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Thinner tubes

Paired cells intercalate (top) as visualized via labeling of adherens junctions (bottom). AFFOLTER/ELSEVIER

A switch that controls cell intercalation determines the diameter of fly embryo tracheal tubes, according to Carlos Ribeiro, Marc Neumann, and Markus Affolter (Biozentrum, Universität Basel, Switzerland). Other tube-like structures such as blood vessels may use similar sculpting techniques.

The direction of tracheal tube extension is defined by migration of interconnected precursors toward an FGF signal. But tube morphology is also affected by Dpp and Wnt signaling. The Swiss team wanted to know what cellular processes were being controlled by Dpp and Wnt.

They made movies of living fly embryos with labeled adherens junctions (AJs). The label showed cells that were initially paired, side-by-side, in wider tubes. But gradually individual cells reached around at one end until they made contact with themselves, and then started replacing their intercellular AJs with autocellular AJs. This squeezing process continued until the tube was longer but only one cell circumference around.

Expression of the Wnt target Spalt, a transcription factor, was necessary and sufficient to prevent this intercalation process in tubes that remained larger. Dpp's normal function, by contrast, is to repress Spalt expression and thus allow intercalation.

Cells formed autocellular AJs as long as they had a Spalt-free neighbor. So perhaps it is contraction by the neighbor rather than outgrowth by the autocellular AJ-forming cell that is the driving force. Affolter plans to label old and new AJs to help him determine which cell is controlling the process and whether cell sliding, rolling, or detachment are involved in the reassortment of junctional contacts.

Reference:

Ribeiro, C., et al. 2004. Curr. Biol. 14:2197–2207.[CrossRef][Medline]

William A. Wells

wellsw{at}rockefeller.edu

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This Article Full Text (PDF, 426K) PPT slides of all figures Alert me when this article is cited Services Email this article Similar articles in this journal Alert me to new content in the JCB Download to citation manager Citing Articles Citing Articles via CrossRef Citing Articles via Google Scholar Google Scholar Articles by Wells, W. A. Search for Related Content PubMed Articles by Wells, W. A. Social Bookmarking                            What's this?