Non-human primates are valuable for modelling human disorders and for developing therapeutic strategies; however, little work has been reported in establishing transgenic non-human primate models of human diseases. Huntington's disease (HD) is an autosomal dominant neurodegenerative disorder characterized by motor impairment, cognitive deterioration and psychiatric disturbances followed by death within 10-15 years of the onset of the symptoms (1-4). HD is caused by the expansion of cytosine-adenine-guanine (CAG, translated into glutamine) trinucleotide repeats in the first exon of the human huntingtin (HTT) gene (5). Mutant HTT with expanded polyglutamine (polyQ) is widely expressed in the brain and peripheral tissues (2,6), but causes selective neurodegeneration that is most prominent in the striatum and cortex of the brain. Although rodent models of HD have been developed, these models do not satisfactorily parallel the brain changes and behavioural features observed in HD patients. Because of the close physiological (7), neurological and genetic similarities (8,9) between humans and higher primates, monkeys can serve as very useful models for understanding human physiology and diseases (10,11). Here we report our progress in developing a transgenic model of HD in a rhesus macaque that expresses polyglutamine-expanded HTT. Hallmark features of HD, including nuclear inclusions and neuropil aggregates, were observed in the brains of the HD transgenic monkeys. Additionally, the transgenic monkeys showed important clinical features of HD, including dystonia and chorea. A transgenic HD monkey model may open the way to understanding the underlying biology of HD better, and to the development of potential therapies. Moreover, our data suggest that it will be feasible to generate valuable nonhuman primate models of HD and possibly other human genetic diseases.
We injected 130 mature rhesus oocytes with high titre lentiviruses expressing exon 1 of the human HTT gene with 84 CAG repeats (HTT-84Q; Fig. 1c) and lentiviruses expressing the green fluorescent protein (GFP) gene (Fig. 1c), under the control of the human poly-ubiquitin-C promoter, into the perivitelline space. After fertilization by intracytoplasmic sperm injection, 82% (89 out of 108) of the zygotes developed to the 4-8-cell stage and 30 embryos were transferred to eight surrogates. Of those surrogates, six pregnancies (75%; 6 out of 8) were established and five live newborns (22%, 5 out of 23; rHD-1, rHD-2, rHD-3, rHD-4 and rHD-5) were delivered at full term (Table 1). Among these five newborns, two sets of twins (rHD-1 and rHD-2; rHD-4 and rHD-5) were delivered by caesarean section, and a singleton (rHD-3) was delivered naturally.
All of the transgenic monkeys carried the transgenic mutant HTT and GFP genes. Fig. 1 shows two monkeys (rHD-1 and rHD-2, fraternal twins; Fig. la) expressing GFP at 4 weeks of age (Fig. lb). Transgene integration was confirmed by polymerase chain reaction (PCR) (Fig. l d, e) and Southern blot analysis (Supplementary Fig. 1). We estimated that rHD-1 and rHD-2 carried a mutant HTT gene in samples of umbilical cord, whereas placental tissue of extraembryonic origin from rHD-1 had two mutant HTT genes of different size (Fig. ld). Two or more integration sites were...