Over-expression of Hsp83 in grossly depleted hsrω lncRNA background causes synthetic lethality and l(2)gl phenocopy in Drosophila
We examined interactions between Hsp83 and hsr{omega} lncRNAs in hsr{omega}66 Hsp90GFP homozygotes, which almost completely lack hsr{omega} lncRNAs but over-express Hsp83. All +/+; hsr{omega}66 Hsp90GFP progeny died before third instar. Rare Sp/CyO; hsr{omega}66 Hsp90GFP reached third instar stage but phenocopied l(2)gl mutants, dying after prolonged larval life, becoming progressively bulbous and transparent with enlarged brain. Additionally, ventral ganglia were elongated. However, hsr{omega}66 Hsp90GFP/TM6B heterozygotes, carrying +/+ or Sp/CyO second chromosomes, developed normally. Total RNA sequencing (+/+, +/+; hsr{omega}66/hsr{omega}66, Sp/CyO; hsr{omega}66/hsr{omega}66, +/+; Hsp90GFP/Hsp90GFP, and Sp/CyO; hsr{omega}66 Hsp90GFP/hsr{omega}66 Hsp90GFP late third instar larvae) revealed similar effects on many genes in hsr{omega}66 and Hsp90GFP homozygotes. Besides additive effect on many of them, numerous additional genes were affected in Sp/CyO; hsr{omega}66 Hsp90GFP larvae, with l(2)gl and several genes regulating CNS being highly down-regulated in surviving Sp/CyO; hsr{omega}66 Hsp90GFP larvae, but not in hsr{omega}66 or Hsp90GFP single mutants. Hsp83 binds at these gene promoters. Several omega speckle associated hnRNPs too may bind with these genes and transcripts. Hsp83-hnRNP interactions are also known. Thus, elevated Hsp83 in altered hnRNP distribution and dynamics, following absence of hsr{omega} lncRNAs and omega speckles, background can severely perturb regulatory circuits with unexpected consequences, including down-regulation of tumor suppressor gene like l(2)gl.