Chemical and Neural Regulation of Embryonic Branching Morphogenesis

Citation

Bower, Danielle Vera Brown (2013) Chemical and Neural Regulation of Embryonic Branching Morphogenesis. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/Z9SX6B6R. https://resolver.caltech.edu/CaltechTHESIS:05302013-135915010

Abstract

Lung development is a complex process orchestrated by as many as 40 different types of cells and many signaling and regulatory factors. The spatial sequence of branching of bronchial epithelial tubes is stereotyped. However, it remains unknown how the timing of branch formation is encoded and whether this branching clock function is unique for different tissue types or is conserved across species and lineages that undergo iterative branching. Investigations of the function of the sarcoplasmic-endoplasmic reticulum calcium ATP-ase (SERCA) reveal that protein kinase C (PKC)-modulated SERCA activity controls branch formation across tissues and species.

SERCA controls the rate of intersomitic blood vessel sprouting and branching in zebrafish embryos in a dose-dependent manner. Vessel sprouting recovers upon removal of inhibition and restoration of pump activity. Regulation of cell motility is responsible for these effects.

Similarly, during Drosophila embryonic development, SERCA activity is required for the proper formation of both the central nervous system axon tracts and the network of tracheal tubules that deliver oxygen to tissues. SERCA blockade results in breaks in the tracheal structure and displaced axons. Removal of inhibitor partially rescues these defects, while simultaneous treatment with both SERCA inhibitor and PKC activator remarkably rescues tracheal and neural development. Dynamic imaging of Drosophila embryonic tracheal morphogenesis demonstrates that SERCA's principal function is to govern cell migration. Together, these finding reveal that SERCA regulates cell migration, and this serves as a conserved mechanism that governs branch formation in various cell types and species during development.

On the other hand, morphogens and cell-cell interactions are critical to form a complex, specialized organ such as the mammalian lung. Nerves are known to be present from the early stages of lung branching. Yet a role for nerves in modulating epithelial branching remains to be discerned. Denervation of embryonic mouse lung explants reveals that lung branching requires nerves. Targeted neural ablation, but not inhibition of acetylcholine receptors, halts lung branching and causes a reduction in endothelial cells and epithelial and mesenchymal proliferation. Likewise, ablation of nerves in Drosophila embryos derails tracheal morphogenesis. Therefore, nerves play a conserved role in directing epithelial airway branching.

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