Microinjection of cytoplasm or mitochondria derived from somatic cells affects parthenogenetic development of murine oocytes

Cloned mammals are readily obtained by nuclear transfer using cultured somatic cells; however, the rate of generating live offspring from the reconstructed embryos remains low. In nuclear transfer procedures, varying quantities of donor cell mitochondria are transferred with nuclei into recipient oocytes, and mitochondrial heteroplasmy has been observed. A mouse model was used to examine whether transferred mitochondria affect the development of the reconstructed oocytes. Cytoplasm or purified mitochondria from somatic cells derived from the external ear, skeletal muscle, and testis of Mus spretus mice or cumulus cells of Mus musculus domesticus mice were transferred into M. m. domesticus (B6SJLF1 and B6D2F1) oocytes to observe parthenogenetic development through the morula stage. All B6D2F1 oocytes injected with somatic cytoplasm or mitochondria showed delayed development when compared to oocytes injected with buffer. The developmental rates were not different among injected cell sources, with the exception of testis-derived donor cells injected into B6SJLF1 oocytes (P < 0.01). The developmental rate of B6D2F1 oocytes injected with buffer alone (98.8% survival) was different from those injected with somatic cytoplasm (60.8% survival) or somatic mitochondria (56.5% survival) (P < 0.01). Conversely, injection of ooplasm into B6D2F1 oocytes did not affect parthenogenetic development (1100% survival). Our results indicate that injection of somatic cytoplasm or mitochondria affected parthenogenetic development of murine oocytes. These results have further implications for in vitro fertilization protocols employing ooplasmic transfer where primary oocyte failure is not confirmed.