Spatiotemporal expression of flk-1 in pulmonary epithelial cells during lung development.
Vascular endothelial growth factor-A (VEGF-A) responsive effects mediated via the receptors fetal liver kinase-1 (flk-1) and fms-like tyrosine kinase (flt-1), are key processes of pulmonary vascular development. Flk-1 has been shown to be involved in early embryonic lung epithelial to endothelial crosstalk and branching morphogenesis. Recent reports suggested a role of VEGF-A in lung epithelial cell function. Based on these observations, we hypothesize that epithelial flk-1 has a unique function in pulmonary development. Thus, the aim of this study is to elucidate spatiotemporal expression of flk-1 during lung development with respect to the epithelial system. Embryonic lungs were screened for flk-1 messenger RNA and protein at daily intervals, including postnatal stages. From Embryonic Day (ED) 12.5 through ED 15.5, flk-1 expression was restricted to the early vascular primitive network, while from ED 16.5 on flk-1 was detectable in the epithelial system and persisted there postnatally. At postnatal stages, flk-1 expression was increasingly restricted to individual cells in the alveolar septa. Isolation and in vitro cultivation of alveolar epithelial cells confirmed flk-1 expression and showed VEGF secretion into the supernatant. To our knowledge, this is the first murine study characterizing epithelial flk-1 expression at different stages throughout lung organogenesis until birth and at postnatal stages. To confirm epithelial flk-1 expression, we performed reporter gene analysis of the flk-1 promoter in vivo. Investigations on transgenic mouse strains, containing either a complete or incomplete flk-1 promoter driving expression of the lacZ reporter gene, suggested differential flk-1 regulation in endothelial and epithelial cells.
Ahlbrecht
Katrin
K
University of Giessen Lung Center, Department of Internal Medicine, University Hospital Giessen, Giessen, Germany. Katrin.Ahlbrecht@innere.med.uni-giessen.de.
Schmitz
Judith
J
Seay
Ulrike
U
Schwarz
Christine
C
Mittnacht-Kraus
Rita
R
Gaumann
Andreas
A
Haberberger
Rainer V
RV
Herold
Susanne
S
Breier
Georg
G
Grimminger
Friedrich
F
Seeger
Werner
W
Voswinckel
Robert
R
D000818:Animals; D000831:Animals, Newborn; D002478:Cells, Cultured; D004730:Endothelium, Vascular / Q000378:metabolism; D004847:Epithelial Cells / Q000378:metabolism*; D018507:Gene Expression Regulation, Developmental; D008168:Lung / Q000196:embryology / Q000254:growth & development / Q000378:metabolism*; D051379:Mice; D008822:Mice, Transgenic; D011650:Pulmonary Alveoli / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D012333:RNA, Messenger / Q000096:biosynthesis; D020545:Respiratory Mucosa; D042461:Vascular Endothelial Growth Factor A / Q000502:physiology; D040301:Vascular Endothelial Growth Factor Receptor-2 / Q000096:biosynthesis* / Q000235:genetics
D012333:RNA, Messenger; D042461:Vascular Endothelial Growth Factor A; D040301:Vascular Endothelial Growth Factor Receptor-2