Disease relevance of Hsp26

• During development, each of the four members of the small heat shock protein family (Hsp27, Hsp26 Hsp23 and Hsp22), which are coordinately induced in response to a heat stress, shows a specific pattern of expression in diverse tissues and cells [1].

High impact information on Hsp26

• Brief treatment of Drosophila cells with flavopiridol leads to a reduction in the accumulation of induced hsp70 and hsp26 RNAs [2].
• Chromatin remodeling by GAGA factor and heat shock factor at the hypersensitive Drosophila hsp26 promoter in vitro [3].
• Genomic footprinting on the Drosophila hsp26 promoter in isolated nuclei has shown that a TATA box binding factor is present before and after induction by heat shock, while three of the seven heat shock consensus sequences 5' of the gene are occupied (presumably by heat shock factor, HSF) specifically on heat shock [4].
• The juxtaposition of these various macromolecules on the DNA suggests a basis for the major DNase I hypersensitive site 5' of hsp26 and a novel tertiary structure for the promoter complex [4].
• Both assays reveal that hsp26 is expressed in numerous tissues during development including spermatocytes, nurse cells, epithelium, imaginal discs, proventriculus and neurocytes [5].

Biological context of Hsp26

• The direct involvement of one of these consensus sequences has been assessed: a 6-bp deletion within the proximal element of the hsp26 gene strongly reduced its inducibility [6].
• Using a P element containing an hsp70-white gene and a copy of hsp26 (marked with a fragment of plant DNA designated pt), we have identified domains that allow for full expression of the white marker (R domains), and others that induce a variegating phenotype (V domains) [7].
• The replacement results in a loss of heat shock-inducible hsp26 expression and drastically diminishes nuclease accessibility in the chromatin of the regulatory region [8].
• Previous studies of the Drosophila melanogaster hsp26 gene promoter have demonstrated the importance of a homopurine*homopyrimidine segment [primarily (CT)n*(GA)n] for chromatin structure formation and gene activation [9].
• To test whether the (CT)n sequence can function through H-DNA in vivo, we have analyzed a series of hsp26-lacZ transgenes with altered sequences in this region [9].

Anatomical context of Hsp26

• SpnA is also shown to interact with meiotic chromosomes during prophase I in the primary spermatocytes of hsp26-spnA transgenic flies [10].

Associations of Hsp26 with chemical compounds

• HSP 26 and 27 are phosphorylated in response to heat shock and ecdysterone in Drosophila melanogaster cells [11].

Physical interactions of Hsp26

• GAGA factor and the TFIID complex collaborate in generating an open chromatin structure at the Drosophila melanogaster hsp26 promoter [8].

Other interactions of Hsp26

• The polymer dramatically inhibited expression of cotransfected hsp70, hsp26, and hsp83 genes, but not cotransfected copia and histone genes [12].
• The tissue-specific patterns of developmental expression of hsp26-lacZ fusion genes inserted into Drosophila melanogaster by germline transformation were analyzed in several transformant lines utilizing a histochemical assay for beta-galactosidase activity on whole animals [5].
• In addition, factors in extracts from heat-shocked embryos blocked exonuclease digestion at sites flanking the heat shock consensus sequences of hsp26 and hsp70 [13].

References