Fluid for a single lumen

All biological tubes consist of a single lumen. According to Michel Bagnat, Didier Stainier, and colleagues (University of California, San Francisco, CA), one way to ensure this singularity is to use fluid pressure.

Too many lumens are found in the gut of Zebrafish larvae lacking the Tcf2 transcription factor. Extra tubes remain because they fail to coalesce normally during development. Bagnat and colleagues guessed that coalescence might be controlled by genes under Tcf2's control.

DNA microarrays revealed that the gene for an epithelial junction protein, called claudin 15, was down-regulated in tcf2 mutants. Claudins form pores between cells that allow ions to be transported across epithelia down an electrochemical gradient. Tcf2 mutant gut cells also lacked a Na⁺/K⁺ ATPase, which probably creates the gradient that drives ions through the pores....