The large noncoding hsrω-n transcripts are essential for thermotolerance and remobilization of hnRNPs, HP1 and RNA polymerase II during recovery from heat shock in Drosophila

Abstract

The hs-GAL4(t)-driven expression of the hsrω-RNAi transgene or EP93D allele of the noncoding hsrω resulted in global down- or upregulation, respectively, of the large hsrω-n transcripts following heat shock. Subsequent to temperature shock, hsrω-null or those expressing hsrω-RNAi or the EP93D allele displayed delayed lethality of most embryos, first or third instar larvae. Three-day-old hsrω-null flies mostly died immediately or within a day after heat shock. Heat-shock-induced RNAi or EP expression in flies caused only a marginal lethality but severely affected oogenesis. EP allele or hsrω-RNAi expression after heat shock did not affect heat shock puffs and Hsp70 synthesis. Both down- and upregulation of hsrω-n transcripts suppressed reappearance of the hsrω-n transcript-dependent nucleoplasmic omega speckles during recovery from heat shock. Hrp36, heterochromatin protein 1, and active RNA pol II in unstressed or heat-shocked wild-type or hsrω-null larvae or those expressing the hs-GAL4(t)-driven hsrω-RNAi or the EP93D allele were comparably distributed on polytene chromosomes. Redistribution of these proteins to pre-stress locations after a 1- or 2-h recovery was severely compromised in glands with down- or upregulated levels of hsrω-n transcripts after heat shock. The hsrω-null unstressed cells always lacked omega speckles and little Hrp36 moved to any chromosome region following heat shock, and its relocation to chromosome regions during recovery was also incomplete. This present study reveals for the first time that the spatial restoration of key regulatory factors like hnRNPs, HP1, or RNA pol II to their pre-stress nuclear targets in cells recovering from thermal stress is dependent upon critical level of the large hsrω-n noncoding RNA. In the absence of their relocation to pre-stress chromosome sites, normal developmental gene activity fails to be restored, which finally results in delayed organismal death.

AAGAG repeat RNA is an essential component of nuclear matrix inDrosophila

“…[42][43][44][45][46][47][48] Similarly, lncRNA are shown to be involved in organization of heterochromatin, 38,41 paraspeckles, 39,49 nuclear stress bodies and multiple chromatin features. [50][51][52][53] In several other instances, lncRNAs act as guides for chromatin-modifying machinery and mediate the formation of a defined active/inactive chromatin compartment. Recently, GAA-repeat containing RNA was found in the nuclear matrix of mammalian cells.…”

Pleiotropic consequences of misexpression of the developmentally active and stress-inducible non-coding hsrω gene in Drosophila

“…The near ubiquitous presence of hsrω transcripts in Drosophila cells (Bendena et al 1991;Mutsuddi and Lakhotia 1995;Lakhotia et al 2001) and the high degree of embryonic lethality associated with hsrω nullisomics (Mohler and Pardue 1984;Lakhotia and Ray 1996) suggest an essential requirement for this gene in vital housekeeping functions during normal development and differentiation of the fly (reviewed in Lakhotia and Sharma 1996;Lakhotia 2003). Since this gene forms one of the largest and transcriptionally most active puffs after a temperature shock (Mukherjee and Lakhotia 1979) and is uniquely inducible by a variety of amides (Lakhotia andMukherjee 1980, 1984;Tapadia and Lakhotia 1997), these transcripts seem to have a role in management of cellular stress as well (Lakhotia 2003;Jolly and Lakhotia 2006;Lakhotia et al 2011).…”

New Levels of Transcriptome Complexity at Upper Thermal Limits in WildDrosophilaRevealed by Exon Expression Analysis

“…Under heat stress, the noncoding nuclear (intronless) or hsrv-n transcripts regulate RNA processing through the formation of nuclear "speckles" that recruit hnRNPs (heterogeneous nuclear ribonucleoproteins that associate with premRNAs) (Prasanth et al 2000;Jolly and Lakhotia 2006). During recovery, critical levels of hsrv-n are thought to be important in the spatial restoration of RNA processing factors (Lakhotia et al 2012), while elevated cytoplasmic hsrv-c (intron containing) transcript levels during both heat and cold recovery suggest a further role of this gene in thermotolerance (Johnson et al 2011). Here, both transcript sets were heat responsive, although expression of hsrv-c was delayed until recovery consistent with blocked splicing (Bendena et al 1989).…”