The diversity of beta defensins in lungfish (Dipnoi)

Abstract

Abstract Mucosal surfaces are the first line of defense against pathogens. At these surfaces, mucus containing innate and adaptive immune molecules is constantly secreted to protect the animal host. African lungfish are the extant relatives to all tetrapods and have a dual mode of living, swimming in freshwater during the wet seasons and aestivating during the dry seasons. During terrestrialization, African lungfish produce large amounts of mucus that form a dry cocoon to prevent water loss. We recently reported that the lungfish cocoon acts as a bacterial trapping structure and it is rich in antimicrobial peptides (AMPs), specifically beta defensins (BD). As many AMPs, BDs are small amphipathic molecules and mainly cationic. The goal of this study is to provide a full characterization of BD genes from transcriptomes and genomes of different lungfish species. Using the canonical six cysteine motif from vertebrate BD molecules, we searched for all BD genes Protopterus dolloi transcriptomes, the genomes of P. annectens and Australian lungfish (a non-aestivating lungfish, Neoceratodus forsteri). BLASTs searches identified 9 BD genes in P. dolloi transcriptomes with predicted highly cationic characteristics except for BD-7. Sequence alignment and phylogenetic trees indicate that three P. dolloi BD genes may be an intermediate form of AMP between beta and alpha defensins. Genomic analyses indicate that P. annectens BD genes contain 3 exons and 2 introns similar to all defensin genes. Future studies will determine the tissue distribution and antimicrobial function of Protopterus spp. BD molecules and determine their potential application as alternatives to antibiotics. Supported by National Science Foundation Integral Organismal Systems (IOS) award # 1938816