In lung development, the apically constricted columnar epithelium forms numerous buds during the pseudoglandular stage. Subsequently, these epithelial cells change shape into the flat or cuboidal pneumocytes that form the air sacs during the canalicular and saccular (canalicular-saccular) stages, yet the impact of cell shape on tissue morphogenesis remains unclear. Here, we show that the expression of Wnt components is decreased in the canalicular-saccular stages, and that genetically constitutive activation of Wnt signaling impairs air sac formation by inducing apical constriction in the epithelium as seen in the pseudoglandular stage. Organ culture models also demonstrate that Wnt signaling induces apical constriction through apical actomyosin cytoskeletal organization. Mathematical modeling reveals that apical constriction induces bud formation and that loss of apical constriction is required for the formation of an air sac-like structure. We identify MAP/microtubule affinity-regulating kinase 1 (Mark1) as a downstream molecule of Wnt signaling and show that it is required for apical cytoskeletal organization and bud formation. These results suggest that Wnt signaling is required for bud formation by inducing apical constriction during the pseudoglandular stage, whereas loss of Wnt signaling is necessary for air sac formation in the canalicular-saccular stages.
The authors declare no competing or financial interests.
K.F. designed and performed the majority of the experiments and co-wrote the manuscript with the assistance of A.K. H.T.-I. performed mathematical modeling. K.S. generated Mark1 mutant mice. T.K. performed the experiments. A.K. designed experiments, interpreted results and co-wrote the manuscript.
This work was supported by Grants-in-Aid for Scientific Research (2013-2015; No. 25250018 to A.K.) and for Scientific Research on Innovative Areas (2011-2015; No. 23112004 to A.K.) from the Ministry of Education, Science and Culture of Japan and by grants from the Uehara Memorial Foundation.
Microarray data have been deposited in NCBI Gene Expression Omnibus under accession number GSE83391 (https://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE83391).
Supplementary information available online at http://dev.biologists.org/lookup/doi/10.1242/dev.141325.supplemental
- Received June 21, 2016.
- Accepted November 21, 2016.