LPS injection reprograms the expression and the 3'UTR of a CAP gene by alternative polyadenylation and the formation of a GAIT element in Ciona intestinalis

Abstract

tThe diversification of cellular functions is one of the major characteristics of multicellular organ-isms which allow cells to modulate their gene expression, leading to the formation of transcripts andproteins with different functions and concentrations in response to different stimuli. CAP genes rep-resent a widespread family of proteins belonging to the cysteine-rich secretory protein, antigen 5 andpathogenesis-related 1 superfamily which, it has been proposed, play key roles in the infection processand the modulation of immune responses in host animals. The ascidian Ciona intestinalis represents agroup of proto-chordates with an exclusively innate immune system that has been widely studied inthe field of comparative and developmental immunology. Using this biological system, we describe theidentification of a novel APA mechanism by which an intronic polyadenylation signal is activated by LPSinjection, leading to the formation of a shorter CAP mRNA capable of expressing the first CAP exon plus19 amino acid residues whose sequence is contained within the first intron of the annotated gene. Fur-thermore, such an APA event causes the expression of a translational controlling cis-acting GAIT elementwhich is not present in the previously isolated CAP isoform and identified in the 3-UTR of other immune-related genes, suggesting an intriguing scenario in which both transcriptional and post-transcriptionalcontrol mechanisms are involved in the activation of the CAP gene during inflammatory response in C.intestinalis.