Novel isoforms of heat shock transcription factor 1 are induced by hypoxia in the Pacific oyster Crassostrea gigas

Abstract

The Pacific oyster Crassostrea gigas inhabits the intertidal zone and shows tolerance to various stress conditions such as hypoxia and heat shock. However, little is known about the cellular mechanism of responses to these stresses. Heat shock transcription factor 1 (HSF1) regulates the transcription of several genes, including heat shock proteins (HSPs). In this study, we cloned HSF1 from the oyster and investigated its response to air-exposure. The cDNA of oyster Hsf1 contains 2,931 bp, of which 1,389 bp encode a protein of 463 amino acid residues. Moreover, we found that the oyster has seven novel alternatively spliced isoforms, Hsf1b-h, consisting of insertion A with 48 bp, insertion B with 42 bp and/or insertion C with 42 bp. We determined the sequences of oyster genomic DNA containing Hsf1 insertions A, B and C. The results indicated that eight isoforms of Hsf1 are generated from a single Hsf1 gene by alternative splicing without frameshifting. Real-time PCR analysis showed that Hsf1a is expressed constitutively, and the expression of Hsf1b-h and Hsp70 mRNA is induced by air exposure and/or hypoxia. In addition, we found that 11 putative hypoxia response elements, which are hypoxia-inducible factor 1 (HIF-1) binding sequences, are located in the Hsf1 promoter region. These data suggest that the oyster has an HIF-HSF pathway in which HSPs are induced in an HIF-dependent manner, and that it also has a novel mechanism of alternative splicing of Hsf1 in response to hypoxia.

Novel Isoforms of Heat Shock Transcription Factor 1, HSF1γα and HSF1γβ, Regulate Chaperone Protein Gene Transcription

“…Inclusion of exon 11 produces the longer α isoform, whereas exclusion leads to the shorter β isoform. Alternative splicing has also been proposed as the mechanism by which multiple HSF isoforms are generated in other species (22–24). In mammals HSF1 mRNA does seem to be constitutively expressed and transcription is not induced by heat stress (25).…”

Analysis of transcriptional responses of normalizing genes on Crassostrea brasiliana under different experimental conditions

“…The genes GAPDH and EF-1a are commonly used as reference genes in transcriptional studies of many organisms, including C. gigas under a range of embryonic and larval developmental stages, following air exposure, heat shock, hydrocarbon contamination, and bacterial challenge [36][37][38]. The GAPDH gene plays a role in energy metabolism and is 1 of the most commonly used reference genes, it is often referred to as "a classical gene" [39].…”

Hsp70 function and polymorphism, its implications for mollusk aquaculture: a review

“…Recent reports have indicated an intraspecific differential expression of Hsp70 to thermal stimuli (Dong et al, 2010;Kang et al, 2011a;Kawabe & Yokoyama, 2011), which has been associated with the existence of polymorphism in the gene Hsp70 of different species (Bernabucci et al, 2010;Li et al, 2010). It is known that the 3'-end of the Hsp70 gene has a higher number of polymorphic sites (Ravaux et al, 2007;Bernabucci et al, 2010;Montero-Barrientos et al, 2010;Kang et al, 2011a;Li et al, 2011) which could be related to the intrinsic thermo-tolerance of each species as well as individuals.…”

“…The Hsp's can be synthesized by most of the studied species, such as mammals (Basiricò et al, 2011;Li et al, 2011), insects (Zizzari & Ellers, 2011;Calabria et al, 2012), fish (Hofmann et al, 2000;Narum & Campbell, 2010;Dalvi et al, 2012;Liu et al, 2017), mollusks (Jackson et al, 2011;Zerebecki & Sorte, 2011;Lim et al, 2012;Thompson et al, 2012;Brokordt et al, 2015) echinoderms (Dong et al, 2010) and crustaceans (Ravaux et al, 2007). In all these species groups, the heat-shock response is highly conserved, as is the sequence of the genes that control the mechanism (Kawabe & Yokoyama, 2011;Park et al, 2012;Wojstasik & Wisnik, 2012).…”