Dscam in arthropod immune priming: What is known and what remains unknown

A popular view in the current academic circle is that invertebrates have no adaptive immunity. However, the immune memory and specificity of invertebrates pose a serious challenge to this view and constitute immune priming based on innate immunity. The Down syndrome cell adhesion molecule (Dscam) gene of invertebrates, with approximately 10,000 alternatively spliced isoforms, has a unique characteristic: it specifically binds to different types of bacteria and promotes cell phagocytosis; owing to its antibody-like function, Dscam is a key candidate protein for immune priming. However, the high molecular diversity of Dscam and the gaps and inconsistencies in the existing research make the study of regulation of immune priming by Dscam challenging. In recent years, significant research has been conducted on the Dscam-regulated immune functions in insects and crustaceans, providing preliminary results for Dscam-regulated innate immunity and immune priming, but some important questions remain unresolved. In this review, we summarize the existing knowledge about Dscam-regulated immunity and discuss three yet unanswered questions, the study of which may improve the understanding of the role of Dscam-regulated immune priming in invertebrates.