In this study, we find that WNT7b is the only member of the WNT family of autocrine/paracrine signaling molecules whose expression in the lung is restricted to the airway epithelium during embryonic development. To study the transcriptional mechanisms that underlie this restricted pattern of WNT7b expression, we isolated the proximal 1.0-kb mouse WNT7b promoter and mapped the transcriptional start sites. Transfection of the lung epithelial cell line MLE-15, which expresses WNT7b, shows that the 1.0-kb mouse WNT7b promoter is highly active in lung epithelial cells. This region of the WNT7b promoter contains several DNA binding sites for the important lung-restricted transcription factors TTF-1, GATA6, and Foxa2. Electrophoretic mobility shift assays showed that TTF-1, GATA6, and Foxa2 can bind to a specific subset of their consensus DNA binding sites within the WNT7b promoter. Using cotransfection assays, we demonstrate that TTF-1, GATA6, and Foxa2 can trans-activate the WNT7b promoter in NIH-3T3 cells. Truncation of GATA6 or Foxa2 binding sites reduced the ability of these transcriptional regulators to trans-activate the WNT7b promoter. Finally, the minimal 118-bp region of the mouse WNT7b promoter containing only TTF-1 binding sites was synergistically activated by TTF-1 and GATA6, and we show that TTF-1 and GATA6 physically interact in vivo. Together, these results suggest that WNT7b gene expression in the lung epithelium is regulated in a combinatorial fashion by TTF-1, GATA6, and Foxa2.

Recent advances in single-cell techniques catalyze an emerging field of studying how cells convert from one phenotype to another, in a step-by-step process. Two grand technical challenges, however, impede further development of the field. Fixed cell-based approaches can provide snapshots of high-dimensional expression profiles but have fundamental limits on revealing temporal information, and fluorescence-based live-cell imaging approaches provide temporal information but are technically challenging for multiplex long-term imaging. We first developed a live-cell imaging platform that tracks cellular status change through combining endogenous fluorescent labeling that minimizes perturbation to cell physiology and/or live-cell imaging of high-dimensional cell morphological and texture features. With our platform and an A549 VIM-RFP epithelial-to-mesenchymal transition (EMT) reporter cell line, live-cell trajectories reveal parallel paths of EMT missing from snapshot data due to cell-cell dynamic heterogeneity. Our results emphasize the necessity of extracting dynamical information of phenotypic transitions from multiplex live-cell imaging.