Cumulus cell (CC) expansion is pivotal for oocyte maturation, during which CCs release factors that initiate paracrine signaling within the follicular fluid (FF). The FF is abundant in extracellular vesicles (EVs) that facilitate intercellular communication. Although bovine and murine EVs can control cumulus expansion, these effects have not been observed in equines. This study aimed to assess the impact of FF-derived EVs (ffEVs) on equine CC expansion, viability, and transcriptome. Cumulus–oocyte complexes (COCs) that underwent in vitro maturation (IVM) in the presence (200 µg protein/mL) or absence (control) of ffEVs were assessed for cumulus expansion and viability. CCs were isolated after 12 h of IVM, followed by RNA extraction, cDNA library generation, and subsequent transcriptome analysis using next-generation sequencing. Confocal microscopy images illustrated the internalization of labeled ffEVs by CCs. Supplementation with ffEVs significantly enhanced cumulus expansion in both compacted (Cp, p < 0.0001) and expanded (Ex, p < 0.05) COCs, while viability increased in Cp groups (p < 0.01), but decreased in Ex groups (p < 0.05), compared to the controls. Although transcriptome analysis revealed a subtle effect on CC RNA profiles, differentially expressed genes encompassed processes (e.g., MAPK and Wnt signaling) potentially crucial for cumulus properties and, consequently, oocyte maturation.

Some human, bovine, and mouse in vitro fertilized (IVF) embryos with morphokinetic abnormalities such as fragmentation, direct cleavage, and cytoplasmic vacuoles have the potential to reach the blastocyst stage, which is related to a high potential for implantation. The latest techniques of embryo development observation to enable the evaluation and selection of embryos are based on time lapse monitoring (TLM). The aim of this study was to determine the frequency of morphological defects in feline embryos, their competence to reach the blastocyst stage, and their ability to hatch. Oocyte-cumulus complexes were isolated after the scarification of ovaries and matured in vitro. Matured oocytes were fertilized in vitro by capacitated spermatozoa. Randomly selected oocytes were observed by TLM for seven-to-eight days. Out of 76 developed embryos, 41 were morphologically normal, of which 15 reached the blastocyst stage. Of 35 abnormally developed embryos, 17 reached the blastocyst stage, of which six had single aberrations and 11 had multiple aberrations. The hatching rate (%) was 15.6% in normally cleaving embryos, 6.25% in embryos with single aberrations, and 3.33% in those with multiple aberrations. The present study reports the first results, found by using TLM, about the frequency of the morphological defects of feline embryos, their competence to reach the blastocyst stage, and their ability to hatch.

The aim of this study was to analyze the morphokinetic parameters of feline embryos using a time lapse system. Oocytes matured in vitro were fertilized (IVF) and in vitro cultured in a time lapse-system (Primo Vision^®, Gothenburg, Sweden). The first cell division of embryos occurred between 17 h post insemination (hpi) and 38 hpi, with the highest proportion of embryos (46%) cleaving between 21 and 24 hpi. The timing of the first cleavage significantly affected further embryo development, with the highest development occurring in embryos that cleaved at 21–22 hpi. Embryos that cleaved very early (17–18 hpi) developed poorly to the blastocyst stage (2%) and none of the embryos that cleaved later than 27 hpi were able to reach the blastocyst stage. Morphological defects were observed in 48% of the embryos. There were no statistically significant differences between the timing intervals of the first cleavage division and the frequency of morphological defects in embryos. Multiple (MUL) morphological defects were detected in more than half (56%) of the abnormal embryos. The most frequent single morphological defects were cytoplasmic fragmentation (FR) (8%) and blastomere asymmetry (AS) (6%). Direct cleavage (DC) from 1–3 or 3–5 blastomeres, reverse cleavage (RC) and vacuoles were rarely observed (2–3%). The timing of blastocyst cavity formation is a very good indicator of embryo quality. In our study, blastocyst cavity formation occurred between 127–167 hpi, with the highest frequency of hatching observed in blastocysts that cavitated between 142–150 hpi. Blastocysts in which cavitation began after 161 h did not hatch. In conclusion, the timing of the first and second cleavage divisions, the timing of blastocyst cavity formation and morphological anomalies can all be used as early and non-invasive indicators of cat embryo development in vitro.

The present experiment employed time-lapse (TL) imaging to assess the effects of vitrification on the development of ovine blastocysts and to see if the timing of blastocyst formation and expansion was correlated with the numbers of embryo- and trophoblasts determined through differential staining of the expanded blastocysts. Ovaries were obtained after slaughter from cycling (October-March) Polish Longwool ewes aged 1-3 years and cumulus-oocyte complexes were collected by ovarian scarification. In vitro maturation was performed in TCM 199 medium supplemented with Earle's Salt, 10% of FBS, and 5 μg/mL of LH/FSH at 38 °C for 24 h. After maturation, the oocytes were incubated with thawed ram semen (IVF) for 19 h and all presumptive zygotes were transferred to a 16-well dish containing Cult medium for monitoring with the Primo Vision TL system. A portion of ovine embryos were vitrified (Cryotop system) at the early cavitation stage and TL observations of warmed (n = 30) and non-vitrified (n = 32) blastocysts continued until the attainment of the expanded blastocyst stage, at which point they were differentially stained with bisbenzimide and propidium iodide for microscopic enumeration of embryoblasts (inner cell mass blastomeres) and trophoblast-cells. There were no statistically significant differences in the timing of blastulation (tB) and formation of expanded blastocysts (tEB) between vitrified and non-vitrified ovine embryos, but non-vitrified blastocysts exceeded (P < 0.05) their vitrified and warmed counterparts in the mean number of embryo- and trophoblasts. In addition, the number of trophoblasts was negatively and moderately correlated with tB and tEB, for both vitrified and non-vitrified embryos. It can be concluded that even though vitrification of ovine embryos is associated with a significant reduction in the number of blastomeres, the rate of blastocyst development remains closely linked to the numbers of trophoblastic cells.