No abstract

This study aimed to investigate the effects of different concentrations of N-acetylcysteine (NAC) on the growth, antrum formation, viability, and ultrastructure of bovine secondary follicles cultured in vitro for 18 days. To this end, the follicles were cultured in TCM-199+ medium alone or supplemented with 1.0, 5.0, or 25.0 mM NAC. Follicular growth, antrum formation, viability (calcein-AM and ethidium homodimer-1) and ultrastructure were evaluated at the end of culture period. The results showed that 1.0 mM NAC increased the percentage of growing follicles and the fluorescence intensity for calcein-AM when compared to other treatments (p < 0.05). On the other hand, follicles cultured with 25.0 mM NAC had higher fluorescence intensity for ethidium homodimer-1, which is a sign of degeneration. Ultrastructural analysis showed that oocytes from follicles cultured in control medium alone or with 1 mM NAC had intact zonae pellucidae in close association with oolemmae, but the ooplasm showed mitochondria with a reduced number of cristae. On the other hand, oocytes from follicles cultured with 5 or 25 mM NAC had extremely vacuolated cytoplasm and no recognizable organelles. In conclusion, 1 mM NAC increases cytoplasmic calcein staining and the growth rate in bovine secondary follicles cultured in vitro, but the presence of 5 or 25 mM NAC causes damage in cellular membranes and organelles, as well as reducing the percentages of growing follicles.

Summary This study aims to evaluate the effects of N-acetylcysteine (NAC) on bovine oocyte maturation, mitochondrial activity and transzonal projections (TZP), as well as on the levels of reactive oxygen species (ROS) and messenger RNA (mRNA) for catalase (CAT) superoxide dismutase (SOD), periredoxin-6 (Prdx6), glutathione peroxidase (GPx), growth and differentiation factor-9 (GDF9), histone H1Foo, cyclin B1 (CCNB1) and c-Mos. Bovine cumulus–oocyte complexes (COC) of medium-sized antral follicles (3.0–6.0 mm) were prematured in TCM-199 for 8 h at 38.5°C in 5% CO2. After prematuration in the presence of forskolin and C-type natriuretic peptide, COCs were matured in TCM-199 alone or with 0.1, 0.5 or 2.5 mM NAC. Then, oocytes were classified according to the stage of chromatin. Furthermore, mitochondrial activity and intracellular levels of ROS and TZP were also evaluated. The levels of mRNAs for CAT, SOD, Prdx6, GPx, GDF9, H1Foo, CCNB1 and c-Mos were evaluated using real-time polymerase chain reaction (RT-PCR). The results showed that NAC significantly increased the percentages of oocytes with resumption of meiosis when compared with those oocytes matured in control medium. Oocytes had homogeneous mitochondrial distribution, and those cultured with 0.1 and 0.5 mM NAC had lower levels of ROS when compared with the control. In addition, 0.5 mM NAC reduced TZP and the levels of mRNA for CCNB1. In contrast, NAC did not influence the expression of CAT, GPx, Prdx6, SOD, GDF9, H1Foo, and c-Mos. In conclusion, 0.5 mM NAC reduced the levels of ROS, TZP and mRNA for CCNB1, and improved in vitro resumption of meiosis in oocytes from medium-sized bovine antral follicles.

The aims of this study were to evaluate the effects of epidermal growth factor (EGF) and progesterone (P4) on maturation and expression transcripts for GDF9, CCNB1, H1FOO, cMOS, PARN, and eIF4E after prematuration of cumulus-oocyte complexes (COCs) from antral follicles. Bovine COCs (3-6mm) were aspirated and pre-matured for 20h in control medium [TCM-199 containing 5.0mgmL−1 LH, 0.5mgmL−1 FSH, 0.4% bovine serum albumin, cilostamide (10μM) and follicular hemisections] alone or supplemented with EGF (10ngmL−1), P4 (100 µM), or both EGF (10ngmL−1) and P4 (100 µM). After that, COCs were matured for 24h in the same medium, without EGF, P4, cilostamide, and follicular hemisections. Oocyte diameters were evaluated with the software Nis Elements (Nikon Instruments Inc.). To evaluate meiotic progression, the oocytes were fixed in 4% paraformaldehyde and transferred to 0.5% Triton X-100. The chromatin configuration during meiosis was assessed by 10μgmL−1 bisbenzimide (Hoechst 33342) and analysed under an epi-fluorescent inverted microscope (DMI4000B; Leica). Oocytes were classified according to the nuclear maturation stage as germinal vesicle, metaphase I, anaphase I, telophase I, and metaphase II. To evaluate mRNA expression, oocytes were stored in micr-centrifuge tubes at −80°C until RNA extraction. RNA was extracted using Trizol according to the manufacturer's instructions (Invitrogen). After reverse transcription, mRNA for GDF9, cyclin B1, H1FOO, cMOS, PARN, eIF4E, and GAPDH (housekeeping gene) was quantified by real-time PCR and analysed by Kruskal-Wallis test. The percentages of oocytes in each stage of maturation were compared by Mann-Whitney test (P&lt;0.05). The results showed that prematuration of COCs in the presence of P4 and both EGF and P4 promoted an increase in oocyte diameter compared with the control or EGF treatment alone. The presence of cilostamide inhibited early meiotic resumption, benefiting oocyte capacitation, but the presence of EGF, P4, or EGF and P4 together in the prematuration medium did not influence meiosis resumption rates. The presence of EGF or P4 in prematuration medium increased the mRNA levels for cMOS in oocytes (P&lt;0.05). The H1FOO mRNA levels in oocytes cultured with EGF and P4 increased significantly compared with oocytes cultured in EGF alone (P&lt;0.05). In contrast, mRNA levels for cyclin B1 in oocytes cultured with P4 were higher than those cultured in the presence of EGF alone (P&lt;0.05). In addition, levels of mRNA for eIF4E showed a significant reduction in oocytes cultured with P4 compared with those pre-matured with EGF or both EGF and P4. The EGF treatment reduced the levels of mRNA for GDF9 compared with control medium. The mRNA levels of PARN did not differ significantly between treatments. In conclusion, EGF, P4, and EGF and P4 combined did not influence oocyte growth and meiotic resumption. However, EGF or P4 increased the mRNA expression of cMOS, whereas EGF reduced the levels of transcripts for GDF9.