Influence of the duration of gamete interaction on cleavage, growth rate and sex distribution of in vitro produced bovine embryos

Production of sexed bovine embryos in vitro can be improved by selection of sperm treatment and co-culture system

The study investigated the effects of sperm sorting, capacitation treatment and co-cultivation on sexed bovine in vitro embryo production. The effect of treatment and co-culture on production of embryos of the preferred sex from unsorted sperm was also studied. Sperm from five breeding bulls was used for fertilization of mature oocytes as follows: Experiment 1, sorted and unsorted sperm (bulls A-E) treated only with heparin in standard co-cultures; Experiment 2, sorted sperm (bulls A-E) treated with heparin-PHE (penicillamine, hypotaurine, and epinephrine) or heparin-caffeine in drop co-cultures; and Experiment 3, unsorted sperm (bull E) treated with either heparin-PHE or heparin-caffeine in both standard and drop co-cultures. In all bulls, treatment with heparin resulted in significantly (p < .05) reduced cleavage and blastocyst rates from sorted sperm, as compared with those from unsorted sperm. In bulls A, B, D and E, treatment of sorted sperm with heparin-PHE in drops significantly increased the blastocyst rate (p < .05). In unsorted sperm of bull E, heparin-PHE treatment in drops resulted in the XX/XY sex ratio inverse to that obtained by heparin-caffeine treatment in standard co-cultures (32.3%/67.7% and 66.7%/33.3%, respectively). In conclusion, the treatment of sorted sperm with heparin-PHE in modified drop co-cultures can be recommended for production of in vitro sexed embryos. The use of unsorted sperm for production of embryos of the preferred sex by selected capacitation treatment and co-culture can be the method of choice in bulls with low IVF yields from sorted sperm.

Sexual dimorphisms in adult human neural, mesoderm-derived, and neural crest-derived stem cells

Sexual dimorphisms contribute, at least in part, to the severity and occurrence of a broad range of neurodegenerative, cardiovascular, and bone disorders. In addition to hormonal factors, increasing evidence suggests that stem cell-intrinsic mechanisms account for sex-specific differences in human physiology and pathology. Here, we discuss sex-related intrinsic mechanisms in adult stem cell populations, namely mesoderm-derived stem cells, neural stem cells (NSCs), and neural crest-derived stem cells (NCSCs), and their implications for stem cell differentiation and regeneration. We particularly focus on sex-specific differences in stem cell-mediated bone regeneration, in neuronal development, and in NSC-mediated neuroprotection. Moreover, we review our own recently published observations regarding the sex-dependent role of NF-κB-p65 in neuroprotection of human NCSC-derived neurons and sex differences in NCSC-related disorders, so-called neurocristopathies. These observations are in accordance with the increasing evidence pointing toward sex-specific differences in neurocristopathies and degenerative diseases like Parkinson's disease or osteoporosis. All findings discussed here indicate that sex-specific variability in stem cell biology may become a crucial parameter for the design of future treatment strategies.

Effect of spermatozoa motility hyperactivation factors and gamete coincubation duration on in vitro bovine embryo development using flow cytometrically sorted spermatozoa

