Avian species comparisons and cell shape changes in the developing lung

Abstract

It has recently been shown that the secondary bronchi, or the new branches, of the domestic chicken lung form by apical constriction, as epithelial cells in the primary bronchus narrow on the inner side of epithelial wall, forming trapezoid-like prisms. These new branches form at nearly exact locations along the primary bronchus when comparing it to the length of the primary bronchus. In cultured lung explants, domestic chicken, Japanese quail, and pekin duck lungs also exhibit stereotyped bud location after 48 hours of culture. This thesis examines how the in vivo model of these three avian species relate in terms of formation and location of secondary bronchi. Through HH staging analysis, the three species exhibit different time scales of development. Data agree that the location of secondary bronchi is pre-determined, but all ratios decrease significantly as HH stage increases. Secondary bronchi form at nearly the same positions in domestic chicken and Japanese quail, which matches evolutionary relationships, whereas secondary bronchi form at different positions in the pekin duck. The length of the primary bronchus likewise increases with increasing HH stage, which helps uncover a potential model for how the lungs of these three avian species develop over the course of each HH stage. Fluorescence microscopy analysis of lung samples at early stages determine that each secondary bronchus forms via apical constriction of the dorsal epithelium of the primary bronchus. Research that seeks to further understand lung branching and lung development will contribute to novel treatments for developmental and severe lung diseases and open the door to techniques in regenerative medicine.