Developmental consequences of alternative Bcl‐x splicing during preimplantation embryo development

Abstract

Elevated cell death in human preimplantation embryos is one of the cellular events compromising pregnancy rates after assisted reproductive technology treatments. We therefore explored the molecular pathways regulating cell death at the blastocyst stage in human embryos cultured in vitro. Owing to limited availability of human embryos, these pathways were further characterized in mouse blastocysts. Gene expression studies revealed a positive correlation between the cell death index and the expression of Bcl‐x transcript. Cell death activation in human blastocysts was accompanied by changes in Bcl‐x splicing, favoring production of Bcl‐xS, an activator of cell death. Expression of Bcl‐xS was detected in a subset of human blastocysts that show particular clustering in dying and/or dead cells. Altering the Bcl‐xL/Bcl‐xS ratio in mouse embryos, in antisense experiments, confirmed that upregulation of Bcl‐xS, with concomitant downregulation of Bcl‐xL, compromised developmental potential and committed a subset of cells to undergoing cell death. This was accompanied by increased accumulation of reactive oxygen species levels without any impact on mtDNA content. In addition, altered Bcl‐x splicing in favor of Bcl‐xS was stimulated by culture in HTF medium or by addition of excessive glucose, leading to compromised embryo development. Thus, we conclude that inappropriate culture conditions affect Bcl‐x isoform expression, contributing to compromised preimplantation embryo development.

Insulin-like growth factor 2: A modulator of anti-apoptosis related genes (HSP70, BCL2-L1) in bovine preimplantation embryos

“…Accordingly, several studies have shown an important role of BCL2-L1 in the regulation of embryonic cell death in pig [18,34,35,41], mouse [42], human [43], and cattle [44][45][46]. In contrast, some studies have shown that the levels of BCL2-L1 transcripts did not correlated with blastocyst quality [47,48].…”

NLRP5 Mediates Mitochondrial Function in Mouse Oocytes and Embryos1

“…The standard concentration of the generated pTOPO-Mito was quantitated using nanodrop and utilized in qPCR. Mitochondrial DNA copy number in single oocytes was determined as previously described [36].…”

Involvement of BCL2 family members in the regulation of human oocyte and early embryo survival and death: gene expression and beyond

“…The transcription of the BAX homolog BAK and the BH3-only member HRK appears to be up-regulated in fragmenting embryos at the four-cell stage (Jurisicova et al 2003, Metcalfe et al 2004, suggesting a potential role for these proapoptotic members in regulating embryonic death and fragmentation in a redundant manner to BAX or upstream of BAX, respectively. Furthermore, an alternative splicing of the BCL2L1 gene in favor of the short proapoptotic isoform BCL2L1S was observed in a subset of human and mouse fragmented and/or dying embryos (Jurisicova et al 1998, Perumalsamy et al 2010, suggesting that subtle post-transcriptional modifications could be implemented to regulate embryonic fate. Accordingly, decreasing the BCL2L1L/BCL2L1S ratio in mouse embryos by using an antisense strategy that up-regulates BCL2L1S and concomitantly downregulates BCL2L1L has severely affected embryonic developmental competence (Perumalsamy et al 2010).…”

“…Furthermore, an alternative splicing of the BCL2L1 gene in favor of the short proapoptotic isoform BCL2L1S was observed in a subset of human and mouse fragmented and/or dying embryos (Jurisicova et al 1998, Perumalsamy et al 2010, suggesting that subtle post-transcriptional modifications could be implemented to regulate embryonic fate. Accordingly, decreasing the BCL2L1L/BCL2L1S ratio in mouse embryos by using an antisense strategy that up-regulates BCL2L1S and concomitantly downregulates BCL2L1L has severely affected embryonic developmental competence (Perumalsamy et al 2010). …”