“Epigenetics, then, may be a (co)determinant of the one-celled embryo’s phenotypic profile, but it is not the primary determinant of its ontological status tout court.”
In his response to my argument that Altered Nuclear Transfer (ANT) is a form of human cloning, Father Nicanor Austriaco faults me for ignoring what he calls the “crucial biological fact” that “the nature of a particular cell is determined, not by the genetic state of the cell per se, but by its epigenetic state.”1 Once this “fact” comes into view, he insists, it becomes obvious that ANT is both technically and morally distinct from human cloning.
Father Austriaco acknowledges that I have got half the story right: I am correct in saying that both ANT and cloning involve the insertion of a somatic cell nucleus containing a reasonably complete genome into an enucleated oocyte. But, given what Father Austriaco calls “the primacy of epigenetics over genetics in determining cellular identity” (164), the mere transfer of the donor cell genome into the enucleated egg is not by itself sufficient to produce a new human organism. Something else must happen, too: the egg cell must reprogram the donor genome “into the epigenetic state associated with embryos.” “That,” continues Father Austriaco, “is the essential event that constitutes a new human organism” in the case of cloning. By contrast, ANT aims to prevent just this essential event from happening. The procedure deploys timely genetic manipulation to keep the egg from switching on the genes “associated with a single-cell human embryo.” By skillfully pre-programming the epigenetic determinants of the cellular identity of its product, then, ANT creates human cellular artifacts, but not cloned humans. Despite their apparent proximity, cloning and ANT are actually miles apart both technically and morally:
Given these biological facts, the difference between SCNT and ANT should be clear: with SCNT, the enucleated egg is allowed to reprogram the transferred genome so that an embryo is generated. In contrast, with ANT, the enucleated egg—because of genetic manipulations done either to the egg or to the donor cell or to both simultaneously—is prevented from reprogramming the transferred genome to an embryo-like epigenetic state. Thus, with ANT, the embryo-specific genes in the transferred genome are not turned on, and so no embryo—no organism—is generated. Instead, from the very beginning, a cellular artifact, with a subset of genes turned on that differs from the unique subset of genes turned on in a bona fide embryo, is created. Ideally, of course, this cellular artifact would be a source for pluripotent stem cells that, if necessary, could be licitly destroyed in the laboratory. In sum, contrary to Walker’s flawed proposal, ANT is technically, and therefore morally, distinguishable from cloning. (165)
. . . . . . . . . .
To read this article in its entirety, please download the free PDF or buy this issue.