IVM media, oocyte diameter and donor genotype at RYR1 locus in relation to the incidence of porcine diploid oocytes after maturation in vitro

Altered microfilament dynamics contribute to the formation of diploid metaphase spindles in porcine oocytes which fail to reach the metaphase-II stage during in vitro maturation

Premature meiotic arrest during in vitro maturation (IVM) of porcine oocytes after germinal vesicle breakdown is associated with microfilament degradation. We aimed to clarify (1) if such arrest occurs at the metaphase-I (MI) stage or the oocyte progresses to a so-called diploid metaphase-II (MII) stage and (2) if microfilament degradation is the cause or result of the meiotic arrest. The number and morphology of chromosomes in oocytes showing premature meiotic arrest at 44 h IVM (38 monovalents) was similar to those cultured in the presence of the actin polymerization-inhibitor cytochalasin-B, but different from those of MI-stage (19 bivalents), and MII-stage oocytes (19 monovalents) at 33 and 44 h of IVM, respectively. Immunostaining revealed similar frequencies of microfilament degradation in prematurely arrested and cytochalasin-B-treated oocytes (58.7% and 57.2%, respectively), which were higher (P < 0.05) than those in MI- and MII-stage oocytes (10.6% and 6.8%, respectively). Induction of MI-arrest by nocodazole did not affect microfilament morphology. ATP and mRNA levels of microfilament-related genes in oocytes were similar among all groups. These results suggest that altered microfilament dynamics contribute to the formation of diploid metaphase spindles in oocytes, which fail to reach the MII stage. However, the cause of microfilament degeneration remains unclear.

The ND1 and CYTB genes polymorphisms associated with in vitro early embryo development of Sanjabi sheep

This study aimed to investigate the association between polymorphisms of ND1 and CYTB genes and in vitro early embryo development of Sanjabi sheep. Blood and ovarian samples were collected from a local slaughterhouse. The cumulus-oocyte complexes with a diameter greater than 3 mm were aspirated from follicles, and in vitro maturation (IVM) and in vitro culture (IVC) rates of them were recorded. A respective 1200 bp and 980 bp fragments of ND1 and CYTB genes were genotyped using a modified single strand conformation polymorphism (SSCP) method. The results of this study revealed that four different patterns, named as A, B, C, and D were observed for both ND1 and CYTB genes. The ND1 gene polymorphisms had significant effects on the IVM and IVC rate (p < 0.05). The pattern C of the ND1 gene significantly increased the IVM rate compared to the patterns A, B and D. For the IVC, the highest and lowest means were related to the C and B patterns, respectively. The CYTB gene polymorphisms also had significant effects on IVC (p < 0.01), but the IVM did not affected (p = 0.07). Here, the pattern D had the highest and the pattern C had the lowest means for both IVM and IVC rates.

The relationship between mitochondrial ND5 gene polymorphisms and in vitro embryo production in Sanjabi sheep

The aim of this study was to investigate mitochondrial ND5 gene polymorphisms and their relationship with in vitro maturation (IVM) and in vitro culture (IVC) of Sanjabi sheep. Blood and ovarian samples of adult ewes were obtained from a local slaughterhouse. For each ovarian sample, cumulus-oocyte complexes larger than 3 mm in diameter were aspirated from follicles, and their IVM and IVC rates were recorded. A 666-bp fragment of the ND5 gene was amplified using the polymerase chain reaction. The samples were genotyped using a modified single-stranded conformation polymorphism (SSCP) method, and an association study was conducted with IVM and IVC rates. Six different SSCP patterns, designated A, B, C, D, E and F with respective frequencies of 8, 47, 4, 4, 32 and 5%, respectively, were observed. According to the results of association analysis, there was no significant association between the ND1 gene polymorphisms and the IVM and IVC rates (P > 0.05).

Effects of oocyte quality, incubation time and maturation environment on the number of chromosomal abnormalities in IVF-derived early bovine embryos

Chromosomal aberrations are one of the major causes of embryo developmental failures in mammals. The occurrence of these types of abnormalities is higher in in vitro-produced (IVP) embryos. The aim of the present study was to investigate the effect of oocyte morphology and maturation conditions on the rate of chromosomal abnormalities in bovine preimplantational embryos. To this end, 790 early cattle embryos derived from oocytes with different morphologies and matured under different conditions, including maturation period (24 v. 36 h) and maturation media (five different serum supplements in TCM-199), were evaluated cytogenetically in three sequential experiments. The rates of normal diploidy and abnormal haploidy, polyploidy and aneuploidy were determined in each embryo. Throughout all the experiments, the rate of chromosomal abnormalities was significantly (P < 0.05) affected by oocyte morphology and maturation conditions (maturation time and culture medium). Lower morphological quality was associated with a high rate of chromosome abnormalities (P < 0.05). Moreover, polyploidy was associated with increased maturation time (P < 0.01), whereas the maturation medium significantly (P < 0.05) affected the rates of haploidy and polyploidy. In general, supplementing the maturation medium with oestrous cow serum or fetal calf serum resulted in higher rates of chromosomal aberrations (P < 0.05) compared with the other serum supplements tested (bovine steer serum, anoestroues cow serum, bovine amniotic fluid and bovine serum albumin). On the basis of the results of the present study, we conclude that the morphological quality of oocytes and the maturation conditions affect the rate of chromosomal abnormalities in IVP bovine embryos.

