Effects of SAPK/JNK inhibitors on preimplantation mouse embryo development are influenced greatly by the amount of stress induced by the media.

Stress-activated protein kinase/c-Jun kinase (SAPK/JNK) is thought to be necessary for preimplantation embryonic development (Maekawa et al., 2005). However, media increases SAPK/JNK phosphorylation and these levels negatively correlate with embryonic development (Wang et al., 2005). Culture-induced stress could confuse analysis of the role of SAPK in development. In this study, we tested how SAPK/JNK inhibitors influence embryonic development in optimal and non-optimal media and define the contribution of cell survival and proliferation to the embryonic response to these media. SAPK/JNK inhibitors retard embryonic development in suboptimal Ham's F10, but improve development in optimal potassium (K+) simplex optimized media (KSOM) +AA. In KSOM + amino acids (KSOM+AA), two SAPK/JNK inhibitors increase the rate of cavitation and hatching. These data suggest that (i) SAPK/JNK mediates the response to culture stress, not normal preimplantation embryonic development and (ii) SAPK/JNK inhibitors may be useful in ameliorating embryo stress caused by culture. To define the effects of media, we assayed the contribution of cell survival and proliferation and the differences in total cell number of cultured embryos. Embryos cultured from E3.5+24 h in the suboptimal medium (Ham's F10) induced significant but small increases in TdT (terminal deoxynucleotidyl transferase)-mediated dUDP nick-end labelling (TUNEL) positive cells. Bromodeoxyuridine (BrdU) incorporation in suboptimal Ham's F10 was significantly lower than in optimal KSOM+AA, suggesting that cell cycle arrest also contributes to slower increase in cell number in stressful media. This is the first report where TUNEL and BrdU were both assayed to define the relative contribution of cell cycle/S phase commitment and apoptosis to lessened cell number increase during embryo culture.