Inositol-requiring enzyme 1 involved in regulating hemocyte apoptosis upon heat stress in Patinopecten yessoensis

Transcriptomic profiling of the thermal tolerance in two subspecies of the bay scallop Argopecten irradians

The bay scallop is a eurythermal species with high economic value and now represents the most cultured bivalve species in China. Two subspecies of the bay scallop, the northern subspecies Argopecten irradians irradians Korean population (KK) and the southern subspecies Argopecten irradians concentricus (MM), exhibited distinct adaptations to heat stress. However, the molecular mechanism of heat resistance of the two subspecies remains unclear. In this study, we compared the transcriptomic responses of the two subspecies to heat stress and identified the involved differentially expressed genes (DEGs) and pathways. More DEGs were found in the KK than in the MM when exposed to high temperatures, indicating elevated sensitivity to thermal stress in the KK. Enrichment analysis suggests that KK scallops may respond to heat stress more swiftly by regulating GTPase activity. Meanwhile, MM scallops exhibited higher resistance to heat stress mainly by effective activation of their antioxidant system. Chaperone proteins may play different roles in responses to heat stress in the two subspecies. In both subspecies, the expression levels of antioxidants such as GST were significantly increased; the glycolysis process regulated by PC and PCK1 was greatly intensified; and both apoptotic and anti-apoptotic systems were significantly activated. The pathways related to protein translation and hydrolysis, oxidoreductase activity, organic acid metabolism, and cell apoptosis may also play pivotal roles in the responses to heat stress. The results of this study may provide a theoretical basis for marker-assisted breeding of heat-resistant strains.

Molecular characterization and expression pattern of inositol-requiring enzyme 1 (IRE1) in blunt snout bream (Megalobrama amblycephala): its role of IRE1 involved in inflammatory response induced by lipopolysaccharide

This study aimed to characterize the full-length cDNA of IRE1 from fish Megalobrama amblycephala and investigate its role in the pro-inflammatory response. A full-length cDNA coding IRE1 was cloned from blunt snout bream by RT-PCR and RACE approaches. The cDNA obtained covered 3665 bp with an open reading frame of 3096 bp encoding 1031 amino acids. Sequence alignment and phylogenetic analysis revealed a high degree of conservation (74-92%) among various species, retaining one signal peptide, one luminal domain, one serine/threonine kinase domain, one RNase domain, one activation loop, two N-linked glycosylation sites, and several phosphorylation sites. The highest IRE1 expression was observed in the trunk kidney followed by the brain and spleen, whereas relatively low expression levels were detected in the liver, intestine, adipose, skin, and heart. After lipopolysaccharide (LPS) challenge, the expressions of glucose-regulated protein 78 (GRP78), inositol-requiring enzyme 1 (IRE1), spliced X-box binding protein 1 (XBP1s), C/EBP homologous protein (CHOP), nuclear factor kappa B (NF-κB), tumor necrosis factor alpha (TNFα), and interleukin-6 (IL-6) all increased remarkably in the spleen and brain at different sampling time points, while LPS also upregulated all the genes tested in the intestine except C/EBP homologous protein. Overall, the results indicated that the IRE1 gene of Megalobrama amblycephala shared a high similarity compared with other vertebrates including several bony fish species. Its expression in three tissues was induced remarkably by the LPS challenge, which indicated that IRE1 played a vital role in LPS-induced inflammation on fish.

An activating transcription factor 6 beta (ATF6β) regulates apoptosis of hemocyte during immune response in Crassostrea gigas

The homeostasis of immune cells during immune response is vital for hosts to defend against invaders. Activating transcription factor 6 (ATF6) is an important transcription factor in the unfolded protein response (UPR) to maintaining cellular homeostasis. In the present study, one ATF6 homologue was identified from Pacific oyster Crassostrea gigas (designated as CgATF6β). The full length cDNA of CgATF6β was of 2645 bp with a 1596 bp open reading frame (ORF) encoding a polypeptide of 531 amino acids. The deduced amino acid sequence of CgATF6β was predicted to contain a transmembrane region, a conserved basic leucine zipper (bZIP) domain, a site 1 protease cleavage site, a site 2 protease cleavage site, and a Golgi localization signal. CgATF6β mRNA was constitutively expressed in hemocytes, gill, mantle, gonad, hepatopancreas and labial palp, with a slightly higher expression level in muscle (2.45-fold of that in gill, p < 0.05). After oysters were challenged with Vibrio splendidus, the mRNA expression levels of CgATF6β in hemocytes were significantly up-regulated at 3 h (2.68-fold of that in seawater group, p < 0.01) and peaked at 12 h (3.14-fold of that in seawater group, p < 0.01). The endogenic CgATF6β protein was mainly located in the cytoplasm of oyster hemocytes, and it was significantly transported into the nuclei of hemocytes at 1.5 h after the challenge with V. splendidus. After an injection with CgATF6β dsRNA, the mRNA expression of CgATF6β was knocked down to 0.26-fold of that in dsGFP group (p < 0.01). In CgATF6β dsRNA-injected oysters, the mRNA expressions of glucose-regulated protein 78 (GRP78), calnexin (CNX) and anti-apoptotic B-cell lymphoma-2 (Bcl-2) in hemocytes were significantly decreased at 12 h after V. splendidus challenge, which were 0.65-fold (p < 0.01), 0.54-fold (p < 0.01) and 0.17-fold (p < 0.01) of that in dsGFP-injected oysters, while the apoptotic rate of hemocytes was significantly up-regulated (1.97-fold of that in dsGFP group, p < 0.05). Collectively, these results suggested that CgATF6β was involved in apoptosis inhibition of oyster hemocytes upon V. splendidus challenge by regulating the expression of CgGRP78, CgCNX and CgBcl-2.