In vitro production of porcine embryos: current status, future perspectives and alternative applications

The pig is considered to be a suitable source of cells and organs for xenotransplants, as well as a transgenic animal to produce specific proteins, given the biological similarities it shares with human beings. However, the in vitro embryo production system in pigs is inefficient compared with those in other mammals, such as cattle or mice. Although numerous modifications have been applied to improve the efficiency of in vitro embryo production systems in pigs, not much progress has been made to overcome the problem of polyspermy, and low developmental ability due to insufficient cytoplasmic abilities of in vitro matured oocytes and improper culture conditions for the in vitro produced embryos. Recent achievements, such as the establishment of chemically defined medium and utilization of 'zona hardening' technique, have gained some success. However, further research for the reduction of polyspermy and detrimental effects of the culture systems in pigs is still needed.

Gilts and sows produce similar rate of diploid oocytes in vitro whereas the incidence of aneuploidy differs significantly

Oocytes derived from prepubertal gilts show reduced developmental competence when compared to oocytes collected from adult sows. Therefore, the aim of the study was to investigate whether gilts (4-5 months old) and adult sows (average age 3.5 years) of the same breed (Polish Landrace x Polish Large White crossbred) differ with regard to the rate of chromosomally unbalanced oocytes after IVM. COCs derived from individual pairs of slaughterhouse ovaries were matured in vitro and analyzed cytogenetically by conventional staining (Giemsa) and FISH methods (probes corresponding to centromeric regions of pig chromosomes 1 and 10). Altogether, 72 females (31 sows, 41 gilts) and 430 secondary oocytes (194 and 236 oocytes of sows and gilts, respectively) were investigated. Cytogenetic analysis revealed diploid (Giemsa, FISH) and aneuploid (FISH) spreads. The incidence of diploid oocytes was similar for sows (26.0%) and gilts (24.5%) whereas the rate of aneuploid oocytes (nullisomic/disomic) was eight times higher in gilts (10.8%) than in sows (1.3%). Diploid and aneuploid oocytes were observed in 64% of investigated females. Pig chromosome 10 was more frequently disomic/nullisomic compared to chromosome 1 suggesting, that like in human, small porcine chromosomes are often involved in the nondisjunction process. In conclusion, chromosomal imbalance significantly contributes to in vitro embryo production in the pig, since over 60% of females produced diploid or aneuploid gametes. The significantly higher rate of aneuploidy among oocytes derived from gilt ovaries may contribute to the reduced developmental competence of gametes collected from nonmature female pigs.

Supplements to in vitro maturation media affect the production of bovine blastocysts and their apoptotic index but not the proportions of matured and apoptotic oocytes

The objective of this study was to compare the effect of different supplements to the basic IVM medium (TCM199) on the efficiency of cattle oocyte maturation and blastocyst production, and the incidence of apoptosis in both oocytes and blastocysts. Two protein supplements (FBS and fafBSA) and a macromolecule (PVP40) were compared in a 3 treatmentsx9 replicates design. Cumulus-oocyte complexes (COCs) aspirated from slaughterhouse ovaries were matured for 24h in TCM199 medium supplemented with 10% FBS, 6% fafBSA or 4% PVP40 (50-70 COCs in each treatment/replicate), then inseminated and cultured in vitro for 8 days. Immature and mature oocytes as well as Day 8 blastocysts were subjected to TUNEL analysis. Cleavage rate was monitored on Day 2 post-insemination (pi), whereas blastocyst yield on Day 8 pi. The composition of maturation media did not affect zygotic cleavage rate on Day 2 (on average 71.0%), however the blastocyst rate on Day 8 pi was significantly lower (P<0.001) for embryos derived from oocytes matured with PVP40 (16.0%) than for those matured with FBS (22.4%) or fafBSA (22.1%). The rate of TUNEL positive oocytes differed significantly between immature (1.4%) and mature (11.2%) oocytes (P<0.01). Supplements to maturation medium were not related to the incidence of apoptosis in mature oocytes (11.2%) and the rate of oocytes at the second metaphase stage (71.5%). Cumulus cell expansion was reduced by maturation in medium supplemented with PVP40. This macromolecule was also correlated with higher apoptotic index in blastocysts (5.8%) when compared to FBS (3.2%) and fafBSA (3.1%; P<0.001). In conclusion, lower blastocyst rate and elevated apoptotic index in embryos derived from oocytes matured with PVP40 may suggest that synthetic macromolecule provides less balanced environment for oocyte maturation and therefore should be treated with caution.