Dissection of signaling networks regulating stem cell maintenance and asymmetric cell division in developing and adult lung epithelia

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The primary objective of this proposal is a better understanding of the molecular signaling network that determines the balance between self-renewal and differentiation of progenitor cells of endodermally derived lung epithelia. We want to clarify the specific roles of individual components of the notch-signaling pathway for symmetric and asymmetric celi divisions and cellular differentiation and for the generation of stem cells of the lung epithelium, which constitutes a major part of the lung parenchyma. We will also disrupt the Wnt-signalling pathway in defined cell populations of the lung using a newly developed repressive version of ß-catenin, which will actively suppress target genes of the canonical Wnt pathway and analyze the role of the secreted Wnt-inhibitor Wif-1 during lung development and for lung tissue remodeling in adult mice. Another major objective is the visualization and tracing of lung stem cells. To achieve this goal we will utilize a new experimental approach, which is based on DnaE-mediated protein splicing to reconstitute the tet-repressor, and apply an innovative split-cre system to löeniify anä trace lung stem cells, which co-express CC10 and SP-C. The design of the cellular tracing system, which will permanently label specific cell populations, does also allow the unequivocal identification of descendants of labeled (stem) cells. As an alternative approach to identify and manipulate lung stem cells, we will take advantage of a reporter strain, which marks cells that have encountered past or conceive present notch signaling. Finally, we will analyze the role of Oct4 positive cells in the lung by conditionally inactivating Oct4 in the endoderm and in specific cell populations in the lung. The fate of Oct4 positive cells will be traced using a new mouse strain, which carries a conditionally active Cre-recombinase (MerCreMer) inserted into the Oct4 locus. Tracing and manipulation of the lung stem cells and their descendants, with focus on the signaling networks addressed above, will be employed to asses their role in the maintenance of lung homeostasis and in processes of lung injury, repair and regeneration.