By Natalie DeWitt and Monya Baker
Monkey embryonic stem cells have, for the first time, been created through somatic cell nuclear transfer (SCNT). All attempts to make human embryonic stem cells through nuclear transfer so far have failed, but Jamie Thomson got the recipe for human embryonic stem cells by first doing so in monkeys, so researchers will likely be going to Shoukhrat Mitalipov of Oregon National Primate Research Center for advice. Mitalipov made his announcement Monday at the International Society for Stem Cell Research in Cairns, Australia, in a special add-on presentation . This finding represents a proof of principle that therapeutic cloning to create patient-specific ES cell lines could work in primates.
Mitalipov and his colleagues used a classic nuclear transfer procedure, where a somatic cell nucleus (in this case form a skin biopsy from a ten year old adult rhesus monkey), was inserted into an enucleated egg. The egg was prodded to start dividing, and developed into a blastocyst (a hollow ball consisting of a few hundred cells). Then Mitalipov teased out the cells of the inner cell mass, a thickening in the ball that would have eventually formed the embryo proper if left undisturbed. Once they placed the cells into a culture dish, the cells began to divide, forming the world’s first cloned primate ES cells.
The Oregon scientists isolated two separate monkey ES cell lines from 20 blastocysts, and went on to show that the ES cells showed the genetic hallmarks of a true cloned cell line, containing the mitochondrial DNA of the egg and the nuclear DNA of the somatic donor cell (which in this case was a male, making it easier to rule out the possibility that it was a parthenote.) The cells behaved like ES cells are supposed to do– self renewing, differentiating into cardiac and neuronal lineages in vitro, and forming teratomas after injection into mice testes.
Mitalipov attributes his success to avoiding the use of a DNA stain to visualize the nucleus of the oocyte during its removal. Instead he combined microscopy with a visualization software that allowed him to see and remove the nucleus. The presumption is that this technique leaves some reprogramming factors in the egg undamaged, allowing them to transform the nucleus of a specialized cell.
“This is the first time this has been done in primates. It’s something we’ve been looking for,” said Alan Trounson of Monash University, adding that the data have not yet been published and the work not replicated and advising due caution.
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