Stem cells have the ability to transform into any type of cell in the body, from liver to eyeball to bone marrow. How the cells of the body know what to turn into has long been one of biology's deep mysteries. But scientists now have a pretty good idea of how to give the cells instructions in the lab. But as recently minted Ph.D. Christopher Bissonnette will tell you, the process is inexact, time-consuming, tedious, maddening and, occasionally, hugely rewarding.
Bissonnette toiled for some six years in a cramped little lab at Northwestern University’s Feinberg School of Medicine. Earlier this month, he and his colleagues revealed the fruits of their labor: neurons made to order. Specifically, the kind of neurons that are among the first to go in Alzheimer's Disease. So how do you turn stem cells, these blank slates, into just one of the more than 200 cell types that make up the human body?
According to Bissonnette, the answer, at least at first, is to essentially mimic the conditions the cells experience in the womb. That means, first of all, keeping them well fed in their little petri dishes. These ain't your goldfish – you can't skip a day and then double the food later. They're so demanding that after a bike accident broke two bones in Bissonnette's wrist, he went in to feed his cells before hitting the ER.
The cells are then soaked in various growth factors, which are solutions that contain different proteins, for very specific amounts of time. This is supposed to approximate the chemical environment of a developing brain. Trouble is, you rarely know going in exactly which factors to use when and for how long. So Bissonnette tried a little of this, a little of that. Toward the end of each six-week growth cycle he'd check to see what he had. At first, it was a salad of dozens of different kinds of brain cells,. Then trial after meticulous trial, he refined the process over the course of years. He went from getting a handful of the kinds of neurons he wanted to a majority … and finally, to dishes made almost entirely of the beautiful, long-tailed, technicolor-stained cells he was after.
Now Bissonnette's work has been taken up by colleagues, who are refining a process that can make the cells without using embryonic stem cells (though it's worth noting that the original experiments all used federally approved cell lines). They take skin cells, convert them first into stem cells, and then into the proper neurons. The hope is, eventually, that scientists could grow new neurons from an Alzheimer's patient's own cells, which could replenish the ones that have died in the brain.
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