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

ABSTRACT

We examined interactions between the 83 kDa heat-shock protein (Hsp83) and hsrω long noncoding RNAs (lncRNAs) inhsrω66 Hsp90GFP homozygotes, which almost completely lack hsrω lncRNAs but over-express Hsp83. All +/+; hsrω66Hsp90GFP progeny died before the third instar. Rare Sp/CyO; hsrω66 Hsp90GFP reached the third instar stage butphenocopied l(2)gl mutants, becoming progressively bulbous and transparent with enlarged brain and died after prolongedlarval life. Additionally, ventral ganglia too were elongated. However, hsrω66 Hsp90GFP/TM6B heterozygotes, carrying +/+ or Sp/CyO second chromosomes, developed normally. Total RNA sequencing (+/+, +/+; hsrω66/hsrω66, Sp/CyO; hsrω66/hsrω66, +/+; Hsp90GFP/Hsp90GFP and Sp/CyO; hsrω66 Hsp90GFP/hsrω66 Hsp90GFP late third instar larvae) revealedsimilar effects on many genes in hsrω66 and Hsp90GFP homozygotes. Besides additive effect on many of them, numerousadditional genes were affected in Sp/CyO; hsrω66 Hsp90GFP larvae, with l(2)gl and several genes regulating the centralnervous system being highly down-regulated in surviving Sp/CyO; hsrω66 Hsp90GFP larvae, but not in hsrω66 orHsp90GFP single mutants. Hsp83 and several omega speckle-associated hnRNPs were bioinformatically found topotentially bind with these gene promoters and transcripts. Since Hsp83 and hnRNPs are also known to interact, elevatedHsp83 in an altered background of hnRNP distribution and dynamics, due to near absence of hsrω lncRNAs and omegaspeckles, can severely perturb regulatory circuits with unexpected consequences, including down-regulation of tumoursuppressor genes such as l(2)gl.