Order in the lung

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Abstract
Given the lung's thousands of branching airways, its development might be expected to be a highly complex process. Yet a surprisingly simple picture now emerges of when, where and in what order these branches form. How the massively branched networks of the lung and other organs are generated during development and how the patterning information is encoded have long fascinated biologists and mathematicians. Now the complete branching pattern and branch lineage of the mouse bronchial tree has been determined from an analysis of hundreds of developmental intermediates. The process is remarkably stereotyped and mathematically elegant. The entire tree is generated from three geometrically simple local branching modes used in three different orders. Development proceeds in the manner of a computer program with each mode of branching controlled by a genetically encoded subroutine in a series of local patterning and morphogenesis operations, which are themselves controlled by a more global master routine.