Scientists have created monkeys connected to their mothers by a genetically-altered placenta, according to a report published today in the Proceedings of the National Academy of Sciences. This experiment marks the first time a gene introduced into a primate has remained functioning throughout pregnancy, up to and beyond birth. Such animals will allow researchers to better understand certain problems that can arise during pregnancy.

Thaddeus Golos and colleagues at the University of Wisconsin Medical School injected 14 rhesus monkey embryos with a heavily edited form of HIV carrying the gene for green fluorescent protein (GFP), a jellyfish protein and common lab tool that glows green under fluorescent light. Two of these embryos survived and produced the protein (see image). These animals differ from ANDi, the transgenic monkey born last year, in that they don't carry the GFP gene in their body's cells, but rather in the DNA of their placenta. Also ANDi didn't express the gene he carried. "This is an important distinction," Golos says, "since the success of transgenic or gene transfer studies is determined by whether or not the protein is produced."

This technique will enable researchers to better understand the placenta and its interaction with the pregnant mother. As do other animals, developing monkeys carry genes from their fathers whose products have to be tolerated by their mothers' immune systems. The way a mother's immune system reacts could be an important factor in deciding how smoothly a pregnancy goes, and the placenta most likely plays a key role in softening this response. "This [model] will allow us to explore how the placenta does that," Golos says. "What we can do is explore successful pregnancy in a primate model and, using genetic approaches, modify the way the placenta develops [then] monitor the maternal response."