Alternatively spliced down syndrome cell adhesion molecule (Dscam) controls innate immunity in crab

Abstract

Alternatively-spliced hypervariable immunoglobulin domainencoding molecules, called Down syndrome cell adhesion molecule (Dscam), have been widely detected as components of the arthropod immune system. Although its ability to specifically bind pathogens and enable phagocytosis of bacteria has been elucidated, the signal transduction mechanisms or effectors that activate post-Dscam-binding pathogens remain poorly characterized. Here, we reveal the alternative splicing exons of Dscam's cytoplasmic tail and its isoforms in the hemocytes of crab (Eriocheir sinensis), showing that the expression of Dscam was acutely induced after an immune challenge, which suggested its functioning for innate immunity. Significantly decreased expression levels of antimicrobial molecular peptides (AMPs) were detected in Dscam-silenced crab hemocytes in vitro, which coincided with their vulnerability to infection by Staphylococcus aureus and higher bacterial concentrations occurring in Dscamsilenced crabs in vivo. Further experimental investigation demonstrated that Dscam-regulated AMP expression via the Src homology (SH)3-binding domain in the first constant exon translated protein of the cytoplasmic tail bound with the SH3 domain of the Dock, an SH3/SH2 adaptor protein required for axon guidance. Dock promoted extracellular signal-regulated kinase (ERK) phosphorylation via indirect binding and then regulated dorsal phosphorylation and translocation from the cytoplasm to the nucleus, subsequently promoting AMP expression for the effective removal of bacteria. To the best of our knowledge, this comprehensive study is the first to highlight the critical role of the alternatively-spliced Dscam cytoplasmic tail in antimicrobial control activity. It also suggests possible crosstalk occurring between Dscam and other pattern recognition receptors.

Immune responses and immunoprotection in crustaceans with special reference to shrimp

“…2018; Li et al . 2019b; Deepika et al, 2020a, 2020b). The IMD pathway plays key roles in controlling Gram‐negative bacterial and virus infections and the JAK/STAT pathway functions in antiviral defence (Li & Xiang 2013).…”

“…Further, scavenger receptor C (SRC) has been identified in shrimp and its antiviral function elucidated (Yang et al 2017). MjSRC in M. japonicus has been reported to function as WSSV phagocytic receptor, which interacts with VP19 of WSSV, Figure 1 Schematic representation of identified innate immune pathways in shrimp -Toll pathway, immuno-deficiency (IMD) pathway and Janus kinase/signal transducers and activators of transcription (JAK/STAT) pathway (modified from Palmer et al 2018;Li et al 2019).…”

“…In a recent study, role of haemocyte membrane-bound Dscam in phagocytosis in Chinese mitten crab, Eriocheir sinensis, has been demonstrated through RNAi-mediated knockdown (Li et al 2018a,b). Moreover, Dscam-silenced haemocytes revealed significant decline in the expression of AMPs (Li et al 2019). In shrimp, P. monodon, complete gene structure of a Dscam has been characterised with different functional domains which involve in specific protein-protein interactions in cellular signal transduction (Aptianyasai et al 2019).…”

“…2013; Li et al . 2019b). Responses of diverse AMPs against microbial infection in shrimp have been reported.…”

Dscam homophilic specificity is generated by high ordercis-multimers coupled withtransself-binding of variable Ig1 in Chelicerata

“…Moreover, ~ 100 sDscam isoforms in scorpion could potentially form a repertoire of 10 8-12 structurally variable assemblies, which is compatible with the order of magnitude of the diversity of antibodies in vertebrates. Notably, pancrustacean Dscam1 isoforms play an immune-protection role in bacterial challenge 42,43,44 . Given the extraordinary diversity and high structural similarity between Chelicerata sDscam and vertebrate antibody and TCR, it is attractive to speculate that sDscam diversity plays a role in invertebrate immunity.…”