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"Embryonic Development - physiology"
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Proteomics Analysis Reveals that Warburg Effect along with Modification in Lipid Metabolism Improves In Vitro Embryo Development under Low Oxygen
The molecular mechanism regulating embryo development under reduced oxygen tension remains elusive. This study aimed to identify the molecular mechanism impacting embryo development under low oxygen conditions. Buffalo embryos were cultured under 5% or 20% oxygen and were evaluated according to their morphological parameters related to embryo development. The protein profiles of these embryos were compared using iTRAQ-based quantitative proteomics. Physiological O2 (5%) significantly promoted blastocyst yield, hatching rate, embryo quality and cell count as compared to atmospheric O2 (20%). The embryos in the 5% O2 group had an improved hatching rate of cryopreserved blastocysts post-warming (p < 0.05). Comparative proteome profiles of hatched blastocysts cultured under 5% vs. 20% O2 levels identified 43 differentially expressed proteins (DEPs). Functional analysis indicated that DEPs were mainly associated with glycolysis, fatty acid degradation, inositol phosphate metabolism and terpenoid backbone synthesis. Our results suggest that embryos under physiological oxygen had greater developmental potential due to the pronounced Warburg Effect (aerobic glycolysis). Moreover, our proteomic data suggested that higher lipid degradation, an elevated cholesterol level and a higher unsaturated to saturated fatty acid ratio might be involved in the better cryo-survival ability reported in embryos cultured under low oxygen. These data provide new information on the early embryo protein repertoire and general molecular mechanisms of embryo development under varying oxygen levels.
Journal Article
Impact of Group vs Individual Embryo Culture Strategies on Blastocyst and Clinical Outcomes
Embryo culture is one of the most important steps in an assisted reproduction laboratory. Embryos can be cultured individually, one embryo per media drop, or in groups, culturing several embryos in the same media drop. Due to the controversy generated on this subject, we wondered which embryo culture method would have the best results in terms of quality and blastocyst formation rate. We designed a prospective randomized study comparing two different embryo culture strategies: group and individual embryo culture. The data were obtained from 830 embryos from 103 egg donation treatments. The zygotes were randomized into two groups: individual culture (group 1) or group culture (group 2). The embryos were cultured in 35-µl drops until day 5 when they were classified morphologically. We observed a significant increase in the blastocyst formation rate and in the usable embryo rate in individual culture on day 5 compared to group culture. However, good embryo quality (A/B blastocysts), implantation, and pregnancy rates were similar regardless of the type of embryo-culture. As a conclusion, individual culture may increase blastocyst formation rate and may benefit embryo quality on day 5. Our results support previous reports suggesting that individual culture could improve embryo development.
Journal Article
TILT: Time-Lapse Imaging Trial—a pragmatic, multi-centre, three-arm randomised controlled trial to assess the clinical effectiveness and safety of time-lapse imaging in in vitro fertilisation treatment
Background
Subfertility is a common problem for which in vitro fertilisation (IVF) treatment is commonly recommended. Success rates following IVF are suboptimal and have remained static over the last few years. This imposes a considerable financial burden on overstretched healthcare resources. Time-lapse imaging (TLI) of developing embryos in IVF treatment is hypothesised to improve the success rates of treatment. This may be either by providing undisturbed culture conditions or by improving the predictive accuracy for optimal embryo selection from a cohort of available embryos. However, the current best evidence for its effectiveness is inconclusive.
Methods
The time-lapse imaging trial is a pragmatic, multi-centre, three-arm parallel-group randomised controlled trial using re-randomisation. The primary objective of the trial is to determine if the use of TLI or undisturbed culture in IVF treatment results in a higher live birth rate when compared to current standard methods of embryo incubation and assessment. Secondary outcomes include measures of clinical efficacy and safety. The trial will randomise 1575 participants to detect an increase in live birth from 26.5 to 35.25%.
Discussion
In the absence of high-quality evidence, there is no current national guidance, recommendation or policy for the use of TLI. The use of TLI is not consistently incorporated into standard IVF care. A large, pragmatic, multi-centre, trial will provide much needed definitive evidence regarding the effectiveness of TLI. If proven to be effective, its incorporation into standard care would translate into significant clinical and economic benefits. If not, it would allow allocation of resources to more effective interventions.
