In an important proof-of-concept experiment that paves the way for more direct analysis of primate biology, researchers at Oregon Health Sciences University (OHSU; Beaverton, OR) have generated transgenic rhesus monkeys. Though only one monkey carrying the GFP transgene survived past birth, two miscarried fraternal twins expressed the fluorescent protein in all tissues that were examined. The surviving transgenic monkey, named ANDi (for inserted DNA, in reverse-transcribed orientation), does not yet express the GFP protein, but carries the gene. Gerald Schatten, senior author on the paper, explains that the team overcame several difficulties in order to produce ANDi: “Without a litter, and with limited eggs and surrogates, approaches that have acceptable success rates in mice may be too low to be useful in primates. Also, primate embryos implant best if transferred at the 4 to 8 cell stage of development, precluding selection at the blastocyst stage.” The scientists adapted retroviral vector techniques that were previously used to produce transgenic cattle, but the success rate of the procedure is still quite low. 224 monkey oocytes were injected and fertilized in order to produce ANDi. The researchers, whose work appears in Science (291, 309, 2001), now hope to develop additional techniques for generating transgenic monkeys, including targeted gene disruption and the use of primate ES cells.