Networks of epithelial and endothelial tubes are essential for the function of organs
such as the lung, kidney and vascular system. The sizes and shapes of these tubes
are highly regulated to match their individual functions. Defects in tube size can
cause debilitating diseases such as polycystic kidney disease and ischaemia(1,2).
It is therefore critical to understand how tube dimensions are regulated. Here we
identify the tyrosine kinase Src as an instructive regulator of epithelial-tube length
in the Drosophila tracheal system. Loss-of-function Src42 mutations shorten tracheal
tubes, whereas Src42 overexpression elongates them. Surprisingly, Src42 acts distinctly
from known tube-size pathways and regulates both the amount of apical surface growth
and, with the conserved formin dDaam, the direction of growth. Quantitative three-dimensional
image analysis reveals that Src42- and dDaam-mutant tracheal cells expand more in
the circumferential than the axial dimension, resulting in tubes that are shorter
in length-but larger in diameter-than wild-type tubes. Thus, Src42 and dDaam control
tube dimensions by regulating the direction of anisotropic growth, a mechanism that
has not previously been described.
