Evaluate the developmental competence of human 8-cell embryos by single-cell RNA sequencing.

Abstract: The transition of maternal to zygotic gene expression regulation is critical for human preimplantation embryo development. In recent years, single-cell RNA sequencing (scRNA-seq) had been applied to detect the factors that regulate human oocyte maturation and early embryo development. Here, the evaluation of transcriptomes in single blastomere from the embryo collected from patients by scRNA-seq was performed. There were 20 blastomeres biopsied from 8-cell embryos of seven patients who received more than two ART cycles due to low embryo competence. Meanwhile, ten cells were collected from 8-cell embryos of four patients who received ART treatment due to male or tubal factors. The blastomeres were then evaluated using the previously established scRNA-seq method to determine the associations between their gene expression and developmental competence. The total number of genes detected in 8-cell embryos that failed to form blastocyst including maternal and zygotic mRNAs was reduced. There were 324 differently expressed genes detected among the 8-cell embryos including 65 genes that were significantly suppressed in the 8-cell embryos that failed to form blastocyst. Further analysis found these 8-cell embryos arrested at the cleavage stage due to the dysfunction of the cell cycle, DNA transcription activity, histone methylation, and cell division-related genes such as SMCO-1, ZNF271P,ZNF679, ASF1b, BEX3, DPPA2, and ORC4. The alterations of gene expression detected in human 8-cell embryos are tightly associated with its developmental competence and could be used as targets to enhance embryo development or parameters to predict the embryo's development outcomes.

Lay summary: Many females are suffering infertility due to the failure of embryonic development at early stages due to unknown causes. At the very beginning of human embryo development, the embryos start to express its own genes, which should be achieved at 8-cell stage. In current research, we isolated one cell from 8-cell embryos and detected the gene expression at single-cell level. Then the remaining cells of these embryos were cultured to form blastocyst. Meanwhile, the data was analyzed according to the outcomes of embryo development. We detected 324 differently expressed genes between the 8-cell embryos that succeeded and failed to form blastocyst. Our research showed the association between the gene expression and the developmental competence of 8-cell embryos. The findings could be used to predict the embryo quality and potential therapy target to improve the efficiency of assisted reproductive techniques.