The aim of the present study was to evaluate the effects of sperm motility enhancers and different IVF times on cleavage, polyspermy, blastocyst formation, embryo quality and hatching ability. In Experiment 1, sex-sorted X chromosome-bearing Bos taurus spermatozoa were incubated for 30 min before 18 h fertilisation with hyperactivating factors, namely 10 mM caffeine (CA), 5 mM theophylline (TH), 10 mM caffeine and 5 mM theophylline (CA + TH); and untreated spermatozoa (control). In Experiment 2, matured B. taurus oocytes were fertilised using a short (8 h) or standard (18 h) fertilisation length, comparing two different fertilisation media, namely synthetic oviducal fluid (SOF) fertilisation medium (SOF-FERT) and M199 fertilisation medium (M199-FERT). Cleavage and blastocyst formation rates were significantly higher in the CA + TH group (77% and 27%, respectively) compared with the control group (71% and 21%, respectively). Cleavage rates and blastocyst formation were significantly lower for the shortest fertilisation time (8 h) in M199-FERT medium (42% and 12%, respectively). The SOF-FERT medium with an 8 h fertilisation time resulted in the highest cleavage rates and blastocyst formation (74% and 29%, respectively). The SOF-FERT medium produced the highest embryo quality (50% Grade 1) and hatching rate (66%). Motility enhancers did not affect polyspermy rates, whereas polyspermy was affected when fertilisation length was extended from 8 h (3%) to 18 h (9%) and in M199-FERT (14%) compared with SOF-FERT (6%). We conclude that adding the motility enhancers CA and TH to sex sorted spermatozoa and Tyrode’s albumin lactate pyruvate (TALP)-Sperm can improve cleavage and embryo development rates without increasing polyspermy. In addition, shortening the oocyte–sperm coincubation time (8 h) resulted in similar overall embryo performance rates compared with the prolonged (18 h) interval.

Random Allocation of Blastomere Descendants to the Trophectoderm and ICM of the Bovine Blastocyst

The first lineage specification during mammalian embryo development can be visually distinguished at the blastocyst stage. Two cell lineages are observed on the embryonic-abembryonic axis of the blastocyst: the inner cell mass and the trophectoderm. The timing and mechanisms driving this process are still not fully understood. In mouse embryos, cells seem prepatterned to become certain cell lineage because the first cleavage plane has been related with further embryonic-abembryonic axis at the blastocyst stage. Nevertheless, this possibility has been very debatable. Our objective was to determine whether this would be the case in another mammalian species, the bovine. To achieve this, cells of in vitro produced bovine embryos were traced from the 2-cell stage to the blastocyst stage. Blastocysts were then classified according to the allocation of the labeled cells in the embryonic and/or abembryonic part of the blastocyst. Surprisingly, we found that there is a significant percentage of the embryos (∼60%) with labeled and nonlabeled cells randomly distributed and intermingled. Using time-lapse microscopy, we have identified the emergence of this random pattern at the third to fourth cell cycle, when cells started to intermingle. Even though no differences were found on morphokinetics among different embryos, these random blastocysts and those with labeled cells separated by the embryonic-abembryonic axis (deviant pattern) are significantly bigger; moreover deviant embryos have a significantly higher number of cells. Interestingly, we observed that daughter cells allocation at the blastocyst stage is not affected by biopsies performed at an earlier stage.

Evaluation of phenotypic, functional and molecular characteristics of porcine mesenchymal stromal/stem cells depending on donor age, gender and tissue source

The biological properties of mesenchymal stem cells (MSCs) are influenced by donor age, gender and/or tissue sources. The present study investigated the cellular and molecular properties of porcine mesenchymal stromal/stem cells (MSCs) isolated from different tissues (adipose & dermal skin) and sex at different ages (1 week & 8 months after birth) with similar genetic and environmental backgrounds. MSCs were analyzed for alkaline phosphatase (AP) activity, CD90 and Oct3/4 expression, in vitro differentiation ability, senescence-associated β-galactosidase (SA-β-Gal) activity, telomeric properties, cell cycle status and expression of senescence (IL6, c-myc, TGFβ, p53 and p21)- and apoptosis (Bak and Bcl2)-related proteins. An age-dependent decline in AP activity and adipogenesis was observed in all MSCs, except for male A-MSCs. CD90 expression did not change, but SA-β-Gal activity increased with advancement in age, except in A-MSCs. Telomeric properties were similar in all MSCs, whereas expression levels of Oct3/4 protein declined with the advancement in age. p21 expression was increased with increase in donor age. Male derived cells have shown higher IL6 expression. The expression of p53 was slightly lower in MSCs of dermal tissue than in adipose tissue. Bak was expressed in all MSCs regardless of age, but up regulation of Bcl2 was observed in DS-MSCs derived at 1 week after birth. In conclusion, adipose tissue-derived MSCs from young female individuals were found to be more resistant to senescence under in vitro culture conditions.

