Regulation of ascidian Rel by its alternative splice variant

Molecular evolution and in vitro characterization of Botryllus histocompatibility factor

Botryllus schlosseri is a colonial ascidian with a natural ability to anastomose with another colony to form a vascular and hematopoietic chimera. In order to fuse, two individuals must share at least one allele at the highly polymorphic fuhc locus. Otherwise, a blood-based inflammatory response will occur resulting in a melanin scar at the sites of interaction. The single-locus genetic control of allorecognition makes B. schlosseri an attractive model to study the underlying molecular mechanisms. Over the past decade, several candidate genes involved in allorecognition have been identified, but how they ultimately contribute to allorecognition outcome remains poorly understood. Here, we report our initial molecular characterization of a recently identified candidate allodeterminant called Botryllus histocompatibility factor (bhf). bhf, both on a DNA and protein level, is the least polymorphic protein in the fuhc locus studied so far and, unlike other known allorecognition determinants, does not appear to be under any form of balancing or directional selection. Additionally, we identified a second isoform through mRNA-Seq and an EST assembly library which is missing exon 3, resulting in a C-terminally truncated form. We report via whole-mount fluorescent in situ hybridization that a subset of cells co-express bhf and cfuhc(sec). Finally, we observed BHF's localization in HEK293T at the cytoplasmic side of the plasma membrane in addition to the nucleus via a nuclear localization signal. Given the localization data thus far, we hypothesize that BHF may function as a scaffolding protein in a complex with other Botryllus proteins, rather than functioning as an allorecognition determinant.

Alternative splicing in the NF-kappaB signaling pathway

Activation of transcription factor NF-kappaB can affect the expression of several hundred genes, many of which are involved in inflammation and immunity. The proper NF-kappaB transcriptional response is primarily regulated by post-translational modification of NF-kappaB signaling constituents. Herein, we review the accumulating evidence suggesting that alternative splicing of NF-kappaB signaling components is another means of controlling NF-kappaB signaling. Several alternative splicing events in both the tumor necrosis factor and Toll/interleukin-1 NF-kappaB signaling pathways can inhibit the NF-kappaB response, whereas others enhance NF-kappaB signaling. Alternative splicing of mRNAs encoding some NF-kappaB signaling components can be induced by prolonged exposure to an NF-kappaB-activating signal, such as lipopolysaccharide, suggesting a mechanism for negative feedback to dampen excessive NF-kappaB signaling. Moreover, some NF-kappaB alternative splicing events appear to be specific for certain diseases, and could serve as therapeutic targets or biomarkers.

Is there any association between nek3 and cancers with frequent 13q14 deletion?

Chromosomal region 13q14 is frequently deleted in prostate cancer. nek3, a protein kinase related gene, is located on this region. Analysis of the coding region of nek3 showed an A insertion/deletion polymorphism in a stretch of adenines at the end of exon 9, with 2 alleles showing either 7 or 8 adenines. In addition we found a variant human NEK3 transcript, which lacks the entire exon 10 due to alternative splicing. The frequency of A8 allele is statistically higher in prostate cancer samples (p < 0.001) than normal controls, indicating that tumor samples preferentially express a full length protein. On the contrary, normal samples have a higher frequency for the A7 allele, expressing preferentially a shorter protein. To test if this association is a common feature in cancers with frequent 13q14 alterations, we analyzed cell lines established from oral, lung, and hepatocellular cancers. An association between nek3 A insertion/deletion polymorphism and cancers with alterations at 13q14 is observed.

Evidence for the ancient origin of the NF-kappaB/IkappaB cascade: its archaic role in pathogen infection and immunity

The evolutionary conservation of the NF-kappaB transcription factors, from Drosophila to humans, underscores its pivotal role in immune response. Unexpectedly, the canonical NF-kappaB signaling pathway is not functional in the immune system of Caenorhabditis elegans. Therefore, the ancient origin of the NF-kappaB signaling pathway is still unknown. Here, we report the discovery and characterization of a primitive and functional NF-kappaB/IkappaB pathway in the immune defense of a "living fossil," the horseshoe crab, Carcinoscorpius rotundicauda. The ancient NF-kappaB/IkappaB homologues, CrNFkappaB, CrRelish, and CrIkappaB, share numerous signature motifs with their vertebrate orthologues. CrNFkappaB recognizes both horseshoe crab and mammalian kappaB response elements. CrIkappaB interacts with CrNFkappaB and inhibits its nuclear translocation and DNA-binding activity. The activation of the CrNFkappaB is autoregulated by a feedback mechanism mediated by CrIkappaB, the natural inhibitor of CrNFkappaB. We further show that Gram-negative bacteria infection causes rapid degradation of CrIkappaB and nuclear translocation of CrNFkappaB. Infection also leads to an increase in the kappaB-binding activity and up-regulation of immune-related gene expression, like inducible nitric oxide synthase and Factor C, an LPS-activated serine protease. Altogether, our study shows that, although absent in C. elegans, the NF-kappaB/IkappaB signaling cascade remains well conserved from horseshoe crab to humans, playing an archaic but fundamental role in regulating the expression of critical immune defense molecules.

Regulation of NF-kappaB/Rel by IkappaB is essential for ascidian notochord formation

We previously reported that two NF-kappaB/Rel family members are involved in notochord formation of the ascidian Halocynthia roretzi. Here, we present evidence that the NF-kappaB/Rel signaling pathway plays important roles in the notochord formation in another ascidian, Ciona intestinalis. We first found that two NF-kappaB/Rel family members of C. intestinalis, Ci-rel1 and Ci-rel2, are splice variants: Ci-rel1 is a typical member, while Ci-rel2 is a C-terminally truncated short one. Ectopic expression of GFP-fusion proteins in the C. intestinalis notochord revealed that Ci-rel1 transiently moved into the nucleus in the initial tailbud stage, when concomitant expression of Ci-IkappaB, a C. intestinalis IkappaB homologue, was observed, indicating that Ci-rel1 is transiently activated in this stage. Ci-rel1, as well as Ci-rel2, is capable of binding to the kappaB sequence present upstream of Ci-IkappaB, suggesting that Ci-IkappaB is a target gene of Ci-rel1. Reporter gene assay suggests that the expression of Ci-IkappaB in the notochord is controlled by its kappaB sequence. Gene silencing of Ci-IkappaB by injection of the corresponding antisense morpholino oligonucleotide resulted in impairment of notochord formation in C. intestinalis, particularly in a defect in intercalation of notochord cells. Taken together, the results suggest that the regulation of Ci-rel1 by Ci-IkappaB, whose transcription is regulated by Ci-rel1, in the tailbud stage is essential for notochord formation in C. intestinalis.