hogge@m2.csc.ti.com (John Hogge) (10/17/89)
Question: many years ago I heard about successful cloning of mice, but I've got a bet to resolve--has anyone successfully cloned cattle? If so, is their commercial practice? Please respond direct to me--I don't read this. Thanks, --John HOGGE@CSC.TI.COM
overt@prc.unisys.com (Christian Overton) (10/21/89)
In article <94761@ti-csl.csc.ti.com>, hogge@m2 (John Hogge) writes: >Question: many years ago I heard about successful cloning of mice, but I've >got a bet to resolve--has anyone successfully cloned cattle? If so, is >their commercial practice? > >Please respond direct to me--I don't read this. >Thanks, >--John HOGGE@CSC.TI.COM The reported cloning of mice turned out to be one of the more interesting cases of scientific fraud during the late 70s, early 80s. Dr. Karl Illmensee (who, at the time, was a professor at Zurich, Geneva or Basel, I forget which one) claimed to have produced viable adult mice by nuclear transplantation of either embryonal carcinoma cells and, I believe, 1- or 2- cell stage nuclei into enucleated zygotes. He first announced limited success in nuclear transplantation experiments about 1979 and labs around the world tried for the next 5 years to duplicate his increasingly more dramatic results in a variety of organisms, including sheep and rabbits, without success. Eventually (circa 1984), one of his own post-docs caught him switching mice and turned him. You might wonder how Illmensee could get away with such claims for so long. He had previously demonstrated his scientific competence by doing transplantation experiements in Drosophila that showed that syncytial nuclei were equivalent and totipotent, and other widely acclaimed experiments with Anthony Mahowald that showed that cytoplasm from the Drosophila pole plasm determined the developmental fate of the nuclei. These experiments have all been confirmed independently. Before moving on to Switzerland, Illmensee worked with B. Mintz on mouse embryonal carcinoma cells (equivalently teratocarcinoma stem cells) where again he did outstanding work involving micro-injection experiments on embryonic tissue. So when he claimed that he could clone mice by nuclear transplantation, everyone was ready to believe him (after all frogs had been cloned by nuclear transplantation of somatic cells nearly 20 years before by John Gurdon and others), and when no one could duplicate the experiments right away, it was assumed that Illmensee was either had better hands than anyone else -- a real possibility because the technique requires substantial talent -- or he was holding back on some essential trick like how he treated his water, or pulled his micro-pipettes or something equally arcane. At the time, one of my lab-mates, Jim McGrath, had been trying to duplicate the experiment for 3 years when Illmensee made a visit to the lab and told Jim that he would show him exactly the experimental protocol. Everything was set up -- the pipettes pulled, the water prepared just right, the critical reagents made under Illmensee's watchful eye -- and just as they were about to begin the experiment, Illmensee's wife called and said he had to go shopping with her, and off he went never to return. Shortly thereafter, Jim abandon the micro-injection approach in favor of sendai virus fusion experiments. He quickly showed, in contrast to Illmensee's results, that even the nucleus from a 2-cell stage embryo could not support development to term. Jim wrote this up and submitted it to a prestigious journal which naturally rejected it because Illmensee had already shown that he could clone to term. Of course, this journal's responsiveness to Jim's work changed dramatically after Illmensee was discredited. Jim's initial work was been pursued by many others in the following years and has had a major impact on our understanding of the maternal and paternal genetic contribution: the bottom line here is that while the DNA sequences contributed maternally and paternally are essentially equivalent in mammals, the genetic contribution is different due to "masking" of the expression of a small subset of the genes. For development to proceed normally requires a haploid complement prepared by spermatogenesis and a haploid complement prepared by oogenesis. What this means is that mammals CANNOT be cloned from somatic cells and maybe not at all. The only possible out is that clones might be produced by blastoderm injection of embryonal carcinoma cells, or their normal equivalents, accompanied by the complete removal of the host inner cell mass. As has been known for the last 15 years or so, if the host inner cell mass is not removed then a chimeric organism will be produced. So, if anyone wants to volunteer to have a testicular or ovarian teratoma generated from which embryonal carcinoma cells can be derived, then there is a remote possibility in the distant future that you could be cloned. -- +--------------------------------------------------------------------+ | G. Christian Overton, Staff Sci. || Telephone: (215) 648-7533 | Unisys Paoli Resarch Center || Internet: overt@prc.unisys.com | P.O.Box 517 || FAX: (215) 648-7390