Branching Morphogenesis and Epithelial Fusion in Embryonic Development of Avian Lungs

Abstract

Little is known about the program of branching morphogenesis in embryonic chicken lungs, particularly with regards to the role that various molecules in the lung environment might play in directing branching, growth, and fusion. A better understanding of how branching morphogenesis is controlled is extremely important to the field of lung tissue engineering, which is a possible future way to improve the standard of treatment for lung diseases. Characterization of the program of development of chicken lungs also has important evolutionary implications, as avian lungs differ drastically from mammalian lungs, featuring several differences that enable far greater gas exchange efficiency in birds. This study characterizes the program of branching, growth, and fusion via an immunostaining and epifluorescent imaging approach, achieving a large improvement in image quality over any previous work exploring lung development in chickens. In particular, the study focuses on an area at which opposing sets of parabronchi approach each other, interweave, and exhibit profuse anastomosis at Day 11-12 of development. This growth is quantified and supports the possibility that a reaction-diffusion model may be a potential control mechanism for growth and fusion in this lung geometry. Furthermore, the study assesses the usefulness of two candidate open window procedures for the sake of providing a viable way to manipulate molecules in the lung environment in ovo to understand their function. Initial results from one of them, the Minimal Invasion procedure, suggest that it may be an effective way to successfully elucidate the role of a variety of molecules associated with epithelial growth. Finally, immunostains for β-catenin, DAPI, vimentin, and Slug are carried out, and Slug is identified as a target molecule for manipulation in future open window trials due to its pattern of higher concentration between opposing parabronchi directly prior to fusion.