Abstract
In the course of both innate and adaptive immunity, cytidine deaminases within the activation induced cytidine deaminase (AID)/apolipoprotein B editing complex (APOBEC) family modulate immune responses by mutating specific nucleic acid sequences of hosts and pathogens. The evolutionary emergence of these mediators, however, seems to coincide precisely with the emergence of adaptive immunity in vertebrates. Here, we show a family of genes in species within two divergent invertebrate phyla—the echinoderm Strongylocentrotus purpuratus and the brachiopod Lingula anatina—that encode proteins with similarities in amino acid sequence and enzymatic activities to the vertebrate AID/APOBECs. The expression of these invertebrate factors is enriched in tissues undergoing constant, direct interactions with microbes and can be induced upon pathogen challenge. Our findings suggest that AID/APOBEC proteins, and their function in immunity, emerged far earlier than previously thought. Thus, cytidine deamination is probably an ancient innate immune mechanism that predates the protostome/deuterostome divergence.
Highlights
In the course of both innate and adaptive immunity, cytidine deaminases within the activation induced cytidine deaminase (AID)/apolipoprotein B editing complex (APOBEC) family modulate immune responses by mutating specific nucleic acid sequences of hosts and pathogens
Activation induced cytidine deaminase (AID)/ apolipoprotein B editing complex (APOBEC) family members participate as the corresponding mutator enzymes in both adaptive and innate immunity
RNAseq data generated from Strongylocentrotus purpuratus immune cells were used to assemble de novo transcriptomes
Summary
In the course of both innate and adaptive immunity, cytidine deaminases within the activation induced cytidine deaminase (AID)/apolipoprotein B editing complex (APOBEC) family modulate immune responses by mutating specific nucleic acid sequences of hosts and pathogens. Activation induced cytidine deaminase (AID)/ apolipoprotein B editing complex (APOBEC) family members participate as the corresponding mutator enzymes in both adaptive and innate immunity. The most evolutionary ancient enzymes in this group that have been characterized are two cytidine deaminases (CDAs) within the agnathan lineage, which are involved in somatic rearrangement of the variable lymphocyte receptor genes[11]. The presence of these enzymes and related immune functions in both major vertebrate lineages suggests that an ortholog of the AID/ APOBEC family was present in the last common vertebrate ancestor[12]. The role of AID/APOBEC in host defenses is much older than previously anticipated
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