Developmental biology: order in the lung

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.

Figure 1. A master and three slaves

Studying early lung morphogenesis in the mouse embryo, Metzger et al. show that this organ’s airways form in a sequential manner in three series of events, or subroutines, which are all driven by one master branch generator. a, At embryonic day (E) 10.5, the primary bronchial branch (1) forms, followed by (b) the development of the left upper-lobe branch (2) by E11. c, The first two segmental branches of the left upper-lobe branch (2.2 and 2.3) and the subsequent formation of branches 3–6 occur at E12. The master branch generator is active throughout these events, and the inferred sites of action of the periodicity clock and bifurcator subroutines are shown. At E12, the rotator subroutine has not yet begun to function.