First rats cloned

Animal models for human disease play an important role in understanding the causes and mechanisms of genetic disorders and are invaluable in developing new treatments and therapeutics. These animals are produced by several techniques, including transgene insertion and targeted gene knockout in embryos to generate new lines, but the subsequent crossbreeding and necessary genotyping make these time-consuming strategies. The generation of embryonic stem cell lines from genetically engineered embryos combined with somatic cell nuclear transfer (SCNT) is routinely used to produce animal clones with a known genotype from which further stocks can be bred and has been used with success in the production of sheep and mice. However, the production of cloned rats has been unsuccessful due to technical difficulties associated with spontaneous oocyte activation that occurs within an hour of egg collection.In the September 25 Science, Qi Zhou and colleagues in a collaboration among Institut National de la Recherche Agronomique, the Chinese Academy of Sciences, and the biotech company genOway report the first successful production of cloned rats using a technique that reversibly blocks meiotic metaphase–anaphase transition in the oocyte and allows the successful uptake of transferred somatic cell nuclei (Science, DOI:10.1126/science.1088313, September 25, 2003). "It is a real scientific collaboration between an academic group headed by J.P. Renard and a biotech company team," Alexandre Fraichard, chief executive officer of genOway, told The Scientist by E-mail. "Both partners provided expertise and technologies."The team reported earlier attempts to develop a rapid, single-step, nuclear transfer technique, but found that within 30 minutes of collection, 70% of oocytes showed evidence of maturation. And while 201 out of 221 apparently successfully cloned embryos divided into two-cell embryos, no fetal development was observed in any of them. "It is very difficult since the oocytes start their development as of collection. This was the bottleneck of the technique," explained Fraichard. "We solved it by using an inhibitor [MG132] of the molecular pathway responsible for oocyte development." Despite the use of the oocyte activation blocker in the culture medium, the technique nevertheless demanded that the procedure was completed swiftly. Eight hundred seventy-six embryos generated by SCNT within 30 minutes of removal of the processed oocytes from culture in MG132 were replaced in 12 female recipients and developed into fetuses. Subsequently, 129 cloned embryos were replaced in two female recipients, one of which delivered three live male pups that were confirmed to be genuine clones by microsatellite analysis.According to Fraichard, it was necessary to replace this number of embryos in a single female recipient. "It has been shown in the pig that it could facilitate late embryonic development. It is not the cause of the success but it can have increased our final efficiency. It is very likely that it is not affecting embryo transfer, and is coherent with the [success] rate obtained in other species."Zhou et al. also report the further successful generation of two female rat clones, both of which are fertile and produce normal offspring. "The success we have announced today represents an important result for the pharmaceutical industry, as bio-pharmaceutical companies can now look forward to significant productivity increases in their R&D process by using genetically modified rats," Fraichard said in a press release. "This would save tremendous resources in the industry by optimizing management of the drug development pipeline. We are currently working on building an international consortium that would bring together pharmaceutical companies and biotech companies with the objective of developing knock-out and knock-in rat models targeting therapeutic areas of high unmet medical need, such as hypertension, obesity, diabetes and neurological disorders."

First rats cloned

Successful cloning of laboratory rats offers new opportunities for disease research and drug discovery

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