Inhibitory morphogens and monopodial branching of the embryonic chicken lung

Abstract

Branching morphogenesis generates a diverse array of epithelial patterns, including dichotomous and monopodial geometries. Dichotomous branching can be instructed by concentration gradients of epithelial-derived inhibitory morphogens, including transforming growth factor-β (TGFβ), which is responsible for ramification of the pubertal mammary gland. Here, we investigated the role of autocrine inhibitory morphogens in monopodial branching morphogenesis of the embryonic chicken lung. Computational modeling and experiments using cultured organ explants each separately revealed that monopodial branching patterns cannot be specified by a single epithelial-derived autocrine morphogen gradient. Instead, signaling via TGFβ1 and bone morphogenetic protein-4 (BMP4) differentially affect the rates of branching and growth of the airways. Allometric analysis revealed that development of the epithelial tree obeys power-law dynamics; TGFβ1 and BMP4 have distinct but reversible effects on the scaling coefficient of the power law. These data suggest that although autocrine inhibition cannot specify monopodial branching, inhibitory morphogens define the dynamics of lung morphogenesis.

Apical constriction initiates new bud formation during monopodial branching of the embryonic chicken lung

“…Embryonic lungs were dissected using a pair of forceps in cold PBS supplemented with antibiotics (50 units/ml of penicillin and streptomycin; Invitrogen). Dissected lungs were cultured over a porous membrane (nucleopore polycarbonate track-etch membrane, 8 µm, 25 mm; Whatman) in DMEM/F12 medium (without HEPES) supplemented with 5% fetal bovine serum (FBS, heat inactivated; Atlanta Biologicals) and antibiotics (50 units/ml each of penicillin and streptomycin) (Miura et al, 2009;Gleghorn et al, 2012). To alter the rate of proliferation, we varied the concentration of FBS in the culture medium; these treatments had no effect on the relative pattern of proliferation.…”

The control of branching morphogenesis

“…When 3D shapes of lung bud epithelia were used in a simulation, that had been extracted from early developing chicken lungs, simulated secretion of a ligand from the epithelium into a large computational bounding box (that would model the mesenchyme) resulted in a steady-state concentration pattern that approximately coincided with where the authors would expect branching of secondary bronchi to be inhibited (Fig. 10b,c) [57].…”

Quantitative approaches to uncover physical mechanisms of tissue morphogenesis

“…As evidenced in vivo [4–7] and in two-dimensional (2D) and three-dimensional (3D) engineered culture models [8–12], tissue geometry sculpts patterns of soluble factors and mechanical forces that in turn feed back to generate spatial patterns of cell behavior and further drive tissue form and remodeling. To begin to understand the complex and non-intuitive behaviors that emerge in multicellular systems, a fundamental question must be answered: how do the cells within these tissues move over time?…”