The mouse Muc5b mucin gene: cDNA and genomic structures, chromosomal localization and expression

We report here the isolation and characterization of the mouse Muc5b mucin gene (mMuc5b). We determined its complete cDNA sequence, its genomic organization, and chromosomal localization. Moreover, we analyzed the expression of this gene by reverse-transcription PCR and in situ hybridization. The structure of the gene was determined from a genomic cosmid clone that encompasses the entire mMuc5b gene, including the 5'-flanking region. The mMuc5b gene spans approximately 36 kb and contains 49 exons. It is located on mouse distal chromosome 7. mMuc5b encodes at least two transcripts by alternative splicing of the second exon, the longest one being 14.9 kb in length. The deduced peptide contains 4782 amino acids. Its central region can be subdivided into 10 imperfect repeats, each composed of a cysteine-rich domain followed by a threonine, serine, and proline-rich mucin-type domain. It is flanked by cysteine-rich domains similar to cysteine-rich domains of pre-pro-von Willebrand factor. Comparison with its human homologue MUC5B revealed common features including high sequence similarities in the 5' and 3' regions, and the conservation of the genomic organization. In contrast, mMuc5b differs from its human homologue, since no highly tandemly repeated sequences could be identified within its central region. mMuc5b is expressed mainly in laryngeal mucous glands, and at a lesser extend in stomach and duodenum.