Abstract
The cysteine aspartic acid-specific protease (caspase) family is distributed across vertebrates and invertebrates, and its members are involved in apoptosis and response to cellular stress. The Zhikong scallop (Chlamys farreri) is a bivalve mollusc that is well adapted to complex marine environments, yet the diversity of caspase homologues and their expression patterns in the Zhikong scallop remain largely unknown. Here, we identified 30 caspase homologues in the genome of the Zhikong scallop and analysed their expression dynamics during all developmental stages and following exposure to paralytic shellfish toxins (PSTs). The 30 caspase homologues were classified as initiators (caspases-2/9 and caspases-8/10) or executioners (caspases-3/6/7 and caspases-3/6/7-like) and displayed increased copy numbers compared to those in vertebrates. Almost all of the caspase-2/9 genes were highly expressed throughout all developmental stages from zygote to juvenile, and their expression in the digestive gland and kidney was slightly influenced by PSTs. The caspase-8/10 genes were highly expressed in the digestive gland and kidney, while PSTs inhibited their expression in these two organs. After exposure to different Alexandrium PST-producing algae (AM-1 and ACDH), the number of significantly up-regulated caspase homologues in the digestive gland increased with the toxicity level of PST derivatives, which might be due to the higher toxicity of GTXs produced by AM-1 compared to the N-sulphocarbamoyl analogues produced by ACDH. However, the effect of these two PST-producing algae strains on caspase expression in the kidney seemed to be stronger, possibly because the PST derivatives were transformed into highly toxic compounds in scallop kidney, and suggested an organ-dependent response to PSTs. These results indicate the dedicated control of caspase gene expression and highlight their contribution to PSTs in C. farreri. This work provides a further understanding of the role of caspase homologues in the Zhikong scallop and can guide future studies focussing on the role of caspases and their interactions with PSTs.
Highlights
Apoptosis regulates a broad range of cellular processes, including stress responses, cell death, growth, and development [1,2,3,4]
We demonstrated that caspase-2/9 genes tended to be expressed in all stages of development and all differentiated organs, whereas the higher expression of caspase-8/10 genes was only observed in the digestive gland and kidney in the adult stage
The number of significantly up-regulated caspase homologues in the digestive gland increased with the toxicity level of paralytic shellfish toxins (PSTs) derivatives
Summary
Apoptosis regulates a broad range of cellular processes, including stress responses, cell death, growth, and development [1,2,3,4]. Caspases (cysteine aspartic acid-specific proteases) are conserved intracellular cysteine-dependent proteases that regulate apoptosis [1,2]. After being activated upon oligomerisation or cleavage at specific aspartate residues, caspases initiate and execute programmed cell death [3]. Based on the functional and structural differences of caspase family members, mammalian caspases are classified into four groups: initiators (caspases-2/8/9/10), executioners (caspases-3/6/7), inflammatory caspases (caspases-1, 4, 5, 11, 12, and 13) [4], and keratinisation-related caspases (caspase-14) [5]. All caspases have a conserved CASc domain that consists of a 5-peptide site consisting of Gln-Ala-Cys-x-Gly (QACxG) (X is R, G, or Q) that is responsible for enzyme catalytic activity [7]. A number of caspase families have been reported in vertebrates, and several studies have explored caspases in invertebrates in the past several decades. The study of invertebrate caspases has been confined to model species such as the roundworm (Caenorhabditis elegans) [8] and fruit fly (Drosophila melanogaster) [8,9]
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