This reprint considers a wide variety of topics concerning molecular and clinical advances in understanding early mammalian embryo development. The authors of various chapters of this book examine ...oocyte biology, preimplantation embryo development, blastocyst implantation in the uterus, and second cellular lineage differentiation. In addition, epigenetic contributions to reproduction, which may occur throughout pregnancy and in resultant offspring, are also considered. Environmentally induced epigenetic changes in germ cells can render mammalian offspring less healthy, and these changes can be difficult to reverse. Included in these changes are those caused by assisted reproductive technologies (ARTs). It remains to be determined whether the healthiest preimplantation embryos develop in vitro in conditions that mimic the physiological environment in vivo or whether simpler conditions can also foster this development in vitro. In this regard, a number of advances as well as challenges in ART are considered by the authors of the chapters included in this book.
MSG alters metabolism, especially in the brain, when administered to experimental animals via gavage or similar means. Such administration is, however, not applicable to humans. More recently, ...though, MSG was shown to have these effects even when added to the food of mammals. Moreover, the levels of MSG in food needed to cause these metabolic changes are the same as those needed for optimum flavor enhancement. Near physiological concentrations of glutamate also cause mammalian blastocysts to develop with fewer cells, especially in their inner cell masses, when these embryos are cultured with this amino acid. We propose that consumption of MSG in food may overwhelm the otherwise well-regulated glutamate signaling needed for optimal development by pre- and peri-implantation mammalian embryos. In addition to immediate changes in cellular proliferation and differentiation as embryos develop, MSG ingestion during early pregnancy might result in undesirable conditions, including metabolic syndrome, in adults. Since these conditions are often the result of epigenetic changes, they could become transgenerational. In light of these possibilities, we suggest several studies to test the merit of our hypothesis.
Human (h) and mouse (m) embryonic stem (ES) cells need specific amino acids to proliferate. mES cells require threonine (Thr) metabolism for epigenetic histone modifications. Thr is converted to ...glycine and acetyl CoA, and the glycine is metabolized specifically to regulate trimethylation of lysine (Lys) residue 4 in histone H3 (H3K4me3). DNA methylation and methylation of other H3 Lys residues remain unimpaired by Thr deprivation in mES cell culture medium. Similarly, hES cells require methionine (Met) to maintain the Met-SAM (S-adenosyl methionine) cycle of 1-carbon metabolism also for H3K4me3 formation. H3K4me3 is needed specifically to regulate and maintain both mES and hES cell proliferation and their pluripotent states. Better understanding of this regulation is essential since treatment of human diseases and disorders will increasingly involve hES cells. Furthermore, since ES cells are derived from their progenitor cells in preimplantation blastocysts, they serve as models of 1-carbon metabolism in these precursors of all mammalian tissues and organs. One-carbon metabolism challenges, such as a maternal low protein diet (LPD) during preimplantation blastocyst development, contribute to development of metabolic syndrome and related abnormalities in adults. These 1-carbon metabolism challenges result in altered epigenetic DNA and histone modifications in ES progenitor cells and the tissues and organs to which they develop. Moreover, the modified histones could have extracellular as well as intracellular effects, since histones are secreted in uterine fluid and influence early embryo development. Hence, the mechanisms and transgenerational implications of these altered epigenetic DNA and histone modifications warrant concerted further study.
The articles in this Special Issue address a wide variety of topics concerning molecular and clinical advances in understanding early embryo development ....
The osmolality of mouse oviductal fluid ranges from about 300 mOsmol/kg in the ampulla 0-3 h post coitus (h p.c.) to more than 350 mOsmol/kg in the isthmus 34-36 h p.c. Thus, it has been surprising ...to find that development of one-cell and cleavage-stage mouse embryos arrests
in media exceeding 300 mOsmol/kg, and they develop best in unphysiological, hypotonic media. The glycine concentration in oviductal fluid can, however, rescue development in hypertonic media, so physiological conditions
and
likely work together to foster embryo well-being. Glycine acts on one-cell and cleavage-stage mouse embryos through the glycine-gated chloride channel, GLRA4, and uptake
the glycine neurotransmitter transporter, GLYT1. Since these processes lead to further signaling in neurons, the presence and function of such signaling in preimplantation embryos also should be investigated. The more we know about the interactions of physiological processes and conditions
, the better we would be able to reproduce them
. Such improvements in assisted reproductive technology (ART) could improve patient outcomes for IVF and potentially help prevent unwanted developmental abnormalities in early embryos, which might include undesirable epigenetic DNA and histone modifications. These epigenetic modifications may lead to transgenerational adult disorders such as metabolic syndrome and related conditions.