Trial registration
ISRCTN registry
ISRCTN17792989
. Prospectively registered on 18 April 2018
Journal Article
Fgf8 dynamics and critical slowing down may account for the temperature independence of somitogenesis
Somitogenesis, the segmentation of the antero-posterior axis in vertebrates, is thought to result from the interactions between a genetic oscillator and a posterior-moving determination wavefront. The segment (somite) size is set by the product of the oscillator period and the velocity of the determination wavefront. Surprisingly, while the segmentation period can vary by a factor three between 20 °C and 32 °C, the somite size is constant. How this temperature independence is achieved is a mystery that we address in this study. Using RT-qPCR we show that the endogenous
fgf8
mRNA concentration decreases during somitogenesis and correlates with the exponent of the shrinking pre-somitic mesoderm (PSM) size. As the temperature decreases, the dynamics of
fgf8
and many other gene transcripts, as well as the segmentation frequency and the PSM shortening and tail growth rates slows down as T–T
c
(with T
c
= 14.4 °C). This behavior characteristic of a system near a critical point may account for the temperature independence of somitogenesis in zebrafish.
In Zebrafish, the dynamics of fgf8 and other gene transcripts as well as segmentation frequency, shortening of pre-somitic mesoderm and tail growth rate slows down with lower temperature. This may explain the temperature independence of somitogenesis.
Journal Article
Vitrification of immature bovine cumulus-oocyte complexes: effects of cryoprotectants, the vitrification procedure and warming time on cleavage and embryo development
Background
The present studies evaluated the effects of cryoprotectants, the vitrification procedure and time in the warming solution containing sucrose on cleavage and embryo development of immature (GV stage) bovine cumulus-oocyte complexes (COCs).
Methods
Two experiments were conducted. In Experiment 1, COCs (n = 420) were randomly assigned to four groups: 1) Control group: no treatment; 2) VS1 group: COCs were exposed to vitrification solution 1 (VS1) containing 7.5% ethylene glycol [EG] + 7.5% dimethyl sulfoxide [DMSO] + 20% calf serum [CS] in TCM-199 at 37 C for 5 min; 3) VS1 + VS2 group: COCs were exposed to VS1 for 5 min followed by VS2 (15% EG + 15% DMSO + 17.1% sucrose + 20% CS) at 37 C for 45–60 sec; and 4) Vitrified group: COCs were exposed to VS1 and VS2, loaded on cryotops, vitrified in liquid nitrogen and then warmed in TCM-199 + 17.1% sucrose + 20% CS at 37 C for 1 min. In Experiment 2, COCs (n = 581) were assigned to the same groups, but those in VS1, VS1 + VS2 and Vitrified groups were sub-divided and exposed to the warming solution for either 1 or 5 min. After treatment and/or warming, all COCs in both experiments underwent
in vitro
maturation,
in vitro
fertilization and
in vitro
culture.
Results
Cleavage and blastocyst rates did not differ among Control, VS1 and VS1 + VS2 groups in either experiment. In Experiment 2, there was no effect of time in the warming solution.
However, both cleavage and blastocyst rates were lower (
P
< 0.001) in the Vitrified group than in the Control, VS1 and VS1 + VS2 groups (40.9 and 1.6% vs 92.2 and 34.4%, 79.4 and 25.2%, and 80.2 and 20.8%, respectively in Experiment 1, and 25.0 and 1.7% vs 75.3 and 27.2%, 67.9 and 19.5%, and 62.7 and 22.5%, respectively in Experiment 2).
Conclusions
The permeating cryoprotectants (EG and DMSO) present in VS1 and VS2 solutions and the time in the warming solution containing sucrose had no adverse effects on cleavage and blastocyst rates of immature bovine COCs. However, cleavage rate and early embryo development were reduced following the vitrification and warming.
