Developmental expression of mucin genes in the human gastrointestinal system.

Mucin glycoproteins play a key role in the normal function of the epithelium lining the gastrointestinal tract. The expression of mucin genes, MUC 3, 4, 5AC, 5B, 6, 7, and 8 in human fetal tissues was examined to establish the localisation and age of onset of expression of each mucin gene during human development. Mucin gene expression was assayed by mRNA in situ hybridisation. Expression of MUC3 was detected in the small intestine and colon from 13 weeks gestation onwards and at low levels in the main pancreatic duct at 13 weeks only. MUC4 expression was seen at a low level in the colonic epithelium from 13 weeks of gestation but not elsewhere in the gastrointestinal tract. MUC5AC mRNA was detected in the colon at 17 weeks and at high levels in the stomach at 23 weeks. MUC6 transcripts were evident in the pancreatic ducts from 13 weeks of gestation and at high levels in the stomach at 23 weeks. MUC5B, MUC7, and MUC8 transcripts were not detected. Mucin genes are expressed from the early mid-trimester of gestation in the developing human fetal gastrointestinal tract.