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

Hypoxic stress induces, but cannot sustain trophoblast stem cell differentiation to labyrinthine placenta due to mitochondrial insufficiency

Dysfunctional stem cell differentiation into placental lineages is associated with gestational diseases. Of the differentiated lineages available to trophoblast stem cells (TSC), elevated O2 and mitochondrial function are necessary to placental lineages at the maternal–placental surface and important in the etiology of preeclampsia. TSC lineage imbalance leads to embryonic failure during uterine implantation. Stress at implantation exacerbates stem cell depletion by decreasing proliferation and increasing differentiation. In an implantation site O2 is normally ~ 2%. In culture, exposure to 2% O2 and fibroblast growth factor 4 (FGF4) enabled the highest mouse TSC multipotency and proliferation. In contrast, hypoxic stress (0.5% O2) initiated the most TSC differentiation after 24 h despite exposure to FGF4. However, hypoxic stress supported differentiation poorly after 4–7 days, despite FGF4 removal. At all tested O2 levels, FGF4 maintained Warburg metabolism; mitochondrial inactivity and aerobic glycolysis. However, hypoxic stress suppressed mitochondrial membrane potential and maintained low mitochondrial cytochrome c oxidase (oxidative phosphorylation/OxPhos), and high pyruvate kinase M2 (glycolysis) despite FGF4 removal. Inhibiting OxPhos inhibited optimum differentiation at 20% O2. Moreover, adding differentiation-inducing hyperosmolar stress failed to induce differentiation during hypoxia. Thus, differentiation depended on OxPhos at 20% O2; hypoxic and hyperosmolar stresses did not induce differentiation at 0.5% O2. Hypoxia-limited differentiation and mitochondrial inhibition and activation suggest that differentiation into two lineages of the labyrinthine placenta requires O2 \u3e 0.5–2% and mitochondrial function. Stress-activated protein kinase increases an early lineage and suppresses later lineages in proportion to the deviation from optimal O2 for multipotency, thus it is the first enzyme reported to prioritize differentiation

Serine-threonine kinases and transcription factors active in signal transduction are detected at high levels of phosphorylation during mitosis in preimplantation embryos and trophoblast stem cells

Serine-threonine kinases and transcription factors play important roles in the G1-S phase progression of the cell cycle. Assays that use quantitative fluorescence by immunocytochemical means, or that measure band strength during Western blot analysis, may have confused interpretations if the intention is to measure G1-S phase commitment of a small subpopulation of phosphorylated proteins, when a larger conversion of the same population of proteins can occur during late G2 and M phases. In mouse trophoblast stem cells (TSC), a human placental cell line (HTR), and/or mouse preimplantation embryos, 8/19 ser- ine-threonine and tyrosine kinases, 3/8 transcription factors, and 8/14 phospho substrate and miscellaneous proteins were phosphorylated at higher levels in M phase than in interphase. Most phosphoproteins appeared to associate with the spindle complex during M phase, but one (p38MAPK) associated with the spindle pole and five (Cdx2, MEK1, 2, p27, and RSK1) associated with the DNA. Phosphorylation was detected throughout apparent metaphase, anaphase and telophase for some proteins, or for only one of these segments for others. The phosphorylation was from 2.1- to 6.2-fold higher during M phase compared with interphase. These data suggest that, when planning and interpreting quantitative data and perturbation experiments, consideration must be given to the role of serine-threonine kinases and transcription factors during decision making in M phase as well as in G1-S phase

Paternal effects on early embryogenesis

Historically, less attention has been paid to paternal effects on early embryogenesis than maternal effects. However, it is now apparent that certain male factor infertility phenotypes are associated with increased DNA fragmentation and/or chromosome aneuploidies that may compromise early embryonic development. In addition, there is a growing body of evidence that the fertilizing sperm has more function than just carrying an intact, haploid genome. The paternally inherited centrosome is essential for normal fertilization, and the success of higher order chromatin packaging may impact embryogenesis. Epigenetic modifications of sperm chromatin may contribute to the reprogramming of the genome, and sperm delivered mRNA has also been hythesized to be necessary for embryogenesis. There is less information about the epigenetic factors affecting embryogenesis than genetic factors, but the epigenetics of gamete and early embryogenesis is a rapidly advancing field