Journal Article
Better Quality and More Usable Embryos Obtained on Day 3 Cultured in 5% Than 20% Oxygen
To evaluate the effect of atmospheric oxygen (O2) concentration on embryonic development, a controlled and randomized study using the sibling oocytes was carried out. A total of 147 patients were studied. Embryos were cultured in O2 concentration 20% versus 5% during the gamete, zygote, and first 3 days. The mean cell numbers of embryo (7.69 ± 1.91 vs 7.20 ± 1.82, P = .011) and rate of clinically useable embryos (81.62% vs 77.22%, P = .017) were significantly higher in 5% O2 than in 20% O2. There was no difference in the zygote developmental stage, day 2, day 4, and blastocyst stage. The quality of blastocyst (both inner cell mass and trophectoderm) showed no difference. Also, there was no increase in embryos fragmentation and uneven cells in 20% O2 culture condition. In conclusion, 20% O2 reduced the mean cell numbers of embryo and the number of clinically useable embryos on day 3. However, there was no subsequent negative impact on development of day 4 and blastocyst stage.
Journal Article
Roles and regulation of histone methylation in animal development
Histone methylation can occur at various sites in histone proteins, primarily on lysine and arginine residues, and it can be governed by multiple positive and negative regulators, even at a single site, to either activate or repress transcription. It is now apparent that histone methylation is critical for almost all stages of development, and its proper regulation is essential for ensuring the coordinated expression of gene networks that govern pluripotency, body patterning and differentiation along appropriate lineages and organogenesis. Notably, developmental histone methylation is highly dynamic. Early embryonic systems display unique histone methylation patterns, prominently including the presence of bivalent (both gene-activating and gene-repressive) marks at lineage-specific genes that resolve to monovalent marks during differentiation, which ensures that appropriate genes are expressed in each tissue type. Studies of the effects of methylation on embryonic stem cell pluripotency and differentiation have helped to elucidate the developmental roles of histone methylation. It has been revealed that methylation and demethylation of both activating and repressive marks are essential for establishing embryonic and extra-embryonic lineages, for ensuring gene dosage compensation via genomic imprinting and for establishing body patterning via HOX gene regulation. Not surprisingly, aberrant methylation during embryogenesis can lead to defects in body patterning and in the development of specific organs. Human genetic disorders arising from mutations in histone methylation regulators have revealed their important roles in the developing skeletal and nervous systems, and they highlight the overlapping and unique roles of different patterns of methylation in ensuring proper development.
Journal Article
Origin and function of the yolk sac in primate embryogenesis
Human embryogenesis is hallmarked by two phases of yolk sac development. The primate hypoblast gives rise to a transient primary yolk sac, which is rapidly superseded by a secondary yolk sac during gastrulation. Moreover, primate embryos form extraembryonic mesoderm prior to gastrulation, in contrast to mouse. The function of the primary yolk sac and the origin of extraembryonic mesoderm remain unclear. Here, we hypothesise that the hypoblast-derived primary yolk sac serves as a source for early extraembryonic mesoderm, which is supplemented with mesoderm from the gastrulating embryo. We discuss the intricate relationship between the yolk sac and the primate embryo and highlight the pivotal role of the yolk sac as a multifunctional hub for haematopoiesis, germ cell development and nutritional supply.
Why do human embryos need a yolk sac and how does it form? This Perspective by Thorsten Boroviak and Connor Ross explores the development and function of the yolk sac in primate embryogenesis.
Journal Article
Evidence for Developmental Programming of Cerebral Laterality in Humans
Adverse fetal environments are associated with depression, reduced cognitive ability and increased stress responsiveness in later life, but underlying mechanisms are unknown. Environmental pressures on the fetus, resulting from variations in placental function and maternal nutrition, health and stress might alter neurodevelopment, promoting the development of some brain regions over others. As asymmetry of cerebral activity, with greater right hemisphere activity, has been associated with psychopathology, we hypothesized that regional specialization during fetal life might be reflected persistently in the relative activity of the cerebral hemispheres. We tested this hypothesis in 140 healthy 8-9 year-old children, using tympanic membrane temperature to assess relative blood flow to the cerebral hemispheres at rest and following psychosocial stress (Trier Social Stress Test for Children). Their birth weight and placental weight had already been measured when their mothers took part in a previous study of pregnancy outcomes. We found that children who had a smaller weight at birth had evidence of greater blood flow to the right hemisphere than to the left hemisphere (r = -.09, P = .29 at rest; r = -.18, P = .04 following stress). This finding was strengthened if the children had a relatively low birth weight for their placental weight (r = -.17, P = .05 at rest; r = -.31, P = .0005 following stress). Our findings suggest that lateralization of cerebral activity is influenced persistently by early developmental experiences, with possible consequences for long-term neurocognitive function.
Journal Article