A novel microfluidics-based device achieves automatic cumulus cells removal and optimal embryo development in cattle

Oocyte or zygote denudation is a procedure required for optimal visualization of the oocyte or the developing embryo. Cumulus cells are conventionally removed by mechanical and/or enzymatic treatment, a manual procedure prone to operator-to-operator variations in completeness of denudation and shear force applied. We have developed an automated denudation prototype based on microfluidics able to denude 16 bovine cumulus oocyte complexes (COCs) at a time. COCs matured and fertilized in vitro were randomly allocated into two groups: one was denuded by manual stripping and other was denuded using the automatic denudation prototype. A zona pellucida permeability test observed that zonae were permeable to 20 nm particles and impermeable to 40 and 100 nm, irrespective of the denudation protocol employed. Blastocyst formation rates were similar between both protocols, and no differences were observed in the total, inner cell mass and trophectoderm cell numbers at the blastocyst stage. Blastocyst transcriptome was remarkably similar between both denudation groups, with only three genes being differentially expressed. In contrast, 36 and 48 genes were differentially expressed between in vivo derived blastocysts and in vitro produced blastocysts following automatic and manual denudation, respectively. Finally, an in vitro analysis of post-hatching developmental ability revealed similar survival, hypoblast migration and embryonic disc formation rates between embryos obtained following manual or automatic denudation. In conclusion, the device possibilities a safe and repeatable means to denude bovine COCs and constitutes a first step to attain automatic denudation in human COCs, whose size is remarkably similar to those of cattle.