Forty years of the 93D puff of Drosophila melanogaster

Abstract

The 93D puff of Drosophila melanogaster became attractive in 1970 because of its singular inducibility by benzamide and has since then remained a major point of focus in my laboratory. Studies on this locus in my and several other laboratories during the past four decades have revealed that (i) this locus is developmentally active, (ii) it is a member of the heat shock gene family but selectively inducible by amides, (iii) the 93D or heat shock RNA omega (hsr row) gene produces multiple nuclear and cytoplasmic large non-coding RNAs (hsr row-n, hsr row-pre-c and hsr row-c), (iv) a variety of RNA-processing proteins, especially the hnRNPs, associate with its > 10 kb nuclear (hsr row-n) transcript to form the nucleoplasmic omega speckles, (v) its genomic architecture and hnRNP-binding properties with the nuclear transcript are conserved in different species although the primary base sequence has diverged rapidly, (vi) heat shock causes the omega speckles to disappear and all the omega speckle associated proteins and the hsr row-n transcript to accumulate at the 93D locus, (vii) the hsr row-n transcript directly or indirectly affects the localization/ stability/activity of a variety of proteins including hnRNPs, Sxl, Hsp83, CBP, DIAP1, JNK-signalling members, proteasome constituents, lamin C, ISWI, HP1 and poly(ADP)-ribose polymerase and (viii) a balanced level of its transcripts is essential for the orderly relocation of various proteins, including hnRNPs, RNA pol II and HP1, to developmentally active chromosome regions during recovery from heat stress. In view of such multitudes of interactions, it appears that large non-coding RNAs like those produced by the hsr row gene may function as hubs to coordinate multiple cellular networks and thus play important roles in maintenance of cellular homeostasis.

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

“…A major function of the nuclear hsrω transcripts is to organize the nucleoplasmic omega speckles which primarily regulate the functional availability of hnRNPs and some other key RNA-processing proteins (Lakhotia et al 1999;Prasanth et al 2000;Jolly and Lakhotia 2006;Lakhotia 2011). In view of such fundamental role, it is not surprising that majority of the embryos that have little or subthreshold levels of these transcripts because of the null allele (present results) or global RNAi ) die before hatching.…”

“…The hsrω gene produces multiple noncoding transcripts (Garbe et al 1986), of which the large (>10 kb) nucleus-limited hsrω-n transcripts organize the nucleoplasmic omega speckles (Prasanth et al 2000;Mallik and Lakhotia 2011), which sequester the various hnRNPs and certain other RNAprocessing proteins that are not actively engaged at a given time (Lakhotia et al 1999;Prasanth et al 2000;Jolly and Lakhotia 2006). Our recent studies (Mallik and Lakhotia 2009a, b, 2010, 2011Onorati et al 2011) have revealed that the hsrω RNA also affects, directly or indirectly, activities of DIAP1, CBP, JNK pathway, proteasome, ISWI, lamin C, etc., highlighting roles of these noncoding RNAs in multiple cellular networks (Lakhotia 2011).…”

In Vivo Effects Of Traditional Ayurvedic Formulations in Drosophila melanogaster Model Relate with Therapeutic Applications

“…Therefore, we examined the possibility that these two formulations, especially the mercury based RS, may cause a mild/chronic stress which may result in improved tolerance to a more severe subsequent stress. Several studies in Drosophila have shown that heat shock brings about a rapid and dramatic change in the distribution of nucleoplasmic and chromosome associated hnRNPs so that soon after heat shock, almost all of them get aggregated at the 93D or hsrω locus [23], [27], [28], [50]. Our present observation on the in situ distribution of three different hnRNPs, viz., Hrp36, Hrp38 and Hrp40, do not provide any evidence for the AR- or RS-fed larval cells being under stress since in all cases, the nuclear distribution of the three hnRNPs was qualitatively similar to that seen in normally fed larval cells.…”

Regulation of ISWI chromatin remodelling activity

“…In Drosophila, the activity of the ISWI ATPase was recently found to be regulated by hsrω, a class of functionally conserved developmentally regulated long ncRNA responsible for the assembly and organization of the hnRNP-containing omega speckles (Onorati et al 2011). Omega speckles are specialized nuclear compartments localized in the nucleoplasm close to chromatin edges, containing diverse hnRNPs (Lakhotia 2011). The nucleoplasmic omega speckles play essential roles in storage and sequestration of hnRNP family members and other proteins involved in RNA processing and maturation in normal as well as stressed cells.…”