Branching Morphogenesis

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If a picture is worth a thousand words, then a movie is worth a thousand pictures, right?
What is this video of exactly?  This elegant work comes from the lab of Frank Costantini and colleagues at Columbia University, who developed a transgenic mouse line which expressed green fluorescent protein (GFP) under the control of the Hoxb7 promoter, leading to expression of GFP in the ureteric bud & developing collecting system, but not the surrounding mesenchyme which will give rise to the glomeruli and proximal nephrons.  They are able to grow the kidney as a tissue explant–that is, they surgically remove the kidney and grow it in a dish so they can closely examine its development. 
I have included it to illustrate the principle of branching morphogenesis:  a developmental program that is responsible for the highly branched collecting system of the mammalian kidney, which in the human kidney can ultimately will contain hundreds of thousands of nephrons.  How does the ureteric bud know when to start branching?  How does it know when to STOP branching?  What decisions control which cells get to branch and which one stay behind to form, say, the calices as opposed to the collecting ducts?  This model enables these researchers to ask cool developmental biology questions such as this.  This work has broad relevance to developmental biologists, and not just those interested in the kidney–other epithelial tissues such as the lung, breast, and salivary glands for instance appear to use a similar program of branching morphogenesis.  

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