Birth of mice produced by germ cell nuclear transfer

Abstract

That mammals can be cloned by nuclear transfer indicates that it is possible to reprogram the somatic cell genome to support full development. However, the developmental plasticity of germ cells is difficult to assess because genomic imprinting, which is essential for normal fetal development, is being reset at this stage. The anomalous influence of imprinting is corroborated by the poor development of mouse clones produced from primordial germ cells (PGCs) during imprinting erasure at embryonic day 11.5 or later. However, this can also be interpreted to mean that, unlike somatic cells, the genome of differentiated germ cells cannot be fully reprogrammed. We used younger PGCs (day 10.5) and eventually obtained four full-term fetuses. DNA methylation analyses showed that only embryos exhibiting normal imprinting developed to term. Thus, germ cell differentiation is not an insurmountable barrier to cloning, and imprinting status is more important than the origin of the nucleus donor cell per se as a determinant of developmental plasticity following nuclear transfer.

Mice Cloned by Nuclear Transfer from Somatic and ntES Cells Derived from the Same Individuals

“…The success rates for production of full-term pups per transferred embryo varied between 0% and 15.6%, with a mean rate of 3.0%, which is the similar to the success rates in previous reports [2][3][4][5][6][7][8][9][10][11]. We established 68 ntES cell lines from all seven individual mice, with a high success rate (16% to 82%, mean 39%).…”

“…We previously developed a microinjection-based nuclear transfer method to generate cloned mice from adult cumulus cells [2,3] and from tail-tip cells [4]. Ogura et al have reported success in cloning mice from Sertoli cells [5], natural killer T cells [6], and primordial germ cells [7]. However, as with other mammals, the overall efficiency of mouse cloning (the percentage of activated oocytes giving rise to live offspring) in all reports is less than 2%.…”

Recent advancements in cloning by somatic cell nuclear transfer

“…We also expect that NT using germ cells will provide important clues in understanding the factors that ensure the normal process of genomic reprogramming for producing totipotency. Our recent findings on the phenotypes of cloned embryos and offspring derived from PGCs at 10.5 dpc suggested a somatic cell nature of their genome; they showed stage-specific developmental arrest and hyperplastic placentas as those derived from SCNT [56]. Therefore, at some time during germ cell development between 10.5 dpc and the mature gamete stage, the germ cell genome acquires the ability to be reprogrammed fully for the beginning of new life.…”

Mice cloned from skin cells

“…In all species that have been cloned to date, cloning efficiencies remain disappointingly low: at best, a few percent of manipulated oocytes (4). In mice, NT has been successful with cells at various stages of differentiation, such as fetal germ cells (5), immature Sertoli cells (6), fibroblasts (7), T and B lymphocytes (8), natural killer T cells (9) and olfactory sensory neurons (10,11).…”