Nuclear and mitochondrial DNA in blastocoele fluid and embryo culture medium: evidence and potential clinical use

Abstract

The ability to screen embryos for aneuploidy or inherited disorders in a minimally invasive manner may represent a major advancement for the future of embryo viability assessment. Recent studies have demonstrated that both blastocoele fluid and embryo culture medium contain genetic material, which can be isolated and subjected to downstream genetic analysis. The blastocoele fluid may represent an alternative source of nuclear DNA for aneuploidy testing, although the degree to which the isolated genetic material is solely representative of the developing embryo is currently unclear. In addition to nuclear DNA, mitochondrial DNA (mtDNA) can be detected in the embryo culture medium. Currently, the origin of this nuclear and mtDNA has not been fully evaluated and there are several potential sources of contamination that may contribute to the genetic material detected in the culture medium. There is however evidence that the mtDNA content of the culture medium is related to embryo fragmentation levels and its presence is predictive of blastulation, indicating that embryo development may influence the levels of genetic material detected. If the levels of genetic material are strongly related to aspects of embryo quality, then this may be a novel biomarker of embryo viability. If the genetic material does have an embryo origin, the mechanisms by which DNA may be released into the blastocoele fluid and embryo culture medium are unknown, although apoptosis may play a role. While the presence of this genetic material is an exciting discovery, the DNA in the blastocoele fluid and embryo culture medium appears to be of low yield and integrity, which makes it challenging to study. Further research aimed at assessing the methodologies used for both isolating and analysing this genetic material, as well as tracing its origin, are needed in order to evaluate its potential for clinical use. Should such methodologies prove to be routinely successful and the DNA recovered demonstrated to be embryonic in origin, then they may be used in a minimally invasive and less technical methodology for genetic analysis and embryo viability assessment than those currently available.

Karyotype of the blastocoel fluid demonstrates low concordance with both trophectoderm and inner cell mass

“…The presence of embryonic DNA in BF suggest that potential mechanisms might exist by which the genetic material is released into the blastocoel cavity, like cell lysis, apoptosis and elimination of cellular debris (34). Interestingly, the intact ICM karyotype in the presence of aneuploidy in BF-DNA in some of the embryos also seems to support the idea that aneuploid cells are progressively depleted from the developing embryo through apoptosis, ensuring the genomic integrity of the future fetus (35).…”

Chromosomal analysis in IVF: just how useful is it?

“…Such an approach avoids the need for embryo biopsy which, as indicated earlier, has the potential to damage the embryo. Nevertheless, there are several potential sources of contamination that may contribute to the genetic material detected in the culture medium (Hammond et al 2016) and before it is put into full clinical use, it needs to be validated against 'gold standard' approaches.…”

Non-invasive preimplantation genetic screening using array comparative genomic hybridization on spent culture media: a proof-of-concept pilot study

“…Similar to blastocoel fluid, embryo culture medium was suggested to harbour DNA that can be used for further analysis (Palini et al, 2013;Scaruffi et al, 2011). Therefore, the possibility of non-invasive preimplantation genetic screening (PGS) was discussed as a potential future technique for embryo assessment (Cohen et al, 2013;Hammond et al, 2016;Lu et al, 2016).…”