Embryo/fetal nutrition and the environment in the reproductive tract influence the subsequent risk of developing adult diseases and disorders, as formulated in the Barker hypothesis. Metabolic ...syndrome, obesity, heart disease, and hypertension in adulthood have all been linked to unwanted epigenetic programing in embryos and fetuses. Multiple studies support the conclusion that environmental challenges, such as a maternal low-protein diet, can change one-carbon amino acid metabolism and, thus, alter histone and DNA epigenetic modifications. Since histones influence gene expression and the program of embryo development, these epigenetic changes likely contribute to the risk of adult disease onset not just in the directly affected offspring, but for multiple generations to come. In this paper, we hypothesize that the effects of parental nutritional status on fetal epigenetic programming are transgenerational and warrant further investigation. Numerous studies supporting this hypothesis are reviewed, and potential research techniques to study these transgenerational epigenetic effects are offered.
We sought to determine whether the Reflective Practice Questionnaire (RPQ) is a reliable measure of reflective capacity and related characteristics in medical students. We also planned to learn how ...the RPQ could be used in medical education.
The RPQ is a 40 item self-report questionnaire that includes a multi-faceted approach to measuring reflective capacity. It also includes sub-scales on several other theoretically relevant constructs such as desire for improvement, confidence, stress, and job satisfaction. The reliabilities of reflective capacity and other sub-scales were determined by calculating their Cronbach alpha reliability values. In the present study, the RPQ was answered by 98 graduating fourth-year medical students from an American University, and these RPQ scores were compared with general public and mental health practitioner samples from a prior study using ANOVA and Bonferroni adjusted comparisons.
Medical students reported a higher reflective capacity than the general public sample, but students were statistically indistinguishable from the mental health practitioner sample. For medical students, reflective capacity was associated with features of confidence, stress, and desire for improvement. Job satisfaction was positively associated with confidence in communication with patients, and negatively associated with stress when interacting with patients. A cluster analysis revealed that around 19% of the medical students exhibited a relatively high level of anxiety interacting with patients, 23% were less engaged, 5% were dissatisfied, and 7% expressed a level of over-confidence in their knowledge and skills that was concerning.
The RPQ is a reliable measure of reflective capacity (Chronbach's alpha value = 0.84) and related characteristics (Cronbach's alpha values from 0.75 to 0.83) in medical students. The RPQ can be used as part of pre-post evaluations of medical education initiatives, to complement student self-reflection activities in the curriculum, and to identify students who might benefit from targeted intervention.
A relatively large branched-chain amino acid (BCAA) supplement, consumed for more than 10 days, appears to be especially effective at alleviating muscle damage and soreness during intense human ...training. However, perturbations in amino acid and protein consumption could have unwanted transgenerational effects on male and female reproduction. This paper hypothesizes that isoleucine consumption by female mice from days 2 to 10 of pregnancy will alter fetal and placental growth later in gestation. Mice that had received 118 mM isoleucine in their drinking water delivered pups on day 19 of pregnancy that were 9% larger than normal, whereas the reverse was true for pups born on day 20. Moreover, the inverse correlation between birth weight and litter size was lost in mice that previously consumed excess isoleucine. Similarly, the normal correlations between fetal and placental weights were lost by day 18 of pregnancy in mice that had consumed excess isoleucine. Mice that consumed excess isoleucine had placentas smaller than, and fetuses larger than normal on day 18 of pregnancy, but the reverse was true on day 15. Other unintended and unexpected effects of BCAA consumption should be studied more thoroughly due to the increasing use of BCAAs to alleviate muscle damage and soreness in athletes.
The conversion of lysine to glutamate is needed for signaling in all plants and animals. In mouse embryonic stem (mES) cells, and probably their progenitors, endogenous glutamate production and ...signaling help maintain cellular pluripotency and proliferation, although the source of glutamate is yet to be determined. If the source of glutamate is lysine, then lysine deprivation caused by maternal low-protein diets could alter early embryo development and, consequently, the health of the offspring in adulthood. For these reasons, we measured three pertinent variables in human embryonic stem (hES) cells as a model for the inner cell masses of human blastocysts. We found that RNA encoding the alpha-aminoadipic semialdehyde synthase enzyme, which regulates glutamate production from lysine, was highly expressed in hES cells. Moreover, the mean amount of lysine consumed by hES cells was 50% greater than the mean amount of glutamate they produced, indicating that lysine is likely converted to glutamate in these cells. Finally, hES cells expressed RNA encoding at least two glutamate receptors. Since this may also be the case for hES progenitor cells in blastocysts, further studies are warranted to verify the presence of this signaling process in hES cells and to determine whether lysine deprivation alters early mammalian embryo development.
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