Many organs contain tubular epithelia, and their development involves tubule elongation, lumen formation, and establishment and maintenance of tubular integrity. Yuji Atsuta and Yoshiko Takahashi (p. ) investigate how these processes are coordinated, using the chicken Wolffian (or nephric) duct (WD) as a model. The WD extends posteriorly from the pronephric region, between the presomitic mesoderm (PSM) and the lateral plate mesoderm. Cells at the front of the extending tissue show mesenchymal characteristics, while towards the rear, WD cells become more epithelial and the tubule lumen forms. Here, the authors find that WD migration is driven by a dynamic FGF gradient: FGF8 is expressed in the extending PSM and serves as a chemoattractant for the leading WD cells. Where FGF concentrations are low anteriorly in the segmented somites, the rear part of the WD epithelialises. Thus, as the body axis extends and the FGF source moves more posteriorly, the WD tube forms progressively, in a manner coordinated with whole-body elongation.
