Identification, diversity and domain structure analysis of mucin and mucin-like genes in sea anemone Actinia tenebrosa

Abstract

Background: Mucins are part of the glycoprotein family and the main proteinaceous component of mucus. The sea anemone species, Actinia tenebrosa (Phylum Cnidaria) produce large amounts of mucus, which have not been studied in detail. Furthermore, there has only been limited investigation of mucin genes in phylum Cnidaria. Therefore, the aim of current study was to identify and analyse the repertoire mucin genes present in A. tenebrosa and range of other sea anemone species to document their diversity in this group.

Methods: To achieve this aim, we undertook transcriptome sequencing, assembly, and annotation to identify mucin genes in A. tenebrosa.

Results: The results from this study demonstrated a diverse repertoire of mucin proteins, including mucin1-like, mucin4-like, and a range of mucin-like genes in the range of sea anemone species examined. The domain structure of the identified mucin genes was found to be consistent with the conserved domains found in the homologous proteins of vertebrate species. The discovery of a diverse range of mucin genes in sea anemone species provided a basic reference for future mucin studies in cnidarians and could lead to research into their application in the pharmacological, clinical, and cosmetic industries.

Keywords: Actinia tenebrosa; Assembly; Cnidaria; Gel-forming mucin; Mucin genes; Mucus; RNA-sequencing; Sea anemones; Transcriptomes; Transmembrane mucin.

Figure 1. The general structure for mucins.

The figure show in (A) general structure for all mucins indicating the main regions; first, the distinctive terminal regions (N and C), and second, the large central region (PTS). (B) Indicating the conserved gel-forming and transmembrane mucin domains use to identify and classify mucin types.

Figure 2. Actinia tenebrosa in four colourmorph.

The figure shows the sea anemone species A. tenebrosa in four colourmorph. (A) Green and brown A. tenebrosa at low tide; (B) Blue A. tenebrosa fully submerged in water; (C) Red A. tenebrosa fully submerged in water (Images by PGL, 2014, 2015).

Figure 3. The protein domain architectures of A. tenebrosa mucin candidates including domain names.

The protein domain architectures of A. tenebrosa mucin1-like, mucin4-like and mucin-like candidates. (A) Mucin1-like shows the full protein structure of MUC1 including the N-terminus indicated by SP, one SEA domain followed by transmembrane domain on the C-terminus. (B–D) Mucin4-like sequences show the domain structure of MUC4 which is indicated by the NIDO, AMOP and VWD domains, additional domains on the N-terminus presented in the N-terminus in sequence B, and additional single SEA domain presented in the C-terminus in sequence C. (E and F) Mucin-like candidate structures were lacking in the complete collection of MUC4 domains (NIDO, AMOP and VWD) and so they identified only as mucin-like sequences. Varied numbers and sizes of low complexity regions presented among the candidate sequences. The full definitions of candidate mucins domains are available in Table S8.