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Updated: May 1, 2026
Loss- and Gain-of-function Approach to Investigate Early Cell Fate Determinants in Preimplantation Mouse Embryos
Published on: June 6, 2016
Molecular and ultrastuctural changes of rat pre-implantation embryos during two-cell developmental arrest
Background:
Rat pre-implantation embryos often suffer 2-cell stage developmental arrest and fail to progress further under in-vitro conditions.
Objective:
In order to understand underlying mechanism leading to 2-cell arrest, we investigated the molecular changes, culture conditions and subcellular changes.
Methods:
Gene expression in in-vivo developed 2-cell embryos (in-vivo), in- vitro developed 2-cell embryos (in-vitro), and in-vitro 2-cell arrested embryos (arrested) were investigated using microarrays and real-time PCR. Ultra-structural changes were determined using electron microscopy.
Results:
Gene expression was similar between in-vivo and in-vitro embryos. Over 2400 genes changed in arrested embryos compared to in-vivo and in-vitro embryos. The mRNAs encoding proteins involved in translation were elevated in arrested embryos. In-vivo and in-vitro embryos highly expressed genes that were involved in cell cycle, and protein catabolic process compared to arrested embryos. Gene expression data suggested subcellular changes associated with 2-cell block. Transmission electron microscopy showed that in-vivo embryos had healthy subcellular structure, whereas arrested embryos did not have a nuclear membrane, contained small mitochondria and autophagic vacuoles. Furthermore, gene expression data was used for the optimization of culture media conditions to obtain better in-vitro embryonic development. Comparison of five and 20 % oxygen in culture resulted in two times more blastocyst formation with 5 % oxygen.
Conclusions:
These results showed that although all experimental groups appeared morphologically similar, arrested embryos had ultra-structural and molecular changes associated with oxidative stress and apoptosis. In-vitro culture under low oxygen and media additives reduced 2-cell block in rat embryos.
Insights
Rat embryos often arrest at the 2-cell stage in vitro. Optimizing culture conditions, including low oxygen, and adding media supplements can significantly reduce this developmental block.
Area of Science:
- Reproductive biology
- Developmental biology
- Cellular biology
Background:
- Rat pre-implantation embryos commonly exhibit 2-cell stage developmental arrest under in-vitro conditions.
- This arrest prevents further progression, impacting successful in-vitro fertilization and embryo development.
Purpose of the Study:
- To elucidate the molecular mechanisms underlying 2-cell arrest in rat embryos.
- To investigate the roles of molecular changes, culture conditions, and subcellular alterations in this developmental block.
Main Methods:
- Gene expression analysis using microarrays and real-time PCR in in-vivo, in-vitro, and arrested 2-cell embryos.
- Ultra-structural examination of embryos via transmission electron microscopy.
- Optimization of in-vitro culture media, including oxygen levels, to improve embryonic development.
Main Results:
- Gene expression profiles revealed significant molecular differences in arrested embryos compared to normally developing ones, with elevated translation-related mRNAs.
- Arrested embryos displayed abnormal subcellular structures, including absent nuclear membranes and compromised mitochondria, indicative of oxidative stress and apoptosis.
- Lowering oxygen concentration to 5% during in-vitro culture doubled blastocyst formation rates.
Conclusions:
- Despite morphological similarity, arrested rat embryos possess distinct ultra-structural and molecular signatures linked to oxidative stress and apoptosis.
- In-vitro culture modifications, specifically reduced oxygen tension and media additives, effectively mitigate the 2-cell developmental block in rat embryos.
