Figure 1. A whole-mount preparation of a mammary gland from a mouse in midpuberty. The ductal tree originates at the nipple (N) and displays many terminal end buds (large arrow) and lateral buds (small arrows). ×5.

Figure 2. Branching morphogenesis of the developing rat lung in culture. Embryonic rat lung isolated at gestation day 13.5 (equivalent to day 11.5 gestation mouse) is shown after 1 (a), 3 (b) and 5 (c) days in culture. Extensive branching of the epithelial tubules take place in vitro. tr, trachea; pl, proximal lung; dl, distal lung. All pictures were taken under same magnification.

Figure 3. Epithelial-mesenchymal interactions regulate the pattern of branching of the developing lung. Diagram illustrates the basic architecture of the mouse/rat embryonic lung at the time of isolation for culture. The left lung (LL) has a single lobe, while the right lung (RL) is divided into cranial (cr), medial (m), accessory (a) and caudal (ca) lobes. Representative signalling molecules expressed in the developing lung are depicted. Epithelial Shh has its receptor patched (Ptc-1) and other target genes in the mesenchyme. Mesenchymal FGF-10 binds to FGFR-2 expressed in the epithelium. The transcription factors TTF-1 and Hox are found in the epithelium and mesenchyme, respectively.

Figure 4. Branching morphogenesis of mouse embryonic submandibular gland. (a) A gland with a round lobule corresponding to mid 12-day stage. (b) A gland of very late 12-day stage with one narrow cleft (black arrow) and two small indentations (white arrows), one of which will become a definite cleft at early 13-day stage. (c) An early 13-day gland having three lobules separated by two narrow, deep clefts. (d) A mid to late 13-day gland having four lobules separated by three clefts. Asterisk indicates sublingual epithelium. After Nakanishi Y and Ishii T. Epithelial shape change in mouse embryonic submandibular gland: modulation by extracellular matrix components. BioEssays 11: 163–167. Copyright © 1989 by Wiley-Liss, Inc., a subsidiary of John Wiley & Sons, Inc. All rights reserved.

Figure 5. Simulation of lung development by a mechanical model where tissues are considered to behave as fluids of different viscosities and surface tensions. Curves represent epithelial boundary over time. Tissues in model are constrained by boundaries on two sides, but are free to expand on the third side. The physical parameters of the model are consistent with length and time scales of embryonic lung, and tissue viscosity and surface tension are estimated from in vitro experiments. After Lubkin AR and Murray JD. A mechanism for early branching in lung morphogenesis. Journal of Mathematical Biology 34: 77–94. Copyright © 1995 by Springer Verlag. All rights reserved.