Over-expression of Hsp83 in grossly depleted hsrω lncRNA background causes synthetic lethality and l(2)gl phenocopy in Drosophila

We examined interactions between the 83 kDa heat-shock protein (Hsp83) and hsrω long noncoding RNAs (lncRNAs) in hsrω 66 Hsp90GFP homozygotes, which almost completely lack hsrω lncRNAs but over-express Hsp83. All +/+; hsrω 66 Hsp90GFP progeny died before the third instar. Rare Sp/CyO ; hsrω 66 Hsp90GFP reached the third instar stage but phenocopied l(2)gl mutants, becoming progressively bulbous and transparent with enlarged brain and died after prolonged larval life. Additionally, ventral ganglia too were elongated. However, hsrω 66 Hsp90GFP / TM6B heterozygotes, carrying +/+ or Sp/CyO second chromosomes, developed normally. Total RNA sequencing (+/+, +/+; hsrω 66 /hsrω 66 , Sp/CyO ; hsrω 66 /hsrω 66 , +/+; Hsp90GFP/Hsp90GFP and Sp/CyO ; hsrω 66 Hsp90GFP/hsrω 66 Hsp90GFP late third instar larvae) revealed similar effects on many genes in hsrω 66 and Hsp90GFP homozygotes. Besides additive effect on many of them, numerous additional genes were affected in Sp/CyO ; hsrω 66 Hsp90GFP larvae, with l(2)gl and several genes regulating the central nervous system being highly down-regulated in surviving Sp/CyO ; hsrω 66 Hsp90GFP larvae, but not in hsrω 66 or Hsp90GFP single mutants. Hsp83 and several omega speckle-associated hnRNPs were bioinformatically found to potentially bind with these gene promoters and transcripts. Since Hsp83 and hnRNPs are also known to interact, elevated Hsp83 in an altered background of hnRNP distribution and dynamics, due to near absence of hsrω lncRNAs and omega speckles, can severely perturb regulatory circuits with unexpected consequences, including down-regulation of tumour-suppressor genes such as l(2)gl .