Iroquois genes influence proximo-distal morphogenesis during rat lung development

• Published in: American journal of physiology. Lung cellular and molecular physiology Vol. 290; no. 4; pp. L777 - L789
• Main Authors: van Tuyl, Minke, Liu, Jason, Groenman, Freek, Ridsdale, Ross, Han, Robin N. N, Venkatesh, Vikram, Tibboel, Dick, Post, Martin
• Format: Journal Article
• Language: English
• Published: United States 01.04.2006
• Subjects: Animals; Apoptosis - drug effects; Biomarkers - metabolism; Bone Morphogenetic Protein 4; Bone Morphogenetic Proteins - metabolism; Cell Proliferation - drug effects; Drosophila; Embryo, Mammalian - cytology; Embryo, Mammalian - metabolism; Embryo, Mammalian - physiology; Embryonic Development - drug effects; Embryonic Development - genetics; Epithelial Cells - metabolism; Female; Fibroblast Growth Factors - metabolism; Gene Expression; Hedgehog Proteins; Homeodomain Proteins - genetics; In Vitro Techniques; Kruppel-Like Transcription Factors - deficiency; Kruppel-Like Transcription Factors - genetics; Lung - abnormalities; Lung - embryology; Male; Mesoderm - metabolism; Mice; Mice, Mutant Strains; Mutation; Oligonucleotides, Antisense - pharmacology; Rats; Rats, Wistar; Trans-Activators - deficiency; Trans-Activators - genetics; Zinc Finger Protein Gli2
• ISSN: 1040-0605; 1522-1504
• DOI: 10.1152/ajplung.00293.2005

1 Lung Biology Program, Hospital for Sick Children Research Institute, Toronto; Departments of 2 Pediatrics and 3 Physiology, University of Toronto, Toronto, Canada; and 4 Department of Pediatric Surgery, Sophia Children's Hospital, Erasmus University Medical Centre Rotterdam, Rotterdam, The Netherlands Submitted 6 July 2005 ; accepted in final form 9 November 2005 Lung development is a highly regulated process directed by mesenchymal-epithelial interactions, which coordinate the temporal and spatial expression of multiple regulatory factors required for proper lung formation. The Iroquois homeobox ( Irx ) genes have been implicated in the patterning and specification of several Drosophila and vertebrate organs, including the heart. Herein, we investigated whether the Irx genes play a role in lung morphogenesis. We found that Irx1 – 3 and Irx5 expression was confined to the branching lung epithelium, whereas Irx4 was not expressed in the developing lung. Antisense knockdown of all pulmonary Irx genes together dramatically decreased distal branching morphogenesis and increased distention of the proximal tubules in vitro, which was accompanied by a reduction in surfactant protein C-positive epithelial cells and an increase in -tubulin IV and Clara cell secretory protein positive epithelial structures. Transmission electron microscopy confirmed the proximal phenotype of the epithelial structures. Furthermore, antisense Irx knockdown resulted in loss of lung mesenchyme and abnormal smooth muscle cell formation. Expression of fibroblast growth factors (FGF) 1, 7, and 10, FGF receptor 2, bone morphogenetic protein 4, and Sonic hedgehog (Shh) were not altered in lung explants treated with antisense Irx oligonucleotides. All four Irx genes were expressed in Shh- and Gli 2 -deficient murine lungs. Collectively, these results suggest that Irx genes are involved in the regulation of proximo-distal morphogenesis of the developing lung but are likely not linked to the FGF, BMP, or Shh signaling pathways. Iroquois homeobox genes; differentiation; sonic hedgehog; fibroblast growth factor; bone morphogenic protein 4 Address for reprint requests and other correspondence: M. Post, Program in Lung Biology, Hospital for Sick Children Research Inst., 555 Univ. Ave., Toronto, Ontario M5G 1X8, Canada (e-mail: martin.post{at}sickkids.ca )