Transcription of heat shock gene loci versus non-heat shock loci in Chironomus polytene chromosomes: evidence for heat-induced formation of novel putative ribonucleoprotein particles (hsRNPs) in the major heat shock puffs

Abstract

The heat shock response of Chironomus polytene chromosomes was reexamined. The in vivo effects of heat shock on chromosomal [3H]uridine labeling, RNA polymerase II distribution and ribonucleoprotein (RNP) formation were investigated. One primary result is a clarification of the number and location of chromosomal sites strongly induced by treatment at 37 degrees C for 60 min. In total, seven major heat shock loci were identified by transcription autoradiography in Chironomus tentans: I-20A, II-16B, II-10C, II-4B, II-1C, III-12B, and IV-5C. Secondly, combining immunofluorescence with transcription autoradiography, I find RNA polymerase II occurring after heat shock at multiple chromosomal sites that were also active under normal conditions (20 degrees C). Furthermore, the results demonstrate conclusively that the presence of RNA polymerase II at heat shock and non-heat shock loci is generally correlated with [3H]uridine labeling during heat shock. These latter results extend and corroborate previous findings. Thirdly, the most striking result of this study was revealed in ultrathin sections of puffs by electron microscopy: I discerned a site-specific ultrastructural difference in putative RNP particles between heat shock versus non-heat shock loci. At least three of the seven induced major heat shock puffs (I-20A, III-12B, IV-5C) were observed to contain globular particles that were different, i.e. significantly larger, 250-1,000 A in diameter with a prominent 500-750 A class, than RNP particles of other loci under non-heat shock conditions. These large heat shock puff particles presumably represent nascent or newly synthesized heat shock RNA associated with protein(s) to form heat shock RNPs (hsRNPs). This finding suggests the possible involvement of novel RNPs (hsRNPs) in transcriptional regulation or heat shock RNA turnover and may stimulate further molecular investigations on this subject in both cell physiological and structural terms. I conclude that the locus-specific putative hsRNPs are an intrinsic property of greatly increased heat shock gene transcription.

Specific combinations of SR proteins associate with single pre-messenger RNAs in vivo and contribute different functions

“…It is also possible to identify the heat shock genes in chromosome preparations (Sass, 1995). We observed differential binding of SR proteins to heat shock pre-mRNA (Fig.…”

Transcription regulation during stable elongation by a reversible halt of RNA polymerase II

“…It was well known that the transcription of most genes of C. tentans could be down-regulated by heat shock (Sass, 1995). However, that transcription is not generally stopped in the nucleus; instead, heat shock–responsive genes become activated or more strongly expressed.…”

A novel computational approach of image analysis to quantify behavioural response to heat shock in Chironomus Ramosus larvae (Diptera: Chironomidae)

“…Chironomid midges show adaptations to a wide range of temperature fluctuations (Oliver 1971;Ferrington 2008) and appropriately qualify as models to study temperature stress. Previously, several works on HSPs and heat shock inducible chromosomal loci were reported mainly in two European species, namely, Chironomus tentans Fabricius and Chironomus thummi (Kieffer) (Tanguay and Vincent 1981;Lezzi 1984;Carretero et al 1991;Sass 1995;Martinez et al 1997;Morcillo et al 1997) and in one Indian species, Chironomus striatipennis Kieffer (Nath and Lakhotia 1989). In the present study, a tropical Indian species, Chironomus ramosus Chaudhuri, Das and Sublette, colonized in the laboratory (Nath and Godbole 1998) has been chosen to study behavioural response to heat shock.…”