Despite these efforts, the precise annotation of these alternatively spliced MUC2 transcripts remains incomplete, and the length of the PTS domain, which is predicted to span 55�C110 cassettes, remains highly polymorphic within the human population. Although the biological relevance of these alternatively spliced products in human is not fully understood, it is believed that they are associated with pathogenesis of intestinal diseases. Although functional studies in mice have indicated that Muc2 plays roles in the biology and health of the gut, the function of the PTS domain in mice is less clear, due to the annotation of a relatively short and imprecise repetitive cassette. Evolutionary studies predict that the gel forming mucins share a common ancestor with lower metazoa, as their domain structures are well conserved across a wide range of species from invertebrates to humans. However, relatively few MUC genes have been identified in avians and amphibians. The first Mucin gene cloned in chicken was ovomucin alpha-subunit, now annotated as MUC5B. In silico predictions and annotation of short mRNAs and expressed sequence tags have generated a putative partial MUC2 cDNA in chicken. However, these studies have provided very little functional annotation evidence of the 3,4,5-Trimethoxyphenylacetic acid genomic organization of the chicken MUC2 locus. To determine the structure, expression, biosynthesis and gene signatures of intestinal mucins from a functional and evolutionary perspective, we cloned the chicken MUC2 cDNA that encodes the MUC2 peptide backbone. We achieved this by analyzing and assembling more than 85 cDNA clones that were generated by overlapping RT-PCR products, rapid amplification of cDNA ends, sequencing of ESTs, and incorporating functional annotation data from the UCSC database and NCBI. We also Folinic acid calcium salt pentahydrate compared our sequence to the predicted chicken cDNA. We found that the 11,359 bp chicken cDNA spans 74.5 kb of genomic DNA and is comprised of at least 64 exons. MUC2 is expressed in multiple regions of the gastrointestinal tract, and we detected transcripts as early as embryonic day 14.5. We found several alternatively spliced products, and characterized the splice junctions of one of these transcripts. We determined that the chicken MUC2 protein is remarkably similar to human and mouse outside of the central PTS domain, but is 
highly divergent within this central repetitive structure. In humans, this PTS domain is highly glycosylated by Oglycans in the Golgi, and it is predicted that these posttranslational modifications largely contribute to the innate immune response, as proteolytic cleavage of these sugar chains occurs in the outer mucus layer when these molecules come into contact with foreign pathogens. It will be interesting to compare the posttranslational modifications in chicken with other species, especially given the high degree of divergence in this region. It has been over two decades since the initial cloning of the first intestinal mucin gene in humans. Although the physiological implications and disease associations of mucins on various mucosal surfaces have been well recognized, many questions remain as to how and why the gene architecture of this family contributes to diverse protein modifications that may display distinct functionalities. Different species demonstrate structural and sequence conservations as well as their own uniqueness. Chicken, the moststudied and characterized avian species, bridges the evolutionary gap between mammals and non-amniote vertebrates.