Mammalian Embryo: Branching Morphogenesis


Branched structures are common in mammals and exist mainly to solve problems of transport. Branched architectures allow a surface area to be packed into a small volume, minimize the distance of cells from transport systems and from the entrance of a system to its end. For development and evolution, branched structures offer the advantage of being scaleable: tree‐shaped systems can grow and add branches without altering their basic nature. Branching morphogenesis takes place by four methods: fusion, clefting, sprouting and intussusception. All are controlled by paracrine factors and take place through changes in the behaviours of cytoskeleton‐adhesion systems.

Key concepts:

  • The internal anatomy of mammals involves many branched structures.

  • Branched architectures optimize transport in compact organisms.

  • Branched architectures can be scaleable, which has evolutionary and developmental implications.

  • Branching can be by fusion, clefting, sprouting and intussusception.

  • The largest branches tend to be stereotypical and under precise genetic control, but the finest ones are pseudo‐fractal and quite variable.

  • Branching depends on ramogenic signals from surrounding cells.

  • Branching structures have endogenous mechanisms to ensure appropriate spacing; at least some rely on repulsive autocrine cues.

Keywords: sprouting; fusion; intusussception; branching; fusion; organogenesis

Figure 1.

The four main types of branching. The significance of the label ‘collagen’ will be explained in the section on cellular mechanisms of branching.

Figure 2.

The possible role of actin–myosin contraction in making new sprouts. (a) The ureteric bud, the progenitor of the urinary collecting duct system of the kidney, branching from the Wollfian duct. It has been stained with phalloidin, which identifies actin filaments: they are particularly prominent in the concave surfaces of epithelial cells in the branch ends that are sprouting out. (b) The proposed mechanism in cartoon form. Micrograph credit: Michael L and Davies JA, not previously published.



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Davies, Jamie A(Sep 2009) Mammalian Embryo: Branching Morphogenesis. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0000741]