Morphology, sex ratio and gene expression of day 14 in vivo and in vitro bovine embryos

The present study was designed to compare Day 14 bovine embryos that were produced entirely in vitro using the post-hatching development (PHD) system with in vivo-derived embryos without or with transient PHD culture from Day 7 to Day 14. Embryos on Day 14 were used for sex determination and gene expression analysis of PLAC8, KRT8, CD9, SLC2A1, SLC2A3, PGK1, HSF1, MNSOD, HSP70 and IFNT using real-time quantitative (q) polymerase chain reaction (PCR). First, Day 7 in vivo- and in vitro-produced embryos were subjected to the PHD system. A higher rate of survival was observed for in vitro embryos on Day 14. Comparing Day 14 embryos produced completely in vivo or completely in vitro revealed that the mean size of the former group was greater than that of the latter (10.29±1.83 vs 2.68±0.33mm, respectively). Expression of the HSP70 and SLC2A1 genes was down- and upregulated, respectively, in the in vitro embryos. The present study shows that in vitro embryos cultured in the PHD system are smaller than in vivo embryos and that of the 10 genes analysed, only two were differentially expressed between the two groups. These findings indicate that, owing to the poor survival rate, the PHD system is not reliable for evaluation of in vitro embryo quality.

Energy substrate influences the effect of the timing of the first embryonic cleavage on the development of in vitro-produced porcine embryos in a sex-related manner

In vitro culture conditions and certain events during the earliest stages of development are linked to embryonic survival, possibly in a sex-related manner. In vitro-produced (IVP) porcine embryos cultured with glucose (IVC-Glu) or pyruvate-lactate (IVC-PL) were tested for any relationship between the timing of the first embryonic cleavage and development and sex ratio. The embryos were assigned to IVC-Glu or IVC-PL groups and classified depending on the timing of their first cleavage: 24, 26, 30, and 48 hr post-insemination (hpi). They were cultured separately in vitro and evaluated for cleavage rate and pattern, blastocyst rate and stage, cell number, apoptosis, and sex ratio. Regardless of energy source, the percentage of two-cell stage and fragmented embryos at the time of their first cleavage was, respectively, higher and lower in early-cleaving embryos. Those embryos cleaved by 24 hpi developed to blastocysts at a higher rate (IVC-Glu: 37.90 ± 3.06%; IVC-PL: 38.73 ± 4.08%) than those cleaved between 30 and 48 hpi (IVC-Glu: 5.87 ± 3.02%; IVC-PL: 8.41 ± 3.50%). Furthermore, a shift toward males was seen among embryos first cleaved before 30 hpi, versus towards females among those cleaved later. The early-cleaving embryos, only from the IVC-PL group, had a higher proportion of expanded blastocysts (81.05 ± 6.54% vs. 13.33 ± 13.33%) with higher cell numbers than their late-cleaving counterparts. Moreover, a shift toward males only appeared at the blastocyst stage in IVC-PL embryos. These findings confirm that the timing of the first cleavage influences development of IVP porcine embryos in a sex-related manner, and it depends on the main energy source of the in vitro culture medium.

A novel approach to sexing bovine blastocysts using male-specific gene expression

When examining gene expression profiles for the purposes of assessing embryo quality, it is imperative that sex be considered, because many embryonic transcripts have sex-related expression patterns. The objective of this study was to systematically examine eight Y chromosome linked genes (DDX3Y, EIF1AY, HSFY, SRY, TSPY, USP9Y, ZFY, and ZRSR2Y) to characterize their expression in bovine blastocysts and to examine the usefulness of this expression for the purpose of RNA-based embryo sexing. In order to examine the expression of these genes, pools of blastocysts (groups of 10 and 20) as well as single embryos (N = 50) were analyzed with reverse transcriptase polymerase chain reaction (RT-PCR) and reverse transcriptase quantitative PCR (RT-qPCR). Of the 50 single embryos, 32 were concurrently sexed with DNA-based methods. Transcripts of DDX3Y, EIF1AY, TSPY, USP9Y, ZFY and ZRSR2Y were detected in the pooled and single blastocysts, but no transcripts were detected for HSFY or SRY. After performing DNA-based sexing experiments, we concluded that this expression was restricted to the male embryos. The consistency of the expression varied according to the gene as well as the specific primer set. Three genes were expressed in the full set of male embryos, DDX3Y, USP9Y, and ZRSR2Y and therefore represent good candidates for RNA-based sexing methods.

