Early transcription from the maternal genome controlling blastomere integrity in mouse two-cell-stage embryos

A speculative outlook on embryonic aneuploidy: Can molecular pathways be involved?

The journey of embryonic development starts at oocyte fertilization, which triggers a complex cascade of events and cellular pathways that guide early embryogenesis. Recent technological advances have greatly expanded our knowledge of cleavage-stage embryo development, which is characterized by an increased rate of whole-chromosome losses and gains, mixoploidy, and atypical cleavage morphokinetics. Embryonic aneuploidy significantly contributes to implantation failure, spontaneous miscarriage, stillbirth or congenital birth defects in both natural and assisted human reproduction. Essentially, early embryo development is strongly determined by maternal factors. Owing to considerable limitations associated with human oocyte and embryo research, the use of animal models is inevitable. However, cellular and molecular mechanisms driving the error-prone early stages of development are still poorly described. In this review, we describe known events that lead to aneuploidy in mammalian oocytes and preimplantation embryos. As the processes of oocyte and embryo development are rigorously regulated by multiple signal-transduction pathways, we explore the putative role of signaling pathways in genomic integrity maintenance. Based on the existing evidence from human and animal data, we investigate whether critical early developmental pathways, like Wnt, Hippo and MAPK, together with distinct DNA damage response and DNA repair pathways can be associated with embryo genomic instability, a question that has, so far, remained largely unexplored.

Gasotransmitters in Gametogenesis and Early Development: Holy Trinity for Assisted Reproductive Technology-A Review

Creation of both gametes, sperm and oocyte, and their fusion during fertilization are essential step for beginning of life. Although molecular mechanisms regulating gametogenesis, fertilization, and early embryonic development are still subjected to intensive study, a lot of phenomena remain unclear. Based on our best knowledge and own results, we consider gasotransmitters to be essential for various signalisation in oocytes and embryos. In accordance with nitric oxide (NO) and hydrogen sulfide (H₂S) physiological necessity, their involvement during oocyte maturation and regulative role in fertilization followed by embryonic development have been described. During these processes, NO- and H₂S-derived posttranslational modifications represent the main mode of their regulative effect. While NO represent the most understood gasotransmitter and H₂S is still intensively studied gasotransmitter, appreciation of carbon monoxide (CO) role in reproduction is still missing. Overall understanding of gasotransmitters including their interaction is promising for reproductive medicine and assisted reproductive technologies (ART), because these approaches contend with failure of in vitro assisted reproduction.

Different chromatin and energy/redox responses of mouse morulae and blastocysts to slow freezing and vitrification

BACKGROUND

The ability to cryopreserve mammalian embryos has become an integral part of assisted reproduction, both in human and veterinary medicine. Despite differences in the size and physiological characteristics of embryos from various species, the embryos have been frozen by either of two procedures: slow freezing or vitrification. The aim of our study was to compare the effect of slow freezing and vitrification to the chromatin structure, energy status and reactive oxygen species production of mouse morulae and blastocysts.

METHODS

Mouse morulae and blastocysts were randomly allocated into vitrification, slow freezing and control groups. For slow freezing, Dulbecco phosphate buffered saline based 10% glicerol solution was used. For vitrification, G-MOPS™ based solution supplemented with 16% ethylene glycol, 16% propylene glycol, Ficoll (10 mg/ml) and sucrose (0.65 mol/l) was used. After warming, the chromatin integrity, mitochondrial distribution pattern and energy/oxidative status were compared among groups.

RESULTS

Cryopreservation affected chromatin integrity at a greater extent at the morula than the blastocyst stage. Chromatin damage induced by slow freezing was more relevant compared to vitrification. Slow freezing and vitrification similarly affected mitochondrial distribution pattern. Greater damage was observed at the morula stage and it was associated with embryo grade. Cryopreservation altered the quantitative bioenergy/redox parameters at a greater extent in the morulae than in the blastocysts. Effects induced by slow freezing were not related to embryo grade or mitochondrial pattern, as affected embryos were of all grades and with both mitochondrial patterns. However, effects induced by vitrification were related to mitochondrial pattern, as only embryos with homogeneous mitochondrial pattern in small aggregates had reduced energy status.

CONCLUSIONS

This study shows for the first time the joint assessment of chromatin damage and mitochondrial energy/redox potential in fresh and frozen mouse embryos at the morula and blastocyst stage, allowing the comparison of the effects of the two most commonly used cryopreservation procedures.

Vitrification preserves chromatin integrity, bioenergy potential and oxidative parameters in mouse embryos

BACKGROUND

The aim of this study was to evaluate the effects of vitrification on morpho-functional parameters (blastomere/chromatin integrity and bioenergy/oxidative potential) of mouse preimplantation embryos.

METHODS

In vivo produced mouse (4/16-cell, morulae and blastocyst-stage) embryos were randomly divided into vitrification and control groups. For vitrification, embryos were exposed to a 2-step loading of ethylene glycol and propylene glycol, before being placed in a small nylon loop and submerged into liquid nitrogen. After warming, the cryoprotectants were diluted by a 3-step procedure. Embryo morphology, chromatin integrity and energy/oxidative status were compared between groups.

RESULTS

Vitrification induced low grade blastomere cytofragmentation (P < 0.05) and low chromatin damage only in embryos at the morula stage (P < 0.001). Mitochondrial (mt) distribution pattern was affected by vitrification only in early embryos (P < 0.001). Mitochondrial activity did not change upon vitrification in morula-stage embryos but it was reduced in blastocyst-stage embryos (P < 0.05). Intracellular ROS levels significantly increased in embryos at the morula and blastocyst stages (P < 0.001). Colocalization of active mitochondria and ROS increased only in vitrified blastocysts.

CONCLUSIONS

In conclusion, this study elucidates the developmentally-related and mild effects of vitrification on morphology, nuclear and bioenergy/oxidative parameters of mouse embryos and demonstrates that vitrification is a suitable method for preserving predictive parameters of embryo ability to induce a full-term pregnancy.

The roles of parathyroid hormone-like hormone during mouse preimplantation embryonic development

Parathyroid hormone-like hormone (PTHLH) was first identified as a parathyroid hormone (PTH)-like factor responsible for humoral hypercalcemia in malignancies in the 1980s. Previous studies demonstrated that PTHLH is expressed in multiple tissues and is an important regulator of cellular and organ growth, development, migration, differentiation, and survival. However, there is a lack of data on the expression and function of PTHLH during preimplantation embryonic development. In this study, we investigated the expression characteristics and functions of PTHLH during mouse preimplantation embryonic development. The results show that Pthlh is expressed in mouse oocytes and preimplantation embryos at all developmental stages, with the highest expression at the MII stage of the oocytes and the lowest expression at the blastocyst stage of the preimplantation embryos. The siRNA-mediated depletion of Pthlh at the MII stage oocytes or the 1-cell stage embryos significantly decreased the blastocyst formation rate, while this effect could be corrected by culturing the Pthlh depleted embryos in the medium containing PTHLH protein. Moreover, expression of the pluripotency-related genes Nanog and Pou5f1 was significantly reduced in Pthlh-depleted embryos at the morula stage. Additionally, histone acetylation patterns were altered by Pthlh depletion. These results suggest that PTHLH plays important roles during mouse preimplantation embryonic development.