Mucins are large glycoproteins that cover the epithelial cell surfaces of the respiratory, digestive and urogenital tracts. They form gel-like structures, and are thereby able to protect against harmful molecules and microorganisms. Previous studies have made genome and transcriptome information become available for a large number of species, including ctenophores and choanoflagellates.

Based on profile hidden Markov models (HMMs), researchers from University of Gothenburg and Dr. LANG Tiange of Xishuangbanna Tropical Botanical Garden (XTBG) exploited the novel information to obtain a more accurate and comprehensive account of the evolution of the gel-forming mucins. To make the analysis more effective and accurate, the researchers have used a novel method of identifying mucin-like protein sequences, as well as methods to identify regions in genomes encoding those proteins. They also examined the evolution of the Fcgamma-Binding Protein (FCGBP) protein, a protein with multiple von Willebrand D (VWD) domains known to colocalize with the gel-forming mucins.

The researchers have found a large number of such proteins in Metazoa (any of a group that comprises all animals having the body composed of cells differentiated into tissues and organs and usually a digestive cavity lined with specialized cells), aiding in their classification and allowing evolutionary studies. Most vertebrates had 5 to 6 gel-forming mucin genes and the genomic arrangement of those genes was well conserved throughout vertebrates. They also found that the ovomucin protein was characteristic of reptiles, birds and amphibians.

The researchers had identified proteins with properties of gel-forming mucins in Ctenophora, a group shown to be sister to all other animals, which demonstrated a very early origin of that family of proteins. Their presence in Cnidaria, Porifera, and in Ctenophora (comb jellies) showed that those proteins were present early in metazoan evolution.

A protein resembling the vertebrate FCGBP protein appeared later in evolution as it was observed only in cephalochordates and vertebrates. In human, the FCGBP protein colocalized with mucins in goblet cells and in the mucus.

The study entitled "“Searching the evolutionary origin of epithelial mucus protein components – mucins and FCGBP"” has been published in Molecular Biology and Evolution.