Uncovering Hemocyanin Subunit Heterogeneity in Penaeid Shrimp using RNA-Seq

Aquatic crustaceans can experience low levels of O₂ alone but more often in combination with high levels of CO₂ both in natural estuaries and in aquaculture ponds. Hemocyanin, the respiratory pigment in many crustacean species, facilitates O₂ transport and is documented to change in abundance, structure, and function in response to low O₂ The impacts of high CO₂ on the respiratory pigment are less clear. In this synthesis we bring together data from recently published and new RNA-Seq studies toward the aims of defining the full repertoire of hemocyanin subunits, as well as their differential expression and regulation in the Penaeoidea family in response to low O₂ with or without high CO₂ RNA-Seq data were collected from the hepatopancreas tissues of aquacultured Pacific whiteleg shrimp Litopenaeus vannamei, wild-caught L. vannamei, and wild-caught Atlantic brown shrimp Farfantepenaeus aztecus. De novo assembly yielded high-quality stranded transcriptomes. Manual curation of the hemocyanin subunits from all three groups of penaeid shrimp confirmed the existence of a small γ-type hemocyanin subunit (HcS), greater sequence diversity in the large γ-type hemocyanin subunit than previously identified (HcL1-3 isoforms) and expression of a β-type hemocyanin subunit (HcB) previously unidentified in Penaeid shrimp. Relative abundance of transcripts encoding these hemocyanin isoforms differed within and among the three species/strains. Exposure to low O₂ induced expression of all of the subunits in aquacultured L. vannamei With concurrent exposure to high CO₂, the number of γ-type hemocyanin transcripts decreased while the expression of β-type transcripts remained unchanged. Together with functional data for hemocyanins in the same shrimp species/strains, the RNA-Seq approach shows great promise to provide new insights into the connection between sequence, protein structure, and physiological function of respiratory pigments in this decapod crustacean family.