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Blastocysts produced by nuclear transfer between chicken blastodermal cells and rabbit oocytes

Interspecies nuclear transfer (INT) has been used as an invaluable tool for studying nucleus–cytoplasm interactions; and it may also be a method for rescuing endangered species whose oocytes are difficult to obtain. In the present study, we investigated interaction of the chicken genome with the rabbit oocyte cytoplasm. When chicken blastodermal cells were transferred into the perivitelline space of rabbit oocytes, 79.3% of the couplets were fused and 9.7% of the fused embryos developed to the blastocyst stage. Both M199 and SOF medium were used for culturing chicken–rabbit cloned embryos; embryo development was arrested at the 8‐cell stage obtained in SOF medium, while the rates of morulae and blastocysts were 12.1 and 9.7%, respectively, in M199 medium. Polymerase chain reaction (PCR) amplification of nuclear DNA and karyotype analyses confirmed that genetic material of morulae and blastocysts was derived from the chicken donor cells. Analysis mitochondrial constitution of the chicken–rabbit cloned embryos found that mitochondria, from both donor cells and enucleated oocytes, co‐existed. Our results suggest that: (1) chicken genome can coordinate with rabbit oocyte cytoplasm in early embryo development; (2) there may be an 8‐ to 16‐cell stage block for the chicken–rabbit cloned embryos when cultured in vitro; (3) mitochondrial DNA from the chicken donor cells was not eliminated until the blastocyst stage in the chicken–rabbit cloned embryos; (4) factors existing in ooplasm for somatic nucleus reprogramming may be highly conservative. Mol. Reprod. Dev. 69: 296–302, 2004. © 2004 Wiley‐Liss, Inc.