Submitted on June 15, 2006
Accepted on November 10, 2006
MESENCHYMAL MAINTENANCE OF DISTAL EPITHELIAL CELL PHENOTYPE DURING LATE FETAL LUNG DEVELOPMENT
Julie Deimling1, Kate Thompson2, Irene Tseu1, Jinxia Wang3, Richard Keijzer1, Keith Tanswell4, and Martin Post5*
1 Lung Biology Program, Hospital for Sick Children, Toronto, Canada
2 Lung BiologyProgram, Hospital for Sick Children, Toronto, Canada
3 Lung Biology Program, Hospital for Sick children, Toronto, Canada
4 Lung Biology Program, Hospital for Sick Children, Toronto, Canada; Pediatrics, University of Toronto, Toronto, Canada; Physiology, University of Toronto, toronto, Canada
5 Lung Biology Program, Hospital for Sick Children, Toronto, Canada; Pediatrics, University of Toronto, Toronto, Canada; Physiology, University of Toronto, toronto, Canada; Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Canada
* To whom correspondence should be addressed. E-mail: martin.post{at}sickkids.ca.
Classical tissue recombination experiments have reported that at early gestation both tracheal and distal lung epithelium have the plasticity to respond to mesenchymal signals. Herein, we examined the role of epithelial-mesenchymal interactions in maintaining epithelial differentiation at late (E19-E21, term = 22days) fetal gestation in the rat. Isolated distal lung epithelial cells were recombined with mesenchymal cells from lung, skin and intestine and the homotypic or heterotypic recombinant cell aggregates were cultured for up to five days. Recombining lung epithelial cells with mesenchyme from various sources induced a morphological pattern which was specific to the type of inducing mesenchyme. In situ analysis of surfactant protein(SP)-C, SP-B and Clara Cell Secretory Protein (CCSP) expression as well as SP-C and CCSP promoter transactivation experiments revealed that distal lung epithelium requires lung mesenchyme to maintain the alveolar, but not bronchiolar, phenotype. Incubation of lung recombinants with an anti-FGF7 antibody resulted in a partial inhibition of mesenchyme-induced SP-C promoter transactivation. Immunoreactivity for Delta and Lunatic fringe, components of the Notch pathway that regulates cell differentiation, were down-regulated in the heterotypic recombinants. In contrast, Hes1 mRNA expression was increased in these recombinants. Cumulatively, these results suggest that at late fetal gestation, distal lung epithelial cells are not fully committed to a specific phenotype and still have the plasticity to respond to various signals. Their alveolar phenotype is likely maintained by Notch/Notch ligand interactions and mesenchymal factors, including FGF7.
