Single-cell omics, namely single-cell sequencing, was selected as the method of the year in 2013 by Nature Publishing Group (Nawy, 2014). A few years later, a comprehensive transcriptional map of 1529 individual cells from 88 human preimplantation embryos using single-cell RNA-sequencing (RNA-seq) was published (Petropoulos et al, 2016). Here in Geneva Dr Jeroen Krijgsveld presented the first study of single-cell proteome analysis in human oocytes. Single-cell proteome analysis reflects the full content of proteins within the cell, the key determinants of cellular function, and therefore has the best potential for predicting/demonstrating oocyte competence.
Nevertheless, any analysis of the full proteome is a challenging task – the proteome is large and of unknown complexity, and even more on the single cell level because of the limited sample input for mass spectrometry analysis.
It is wonderful to see that Dr Krijgsveld’s group has overcome these limitations by presenting a novel strategy to extract, purify and digest proteins with a novel magnetic bead-based procedure, thereby minimising sample losses and increasing overall sensitivity of detection. As a result, they are now able to routinely detect, identify and quantify around 600 proteins from a single human oocyte. Their comprehensive single-oocyte analysis demonstrates that the proteome composition distinguishes immature oocytes from mature MII oocytes. Furthermore, they showed that oocytes that are matured in vitro in the presence of FSH and HCG and in a co-culture with cumulus cells are more similar to in vivo-matured cells than the cells matured with FSH and HCG only, thus indicating the importance of the ovarian niche during the maturation process. They also demonstrated that, based on the proteome data, co-culture with cumulus cells can be efficiently replaced by addition of the protein vimentin (which is an important component of mesenchymal cells, including granulosa cells).
Altogether, these results indicate that technological advances now enable proteome analysis at the single oocyte level, providing a powerful tool for optimising and improving oocyte maturation procedures.
Signe Altmäe, Junior Deputy SIG Reproductive Genetics
Nawy T. Single-cell sequencing. Nat Methods 2014; 11: 18.
Petropoulos S, Edsgärd D, Reinius B, et al. Single-Cell RNA-Seq Reveals Lineage and X Chromosome Dynamics in Human Preimplantation Embryos. Cell 2016; 165, 1012–26. doi:10.1016/j.cell.2016.03.023