Nuclear transfer in the rhesus monkey: Practical and basic implications

In early 1997, the birth of a lamb after transfer of the nucleus from an ad ult mammary gland cell into an enucleated oocyte, along with the production of rhesus monkeys by nuclear transfer of embryonic cells, marked a reemerg ence of the field of mammalian cloning. Clonally derived rhesus monkeys wou ld be invaluable in biomedical research, and the commercial interests in tr ansgenic sheep and cattle propagated by cloning are substantial, Nuclear tr ansfer technology is under consideration in human in vitro fertilization cl inics to overcome infertility secondary to advanced maternal age or mitocho ndrial-based genetic disease. Nuclear transfer involves preparing a cytopla st as a recipient cell, in most cases a mature metaphase II oocyte from whi ch the chromosomes have been removed. A donor nucleus cell is then placed b etween the zona and the cytoplast, and fusion, as well as cytoplast activat ion, is initiated by electrical stimulation, Successful reprogramming of th e donor cell nucleus by the cytoplast is critical-a step that may be influe nced by cell cycle stage, Embryos produced by nuclear transfer are cultured in vitro for several cell divisions before cryopreservation or transfer to the oviduct or uterus of a host mother. The efficiency of producing live y oung by nuclear transfer in domestic species is low, with a high frequency of developmental abnormalities in both preterm and term animals. However, a number of pregnancies have now been established using fetal cells as the s ource of donor nuclei, The use of cell lines not only allows large clone si zes but also supports the ability to genetically manipulate cells in vitro before nuclear transfer, Ongoing research focused on the production of clon ally derived rhesus monkeys using fetal fibroblasts and embryonic stem cell s as the source of donor nuclei will be reviewed.