Shaping Up

Ephemeral soap bubbles give clue to how cells develop with regular shapes in tissues


Tracking each cell in a growing zebra fish allows researchers to tease out patterns in cell shape and cell division orientation from the chaos of development. Image: Megason lab.Biological development is a chaotic affair.

Developing cells come in all sorts of shapes. They may be flat as a pancake, equilateral like a cube or long and skinny like a hose. Developing embryos arise from eggs of different sizes, and they often grow within dynamic environments. Thanks to sexual reproduction and random mutation, they have a variety of genetic signatures. To top it all off, the genetic circuits within the cells are known to be noisy and prone to error. Yet somehow, despite all this chaos, most animals are born perfectly normal.

“Given this unavoidable noise, how can development give rise to organisms that are so precisely patterned and organized?” said Sean Megason, associate professor of systems biology at Harvard Medical School. “We think the general answer is that there are feedback systems at many levels that monitor the progress of developing tissues and make course corrections along the way to stay on track despite the inevitable variations.”

Think of a biological thermostat, turning on the air conditioning when it gets too hot or the heat when it gets too cold, but instead of maintaining a comfortable room temperature, these feedback loops keep tissues developing smoothly and bodies growing with bilateral symmetry.

In a study reported in the current issue of Cell, Megason and colleagues in the HMS systems biology department and the mathematics department at Susquehanna University, Selinsgrove, Pennsylvania, focused on the question of how the correct three-dimensional shape of cells is produced in an epithelial tissue on the zebra fish embryonic surface called the presumptive enveloping layer (pre-EVL).

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