BackgroundOysters have important ecological functions in their natural environment, acting as global carbon sinks and improving water quality by removing excess nutrients from the water column. During their life-time oysters are exposed to a variety of pathogens that can cause severe mortality in a range of oyster species. Environmental stressors encountered in their habitat can increase the susceptibility of oysters to these pathogens and in general have been shown to impact on oyster immunity, making immune parameters expressed in these marine animals an important research topic.ResultsPaired-end Illumina high throughput sequencing of six S. glomerata tissues exposed to different environmental stressors resulted in a total of 484,121,702 paired-end reads. When reads and assembled transcripts were compared to the C. gigas genome, an overall low level of similarity at the nucleotide level, but a relatively high similarity at the protein level was observed. Examination of the tissue expression pattern showed that some transcripts coding for cathepsins, heat shock proteins and antioxidant proteins were exclusively expressed in the haemolymph of S. glomerata, suggesting a role in innate immunity. Furthermore, analysis of the S. glomerata ORFs showed a wide range of genes potentially involved in innate immunity, from pattern recognition receptors, components of the Toll-like signalling and apoptosis pathways to a complex antioxidant defence mechanism.ConclusionsThis is the first large scale RNA-Seq study carried out in S. glomerata, showing the complex network of innate immune components that exist in this species. The results confirmed that many of the innate immune system components observed in mammals are also conserved in oysters; however, some, such as the TLR adaptors MAL, TRIF and TRAM are either missing or have been modified significantly. The components identified in this study could help explain the oysters’ natural resilience against pathogenic microorganisms encountered in their natural environment.

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IntroductionBody colouration in animals can have a range of functions, with predator protection an important aspect of colour in crustaceans. Colour determination is associated with the carotenoid astaxanthin, which is taken up through the diet and stabilised in the tissues by the protein crustacyanin. As a variety of genes are found to play a role in colour formation in other systems, a holistic approach was employed in this study to determine the factors involved in Fenneropenaeus merguiensis colouration.ResultsFull length F. merguiensis crustacyanin subunit A and C sequences were isolated. Crustacyanin subunit A and C were found in the F. merguiensis transcriptomes of the muscle/cuticle tissue, hepatopancreas, eye stalk and nervous system, using 454 next generation sequencing technology. Custom microarray analysis of albino, light and dark F. merguiensis cuticle tissue showed genes encoding actin, sarcoplasmic calcium-binding protein and arginine kinase to be 4-fold or greater differentially expressed (p<0.05) and down-regulated in albinos when compared to light and dark samples. QPCR expression analysis of crustacyanin and total astaxanthin pigment extraction revealed significantly (p<0.05) lower crustacyanin subunit A and C gene transcript copy numbers and total astaxanthin levels in albinos than in the light and dark samples. Additionally, crustacyanin subunit A and C expression levels correlated positively with each other.ConclusionsThis study identified gene products putatively involved in crustacean colouration, such as crustacyanin, sarcoplasmic calcium-binding protein and forms of actin, and investigated differences in gene expression and astaxanthin levels between albino, light and dark coloured prawns. These genes open a path to enhance our understanding of the biology and regulation of colour formation.

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Background: Human activities have led to a substantial increase in carbon dioxide (CO 2 ) emission, with further increases predicted. A RNA-Seq study on adult Saccostrea glomerata was carried out to examine the molecular response of this bivalve species to elevated pCO 2 . Results: A total of 1626 S. glomerata transcripts were found to be differentially expressed in oysters exposed to elevated pCO 2 when compared to control oysters. These transcripts cover a range of functions, from immunity (e.g. pattern recognition receptors, antimicrobial peptides), to respiration (e.g. antioxidants, mitochondrial respiratory chain proteins) and biomineralisation (e.g. carbonic anhydrase). Overall, elevated levels of CO 2 appear to have resulted in a priming of the immune system and in producing countermeasures to potential oxidative stress. CO 2 exposure also seems to have resulted in an increase in the expression of proteins involved in protein synthesis, whereas transcripts putatively coding for proteins with a role in cilia and flagella function were down-regulated in response to the stressor. In addition, while some of the transcripts related to biomineralisation were up-regulated (e.g. carbonic anhydrase 2, alkaline phosphatase), a small group was down-regulated (e.g. perlucin). Conclusions: This study highlighted the complex molecular response of the bivalve S. glomerata to expected near-future ocean acidification levels. While there are indications that the oyster attempted to adapt to the stressor, gauged by immune system priming and the increase in protein synthesis, some processes such cilia function appear to have been negatively affected by the elevated levels of CO 2 .