Appendix N. 
413 
Table 1 
Donor nucleus 
Mice 
(% of blastocysts) 
Phenotype 
Ref. 
Fertilized zygote 
30 - 50 % 
Normal 
Nuclear 
transfer 
from 
ESceU 
15 - 30 % 
Most if not 
all clones 
are 
abnormal 
1 
Cumulus cell, 
fibroblast 
1 - 3 % 
2 
B, T ceU 
< 1/3000 
3 , 
Development of normal embryos and embryos cloned from ES cell 
and somatic donor nuclei. Note that normal and ES cell derived 
blastocysts have a similar potency to develop to term if calculated 
from the fraction of transplanted blastocysts. 
1: (Eggan et al., 2001; Eggan et al., 2002; Rideout et al., 2000); 2 
(Wakayama et al., 1998; Wakayama and Yanagimachi, 1999); 3 
(Hochedlinger and Jaenisch, 2002a). 
Acknowledgements 
I thank my colleagues Bob Weinberg, Gerry Fink, George Daley and 
Andy Chess for critical and constructive comments on this 
manuscript. 
ENDNOTES 
1 Reprocrramniinq : Th© genome of a somatic cell is in an epigenetic state that is 
appropriate for the respective tissue and assures the expression of the tissue specific 
genes (in mammary gland cells, for example, those genes impxjrtant for mammary 
gland function such as milk production). In cloning, the somatic nucleus must activate 
those genes that are needed for embryonic development but which are silent in the 
donor cell in order for the cloned embryo to survive. The egg cytoplasm contains 
“reprogramming factors" that can convert the epigenetic state (see endnote 3) 
characteristic of the somatic donor nucleus to one that is appropnate for an embryomc 
cell. This process is very inefficient leading to inappropnate expression of many genes 
and causes most clones to fail early. 
PRE -PUBLICATION VERSION 
