Domestic cat embryos generated without zona pellucida are capable of developing in vitro but exhibit abnormal gene expression and a decreased implantation rate

Proteomic Analysis of Domestic Cat Blastocysts and Their Secretome Produced in an In Vitro Culture System without the Presence of the Zona Pellucida

Domestic cat blastocysts cultured without the zona pellucida exhibit reduced implantation capacity. However, the protein expression profile has not been evaluated in these embryos. The objective of this study was to evaluate the protein expression profile of domestic cat blastocysts cultured without the zona pellucida. Two experimental groups were generated: (1) domestic cat embryos generated by IVF and cultured in vitro (zona intact, (ZI)) and (2) domestic cat embryos cultured in vitro without the zona pellucida (zona-free (ZF group)). The cleavage, morula, and blastocyst rates were estimated at days 2, 5 and 7, respectively. Day 7 blastocysts and their culture media were subjected to liquid chromatography-tandem mass spectrometry (LC-MS/MS). The UniProt Felis catus database was used to identify the standard proteome. No significant differences were found in the cleavage, morula, or blastocyst rates between the ZI and ZF groups (p > 0.05). Proteomic analysis revealed 22 upregulated and 20 downregulated proteins in the ZF blastocysts. Furthermore, 14 proteins involved in embryo development and implantation were present exclusively in the culture medium of the ZI blastocysts. In conclusion, embryo culture without the zona pellucida did not affect in vitro development, but altered the protein expression profile and release of domestic cat blastocysts.

Zona pellucida removal modifies the expression and release of specific microRNAs in domestic cat blastocysts

The in vitro culture of domestic cat embryos without the zona pellucida affects their implantation capacity. MicroRNAs (miRNAs) have an important role in embryo-maternal communication and implantation. The objective of this study was to evaluate the expression of specific miRNAs in domestic cat blastocysts cultured without the zona pellucida. Two experimental groups were done: (1) domestic cat embryos cultured with the zona pellucida (zona intact control group, ZI); and (2) cultured without the zona pellucida (zona free group, ZF). The cleavage, morula and blastocyst rates were evaluated. The blastocysts and their spent medium were used for miRNA expression analysis using RT-qPCR (miR-21, miR-24, mi25, miR-29, miR-96, miR-98, miR-103, miR-191, miR-196, miR-199, miR-130, miR-155 and miR-302). The pre-mature microRNAs (pre-miRNAs) and miRNAs were evaluated in the blastocysts and only miRNAs were evaluated in the spent medium. No differences were observed in the cleavage, morula and blastocyst rates between the ZF and ZI groups (P > 0.05). For miRNAs analysis, miR-103 and miR-191 had the most stable expression and were selected as internal controls. ZF blastocysts had a higher expression of miR-21, miR-25, miR-29 and miR-199 and a lower expression of miR-96 than their ZI counterparts (P < 0.05). Furthermore, higher levels of miR-21, miR-25 and miR-98 were detected in the spent medium of ZF blastocysts (P < 0.05). In conclusion, in vitro culture of domestic cat embryos without the zona pellucida modifies the expression of miR-21, miR-25, miR-29, miR-199 and miR-96 at the blastocyst stage and the release of miR-21, miR-25 and miR-98.

Analysis of trophectoderm markers in domestic cat blastocysts cultured without zona pellucida

Domestic cat embryos generated by in vitro fertilization (IVF) and cultured without the zona pellucida have a reduced implantation capacity after embryo transfer at the blastocyst stage. The objective of this study was to evaluate the expression of trophectoderm markers in domestic cat blastocysts cultured without the zona pellucida. Two experimental groups were selected: (1) domestic cat embryos generated by IVF and cultured in vitro normally (zona intact group, ZI); and (2) domestic cat embryos generated by IVF and cultured in vitro without a zona pellucida (zona-free group, ZF). In the ZF group, the zona pellucida of the presumptive zygote was removed and these were cultured using the well of the well (WOW) system. In vitro culture was carried out for 7 days. The cleavage, morula and blastocyst rates were estimated. Finally, the relative expression levels of the trophectoderm markers TEAD4, YAP1, CDX2 and EOMES, the cell adhesion marker E-cadherin and the apoptosis marker CASP3 were evaluated by RT-qPCR in the blastocysts. The Wilcoxon test was used to evaluate differences (P < 0.05). No differences were observed in the cleavage, morula and blastocyst rates between the ZF and ZI groups. No differences were found in the expression of TEAD4, CDX2, E-cadherin and CASP3 between groups. The expression of YAP1 and EOMES was higher in ZF blastocysts than in ZI blastocysts. In conclusion, the in vitro culture without the zona pellucida generates an overexpression of YAP1 and EOMES in the domestic cat blastocysts. More studies are needed to confirm if this overexpression might affect in vivo development.

Zona pellucida removal by acid Tyrode's solution affects pre- and post-implantation development and gene expression in mouse embryos

The zona pellucida (ZP) plays a crucial role in the process of fertilization to early embryonic development, including cellular arrangement and communication between blastomeres. However, little is known regarding the role of the ZP in pre- and post-implantation embryonic development associated with gene expression. We investigated the effect of zona pellucida removal (ZPR) on pre- and post-implantation development of mouse embryos. After ZPR of 2-cell stage embryos was performed by acid Tyrode's solution, which is commonly used for ZP treatment, compaction occurred earlier in ZP-free (ZF) than ZP-intact (ZI) embryos. In addition, the expression of differentiation-related genes in the inner cell mass (ICM) and trophectoderm (TE) was significantly altered in ZF blastocyst compared with ZI embryos. After embryo transfer, the rate of implantation and live fetuses was lower in ZF embryos than in control embryos, whereas the fetal weight at E17.5 was not different. However, placental weight significantly increased in ZF embryos. RNA-seq analysis of the placenta showed that a total of 473 differentially expressed genes (DEGs) significantly influenced the biological process. The present study suggests that ZPR by acid Tyrode's solution at the 2-cell stage not only disturbs the expression pattern of ICM/TE-related genes but affects the post-implantation development of mouse embryos. Overall, this study provides deeper insight into the role of the ZP during early embryonic development and the viability of post-implantation development.