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Sequence Variations in 185/333 Messages from the Purple Sea Urchin Suggest Posttranscriptional Modifications to Increase Immune Diversity¹

Department of Biological Sciences, George Washington University, Washington, DC 20052

The 185/333 gene family is highly expressed in two subsets of immune cells in the purple sea urchin in response to immune challenges. The genes encode a surprisingly diverse set of transcripts, which is a function of the variable presence or absence of blocks of shared sequences, known as elements that generate element patterns. Diversity is also the result of a significant level of point mutations. Together, variable element patterns and single nucleotide polymorphisms result in many unique transcripts. The 185/333 genes only have two exons, with the variable element patterns encoded entirely within the second exon. The diversity of the gene family may be the result of frequent recombination among the 185/333 genes that generates a mosaic distribution of element sequences among the genes. A comparative analysis of the sequences for the genes and messages from individual sea urchins indicates that these two sequence sets have largely different nucleotide sequences and appear to use different element patterns. Furthermore, the nucleotide substitution patterns between genes and messages reveal a strong bias toward transitions, particularly cytidine to uridine conversions. These data are consistent with cytidine deaminase activity and may represent a novel form of immunological diversification in an invertebrate immune response system.

The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ This research was supported by funding from the National Science Foundation (MCB-0424235) (to L.C.S.) and a Weintraub Fellowship from the George Washington University (to K.M.B.).

² Current address: College of Osteopathic Medicine, Touro University, Henderson, NV 89014.

³ Address correspondence and reprint requests to Dr. L. Courtney Smith, 340 Lisner Hall, 2023 G Street NW, Washington, DC 20052. E-mail address: csmith{at}gwu.edu

⁴ Abbreviations used in this paper: AID, activation-induced cytidine deaminase; APOBEC, apolipoprotein B mRNA editing catalytic component; CR, coding region; EST, expressed sequence tag; gDNA, genomic DNA; FReP, fibrinogen-related protein; NLR, NOD-like receptor; PAMP, pathogen-associated molecular pattern; Polµ, DNA polymerase µ; SNP, single nucleotide polymorphism; SRCR, scavenger receptor cysteine-rich; VCBP, variable chitin-binding proteins.

⁵ The online version of this article contains supplemental material.