Uncovering Hemocyanin Subunit Heterogeneity in Penaeid Shrimp using RNA-Seq.

Abstract

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.