In 2003, Leone and a group of collaborators discovered that loss of the Rb gene caused abnormalities in the placenta, especially where it contacts the uterus. They published that research in the journal Nature.
"This was the first evidence that Rb had an important role in the placenta," says Pamela Wenzel, a graduate student in Leone's laboratory and first author of the new paper.
For this study, Wenzel developed a transgenic mouse that makes an enzyme that deletes DNA. Specifically, it removes the DNA that lies between two gene markers. She then used a second transgenic mouse in which the gene markers were placed in the Rb gene.
When she crossed the two strains of mice, the resulting embryos had the DNA-destroying enzyme and the gene markers in their placenta stem cells. The enzyme removed the DNA between the two markers, leaving the embryos without a working Rb gene in the placental progenitor cells.
These stem cells divided far too often. They gave rise to too many cells and formed a defective placenta, especially where the placenta interacts with the uterus.
These embryos died about 15 days after fertilization, a time at which placenta function becomes critical for survival (the gestation period for mice is 19 days).
Interestingly, the researchers also produced some mice in which the Rb gene was present in the placenta stem cells but destroyed in cells produced by them. These cells formed a normal-looking placenta and the embryos survived.
"This suggests that Rb is important in maintaining placental stems cells, and that it plays a smaller or different role in the cells they give rise to," Leone says.
Lastly, the researchers produced transgenic mice that lacked both the Rb gene and a second gene, E2f3. The Rb protein normally couples with, or binds to, the protein encoded by the E2f3 gene. Embryos miss
Source:Ohio State University