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Penaeus monodon Dscam (PmDscam) has a highly diverse cytoplasmic tail and is the first membrane-bound shrimp Dscam to
Pin-Hsiang Chou1, Hao-Shuo Chang, I-Tung Chen
1Institute of Biotechnology, College of Bioscience and Biotechnology, National Cheng Kung University, Tainan 701, Taiwan.
Abstract:
Down syndrome cell adhesion molecule (Dscam) seems likely to play a key role in the "alternative adaptive immunity" that has been reported in invertebrates. Dscam consists of a cytoplasmic tail that is involved in signal transduction and a hypervariable extracellular region that might use a pathogen recognition mechanism similar to that used by the vertebrate antibodies. In our previous paper, we isolated a unique tail-less form of Dscam from Litopenaeus vannamei. In this study, we report the first membrane-bound form of shrimp Dscam: PmDscam was isolated from Penaeus monodon, and it occurred in both membrane-bound and tail-less forms. Phylogenetic analysis showed that while the crustacean Dscams from shrimp and water flea did not share a single subclade, they were distinct from the invertebrate Dscam-like molecules and from the insecta Dscams. In the extracellular region, the variable regions of PmDscam were located in N-terminal Ig2, N-terminal Ig3 and the entire Ig7 domain. The PmDscam extracellular variants and transmembrane domain variants were produced by mutually exclusive alternative splicing events. The cytoplasmic tail variants were produced by exon inclusion/exclusion. Based on the genomic organization of Daphnia Dscam's cytoplasmic tail, we propose a model of how the shrimp Dscam genomic locus might use Type III polyadenylation to generate both the tail-less and membrane-bound forms.
Insights
Shrimp Down syndrome cell adhesion molecule (Dscam) exhibits both membrane-bound and tail-less forms, crucial for invertebrate adaptive immunity. Alternative splicing generates extensive extracellular and cytoplasmic tail variants, expanding immune recognition capabilities.
Area of Science:
- Immunology
- Molecular Biology
- Genetics
Background:
- Down syndrome cell adhesion molecule (Dscam) is implicated in invertebrate adaptive immunity.
- Dscam features a signaling cytoplasmic tail and a variable extracellular region for pathogen recognition.
- Previous work identified a tail-less Dscam in Litopenaeus vannamei.
Purpose of the Study:
- To identify and characterize membrane-bound forms of shrimp Dscam.
- To investigate the molecular mechanisms underlying Dscam diversity in Penaeus monodon.
- To analyze the phylogenetic relationships of crustacean Dscam.
Main Methods:
- Isolation of Penaeus monodon Dscam (PmDscam).
- Phylogenetic analysis of crustacean Dscam sequences.
- Analysis of alternative splicing events in PmDscam variants.
- Genomic organization analysis and modeling of Dscam expression.
Main Results:
- The first membrane-bound form of shrimp Dscam (PmDscam) was isolated, existing alongside tail-less forms.
- Phylogenetic analysis revealed distinct clades for shrimp and water flea Dscams, separate from insect Dscams.
- Extracellular and transmembrane variants arise from mutually exclusive alternative splicing.
- Cytoplasmic tail variants are generated by exon inclusion/exclusion.
Conclusions:
- PmDscam contributes to the diversity of immune molecules in shrimp.
- Alternative splicing of PmDscam generates significant molecular variation for immune responses.
- A model is proposed for generating both tail-less and membrane-bound PmDscam forms via Type III polyadenylation.
