Identification of differentially expressed genes of the Pacific oysterCrassostrea gigasexposed to prolonged thermal stress

Abstract

The fluctuating thermal nature of the marine environment induces physiological changes in ectotherms that require molecular and gene expression adjustments [1]. Comparative gene expression studies can be used to characterize these adjustments and lead to a better understanding of organismal responses to environmental change. Gene expression datasets can be clustered into groups of genes that represent different compartments of cellular function, and changes in the expression of genes from these clusters can be used to formulate hypotheses as to how different tissues and whole organisms respond to particular biotic or abiotic stresses. Few studies have addressed changes in gene expression in response to temperature variation on marine organisms. Alterations in gene expression have been observed in fish acclimated to constant temperatures and then exposed to daily temperature fluctuations [2] or to a strong heat stress [3]. However, few molecular investigations have focused on the thermal stress response in marine invertebrates [4,5], particularly in the context of global changes and the potential effects on marine invertebrates [6,7].The Pacific oyster Crassostrea gigas is a eurythermic bivalve mollusc that colonizes most of the western coast of Europe. This species prefers sheltered estuarine waters, where it is found in intertidal and shallow subtidal zones. Within their geographic range, oysters typically experience and respond to seasonal temperatures ranging from 4 to 24°C [8]. In the coldest regions inhabited by C. gigas, such as Brittany, Groups of oysters (Crassostrea gigas) were exposed to 25°C for 24 days (controls to 13°C) to explore the biochemical and molecular pathways affected by prolonged thermal stress. This temperature is 4°C above the summer seawater temperature encountered in western Brittany, France where the animals were collected. Suppression subtractive hybridization was used to identify specific up-and downregulated genes in gill and mantle tissues after 7-10 and 24 days of exposure. The resulting libraries contain 858 different sequences that potentially represent highly expressed genes in thermally stressed oysters. Expression of 17 genes identified in these libraries was studied using real-time PCR in gills and mantle at different time points over the course of the thermal stress. Differential gene expression levels were much higher in gills than in the mantle, showing that gills are more sensitive to thermal stress. Expression of most transcripts (mainly heat shock proteins and genes involved in cellular homeostasis) showed a high and rapid increase at 3-7 days of exposure, followed by a decrease at 14 days, and a second, less-pronounced increase at 17-24 days. A slow-down in protein synthesis occurred after 24 days of thermal stress.Abbreviations CTSL, cathepsin L; EST, expressed sequence tag; HYPK, Huntingtin-interacting protein K; HSP, heat shock protein; LDH, lactate dehydrogenase; MTA-1, metastasis-associated protein 1; SSH, suppression substractive hybridization.

Contrasting transcriptome response to thermal stress in two key zooplankton species, Calanus finmarchicus and C. glacialis

“…In addition, RNA-seq showed upregulation of over 200 transcripts in LTS compared to STS in C. finmarchicus, supporting the contention that LTS generally requires a significant change of expression for many genes to ensure cellular homeostasis (e.g. Meistertzheim et al 2007), while C. glacialis did not reveal to keep homeostasis. Similarly to C. finmarchicus, a higher number and little overlap between differentially expressed genes after LTS compared to STS is observed in the coral Acropora millepora under exposure to elevated temperatures (Meyer et al 2011).…”

“…Glutamate dehydrogenase (gdh), a mitochondrial enzyme that plays a key role in the metabolism of free amino acids, responds to acute salinity stress in the Chinese mitten crab but not in the euryhaline copepod T. californicus (Willett & Burton 2003), and may have an important role in the thermal stress response in C. finmarchicus. The down-regulation of ribosomal protein genes, particularly rpl14, has been found in the copepod T. californicus in response to heat stress (Schoville et al 2012), while large-scale up-regulation of ribosomal proteins in response to heat shock or chronic stress has been found in the Pacific oyster (Meistertzheim et al 2007), suggesting an effort to increase translation capacity or protect ribosomal function through the addition or replacement of ribosomal proteins (Kültz 2005).…”

Assessment of housekeeping genes as internal references in quantitative expression analysis during early development of oyster

“…In previous research, although their expression stability was not validated, several housekeeping genes of C. gigas have been used as internal references; they include α subunit of elongation factor 1 (elf1α) (Fabioux et al, 2004;Badariotti et al, 2007;Gonzalez et al, 2007), actin (Zhang et al, 2011), glyceraldehyde-3-phosphate dehydrogenase (gapdh) (Badariotti et al, 2007;Herpin et al, 2007), 18s rRNA (Meistertzheim et al, 2007) and 28s rRNA (David et al, 2005). However, it is inappropriate to simply assume a gene to be stably expressed without validation, especially given the complex early development of C. gigas.…”

Expression pattern of heat shock proteins during acute thermal stress in the Antarctic sea urchin, Sterechinus neumayeri

“…Protein suppression is associated with the increase of apoptosis, which suggests an important role in cellular perturbation caused by hypoxia [51]. The gene Hyou1 has not been studied thoroughly in marine invertebrates, however, induction under thermal stress, has been observed in the gills of the Crassostrea gigas molluscs [52]. This study is the first to document gene expression with thermal stress in Antarctic marine organisms.…”