An investigation of mechanisms underlying mouse blastocyst hatching: a ribonucleic acid sequencing study

Gene expression changes in blastocyst hatching affect embryo implantation success in mice

In mammalian embryonic development, blastocyst hatching is essential for normal implantation and development of the fetus. We reported previously that blastocysts hatching out of the zona pellucida (ZP) exhibited site preferences that were associated with pregnancy outcomes. To characterize these site differences, we analyzed the transcriptomes in the following developing mouse blastocysts within 16 h of hatching: expanding (E), hatching from the A-site (A), B-site (B), and C-site (C), hatched (H), and non-hatching (N). By principal component analysis and hierarchical cluster analysis, we determined that the gene expression profiles of A and B blastocysts, which resulted in good fertility, clustered closely. C and N blastocysts, which resulted in poor fertility, clustered closely, but distantly from A and B. Embryos hatched at B- vs. C-sites, with good vs. poor pregnancy, showed 178 differentially expressed genes (DEGs), mainly involved in immunity, which correlated positively with birth rate. These DEGs were primarily regulated by transcription factors TCF24 and DLX3. During blastocyst hatching, immune-related genes were regulated, such as Ptgs1, Lyz2, Il-α, Cfb (upregulated) and Cd36 (downregulated). By immunofluorescence staining, we found C3 and IL-1β on the extra-luminal surface of the trophectoderm of the hatched blastocyst, suggesting that they play a role in maternal-fetal interactions. As the blastocysts developed from the expanding to the fully hatched state, 307 DEGs were either upregulated by transcription factor ATOH8 or downregulated by SPIC to switch on immune pathways. Based on the hatching outcome, we identified three transcription patterns in developing blastocysts, with complex changes in the transcriptional regulation network of failed hatched blastocysts vs. successfully hatched blastocysts. We developed a LASSO regression-based model using DEGs Lyz2, Cd36, Cfb, and Cyp17a1 to predict implantation success. This study revealed the diverse, multidimensional developmental fates of blastocysts during short-term hatching and indicated that the immune properties of the embryo had a major effect on blastocyst hatching outcomes. We suggest that transcriptional changes and their regulation during the development of the preimplantation blastocyst affect implantation. This study contributes to our understanding of the role of transcriptional changes in mammalian embryonic development during hatching and their effect on maternal-fetal interactions.

Estrogen signaling encourages blastocyst development and implantation potential

PURPOSE

Estrogen is well-known for preparing uterine receptivity. However, its roles in regulating embryo development and implantation are unclear. Our objective was to characterize estrogen receptor 1 (ESR1) in human and mouse embryos and determine the effect of estradiol (E2) supplementation on pre- and peri-implantation blastocyst development.

METHODS

Mouse embryos, 8-cell through hatched blastocyst stages, and human embryonic days 5-7 blastocysts were stained for ESR1 and imaged using confocal microscopy. We then treated 8-cell mouse embryos with 8 nM E2 during in vitro culture (IVC) and examined embryo morphokinetics, blastocyst development, and cell allocation into the inner cell mass (ICM) and trophectoderm (TE). Finally, we disrupted ESR1, using ICI 182,780, and evaluated peri-implantation development.

RESULTS

ESR1 exhibits nuclear localization in early blastocysts followed by aggregation, predominantly in the TE of hatching and hatched blastocysts, in human and mouse embryos. During IVC, most E2 was absorbed by the mineral oil, and no effect on embryo development was found. When IVC was performed without an oil overlay, embryos treated with E2 exhibited increased blastocyst development and ICM:TE ratio. Additionally, embryos treated with ICI 182,780 had significantly decreased trophoblast outgrowth during extended embryo culture.

CONCLUSION

Similar ESR1 localization in mouse and human blastocysts suggests a conserved role in blastocyst development. These mechanisms may be underappreciated due to the use of mineral oil during conventional IVC. This work provides important context for how estrogenic toxicants may impact reproductive health and offers an avenue to further optimize human-assisted reproductive technology (ART) to treat infertility.