Are mucin genes yet to be cloned expressed by human middle ear mucosa?

Abstract

Middle ear mucosa is a modified respiratory epithelium and five genes for secreted mucins (MUCs 2, 3, 4, 5AC, 5B and 8) are expressed in the airways. In this study we have compared the composition predicted by the gene sequences of these mucins with that of mucins isolated from middle ear effusions. Three groups of mucins, (1) thick and (2) thin from anatomically normal children and (3) effusions from children with a cleft palate were studied. Amino acid analysis was performed on glycopeptide fragments corresponding to the characteristic tandem repeat domains of cloned mucin genes. There were marked differences both between the three mucin pools and from the tandem repeat sequences of the five cloned genes expressed in the airways. Serine, threonine and proline contributed 44%, 29% and 36% from groups (1) (2) and (3)respectively, in the ratios (2.4 : 2.9 : 1) (5 : 1 : 1) and (3.5 : 1 : 1.5).The serine to threonine ratio in thick effusions is similar to that found in MUC 4; however, the high proportion of serine in mucin from groups (2) and (3) is novel. Therefore, more than one mucin gene product is secreted by the human middle ear mucosa and further mucin genes expressed by the middle ear are yet to be cloned.

The aetiology of otitis media with effusion: a review

“…Middle ear effusions contain at least two different populations of mucin molecule, coded for by different genes. Two of the mucins have had their gene of origin determined (respiratory mucins MUC 5AC and MUC 5B; see below), but based on their amino acid analysis, other mucins yet to be identified may be present 91,92 …”

“…Surgical repair of cleft palate leads to measurable improvement in eustachian function and middle ear pressure, 188 but does not, however, seem to alter the incidence of OME 185,186 , 189 . Negative pressure does not explain why cleft palate children's effusions should differ in biochemical composition from those in anatomically normal children 91,92 , 190 . In addition, bacteria can be cultured from 53% to 55% of cleft palate children's effusions, compared to 32% of non‐cleft palate children's effusions 18,191 .…”