The transcription factor NF-κB in the demosponge Amphimedon queenslandica: insights on the evolutionary origin of the Rel homology domain
The Rel/nuclear factor-kappa B (NF-κB) and nuclear factor of activated T-cells (NFAT) transcription factors contribute to the regulation of an assortment of biological processes by binding DNA with high specificity using their Rel homology domain (RHD). Recently, it has been shown that members of these gene families are present in the genome of the anthozoan cnidarian Nematostella vectensis, indicating that they predate the evolution of the most recent ancestor to living bilaterians. By identifying a single NF-κB gene in the genome of the demosponge Amphimedon queenslandica, a representative of an even earlier branching metazoan lineage, we demonstrate here that the Rel/NF-κB family originated at the dawn of the Metazoa. There is no evidence of RHDs in fungal and choanoflagellate genomes, supporting the notion that the RHD is a metazoan-specific innovation. The A. queenslandica gene (AmqNF-κB) encodes a protein that is highly similar in structure to the vertebrate NF-κB p50/p52 proteins, possessing both a RHD and ankyrin (ANK) repeats. The intact AmqNF-κB contrasts with the N. vectensis NF-κB, which lacks ANK repeats, and suggests that the ancestral metazoan NF-κB was configured identically to contemporary vertebrate and sponge forms. AmqNF-κB is expressed during A. queenslandica embryogenesis, suggesting a developmental role.
KeywordsNuclear factor-kappa B Rel homology domain Ankyrin repeat Porifera
This work was supported by Australian Research Council grants to B.M.D. We gratefully acknowledge the contribution of The United States Department of Energy Joint Genome Institute in the production of Amphimedon (Reniera) genomic and EST sequences used in this study through the Community Sequencing Program. We thank the Director and staff of the University of Queensland Heron Island Research Station for field assistance; the Great Barrier Reef Marine Park Authority for granting permission to carry out this research; and Maja Adamska, Sandie Degnan, Claire Larroux, and Gemma Richards for their valuable advice.
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