellularity and the associated division of labour between different cell types has necessitated inter-cellular signaling pathways with complex network of regulatory circuits. The evolution of biological complexity has also been paralleled by substantial increase in the non-coding component in diverse genomes, and there is increasing realization in recent years that the large varieties of short and long non-coding RNAs (lncRNA) have great roles in cell signaling and gene regulation (Geisler and Coller, 2013;Huang et al, 2013;Jose, 2015;Lakhotia, 2016;Lakhotia, 2017a;Lakhotia, 2017b;Mattick and Makunin, 2006;Morris and Mattick, 2014;Peng et al, 2017). The lncRNAs like acal, mrhl, CRNDE, LncND, and URHC have been reported to regulate JNK, Wnt, insulin, Notch and ERK/MAPK signaling pathways, respectively (Arun et al, 2012;Ellis et al, 2014;Katsushima et al, 2016;Ríos-Barrera et al, 2015;Xu et al, 2014).…”

“…The lncRNAs like acal, mrhl, CRNDE, LncND, and URHC have been reported to regulate JNK, Wnt, insulin, Notch and ERK/MAPK signaling pathways, respectively (Arun et al, 2012;Ellis et al, 2014;Katsushima et al, 2016;Ríos-Barrera et al, 2015;Xu et al, 2014). Besides their roles in developmental regulation (Katsushima et al, 2016;Kotake et al, 2016;Lakhotia, 2017b;Misawa et al, 2017;Zhang et al, 2017a), diverse lncRNAs have been reported to interact with components of the various signaling pathways in cancer, activating or repressing their strength and thus affecting outcomes like cell proliferation or apoptosis (Lakhotia, 2016;Liu et al, 2015;Wang et al, 2015). An earlier study (Ray and Lakhotia, 1998) from our laboratory showed that mutant alleles of ras (ras E62K and ras D38N ) dominantly enhanced the lethality due to nullisomic condition of the hsrω gene, which produces multiple lncRNAs (Lakhotia, 2011;Lakhotia, 2017a).…”

“…These findings have implications for modulation of Ras signaling in disease conditions like cancer by lncRNAs functionally analogous to those produced by the hsrω gene. Initial results of this study were published as pre-print archive (Ray and Lakhotia, 2017).…”

Activated Ras/JNK driven Dilp8 in imaginal discs adversely affects organismal homeostasis during early pupal stage in Drosophila, a new checkpoint for development

“…An early version of this study was published as a preprint. 12 This study shows that elevated Ras signaling can also contribute to Dilp8 expression and that activated Ras signaling in a particular tissue has far-reaching consequences on distant organs. It also highlights susceptibility of certain stages of development to specific changes in signaling events, particularly that of Dilp8 on pupal developmental processes and its importance as messenger between epithelia and brain.…”

“…These results thus unravel the early pupal ecdysone surge as a new checkpoint for Dilp8 action and explain the intriguing results noted in several other studies that expression of certain transgenes by predominantly eye disc specific GAL4 drivers is associated with pupal lethality. An early version of this study was published as a preprint …”