LncRNA-mediated effects of vitrification temperatures and cryoprotectant concentrations on bovine oocyte development following vitrification at the GV stage

We evaluated the effects of different vitrification temperatures (VTs) and cryoprotective agent concentrations (CPAs) on the viability and expressions of long non-coding RNA (lncRNA) in bovine oocytes following vitrification at the germinal vesicle (GV) stage. Our findings provide a theoretical support for improvement of the cryopreservation technology of bovine immature oocytes (BIOs). Bovine cumulus oocyte complexes (COCs) were collected and randomized into five groups: fresh oocytes (control), oocytes vitrified in liquid helium (LHe; -269 °C) with 5.6 M CPAs (LHe 5.6 M), oocytes vitrified in LHe with 6.6 M CPAs (LHe 6.6 M), oocytes vitrified in liquid nitrogen (LN; -196 °C) with 5.6 M CPAs (LN 5.6 M), and oocytes vitrified in LN with 6.6 M CPAs (LN 6.6 M). Of the four vitrification groups, the LHe 5.6 M group exhibited the highest blastocyst rate (13.22%), followed by the LHe 6.6 M group (10.19%) and LN 6.6 M group (9.77%), while the LN 5.6 M group had the lowest blastocyst rate (1.87%). Then, lncRNA expressions in the five groups were profiled. A total of 18,271 lncRNAs were identified, of which 2,158 were differentially expressed lncRNAs (DELs) in the vitrified groups, compared to the fresh group (P < 0.05; fold-change > 2). Co-location (cis) and co-expression (trans) prediction revealed 14 differentially expressed target genes (DETGs), which corresponded to 17 DELs. Based on grouping data and expression profiles of the DELs, we demonstrated that different VTs (-269 °C vs. -196 °C) can affect the expressions of MSTRG.12295.5, MSTRG.37123.1, MSTRG.37930.2, MSTRG.40464.9, MSTRG.8869.3 and MSTRG.26680.6. Expressions of these lncRNAs were affected by CPAs only in the condition of vitrification with LHe (-269 °C). Expressions of MSTRG.35129.6 were associated with exposures to both VTs and CPAs; while expressions of MSTRG.3578.3, MSTRG.40576.3, MSTRG.6723.5, MSTRG.32862.4, MSTRG.1184.4, MSTRG.33110.3, MSTRG.40454.2, MSTRG.41073.2, MSTRG.44732.4 and MSTRG.6729.3 might be related to vitrification. Co-expression analysis showed that MSTRG.12295.5, MSTRG.37930.2, MSTRG.40454.2, MSTRG.8869.3 and MSTRG.6723.5 expressions affect oocyte development after vitrification by regulating target gene expressions. Taken together, improvement of the developmental ability of BIOs after LHe vitrification maybe attributed to changes in expressions of some lncRNAs. Our findings elucidate on the molecular mechanisms underlying the development of BIOs under different VTs and CPAs.