The influence of gamete co-incubation length on the in vitro fertility and sex ratio of bovine bulls with different penetration speed

The objectives of this work were to evaluate whether the sperm penetration speed is correlated to the in vitro fertility and whether adapting the gamete co-incubation length to the kinetics of the bull improves in vitro fertility and affects the sex ratio. In vitro matured oocytes were co-incubated with spermatozoa from four different bulls (A-D). At various post-insemination (p.i.) times (4, 8, 12, 16 and 20 h), samples of oocytes were fixed and stained with DAPI for nuclei examination, while the remaining ones were transferred into culture to evaluate embryo development. The blastocysts produced were sexed by PCR. Two bulls (A and B) had faster kinetics than the others (C and D), as shown by the higher penetration rates recorded at 4 h p.i. (43%, 30%, 11% and 6%, respectively for bulls A, B, C and D; p<0.01). The differences in the kinetics among bulls did not reflect their in vitro fertility. The incidence of polyspermy was higher for faster penetrating bulls (36%, 24%, 16% and 4%, respectively for bulls A, B, C and D; p<0.01) and at longer co-incubation times (0%, 16%, 19%, 30% and 34%, respectively at 4, 8, 12, 16 and 20 h p.i.; p<0.01). The fertilizing ability of individual bulls may be improved by adapting the co-incubation length to their penetration speed. A sperm-oocyte co-incubation length of 8 h ensured the greatest blastocyst yields for the two faster penetrating bulls. On the contrary, 16 h co-incubation was required to increase (p<0.01) cleavage rate of the two slower bulls. Bulls with a faster kinetics did not alter the embryo sex ratio towards males. The female/male (F/M) ratios recorded were 2.1, 1.4, 1.2, 1.3 and 1.6, respectively at 4, 8, 12, 16 and 20 h p.i.

Time exposure period of bovine oocytes to sperm in relation to embryo development rate and quality

The objective of the study was to determine the effect of different bovine gamete coincubation times on fertilization and embryo development performance. In vitro matured COCs were co-incubated with sperm at a concentration of 1.5 × 10⁶ spermatozoa/ml in TALP medium for 3 hours (T 3, n = 362), 6 hours (T 6, n = 358), or 18 hours (T 18, n = 350). At the end of the coincubation period COCs from times 3 and 6 groups were post-incubated in a new well of fertilization medium without sperm for additional 15 and 12 h, respectively. Cumulus Oocyte Complexes from the T 18 were co-incubated with the sperm suspension for 18 hours. Presumptive zygotes were cultured for 9 days and embryo development was evaluated on days 2, 8, and 9. Thirty blastocysts from each group were stained and total number of nuclei was recorded. The mean (± SEM) percentages of zygotes to develop into ≥2 cell stage were 71.9 ± 5.0; 72.5 ± 5.3 and 81.2 ± 6.1 % for T 3, 6, and 18, respectively, on day 2 and they did not differ (P = .3) among groups. The mean percentage of blastocysts developed on day 8 (25.6 ± 2.8; 24.2 ± 3.3; 28.4 ± 4.2 % for T 3, 6, and 18, resp.) did not differ (P = .4) among groups. The total number of embryonic nuclei was greater (P < .05) for the blastocysts produced from the shortest co-incubation time (T 3).

Influence of the semen deposition site on the calves' sex ratio in Simmental dairy cattle

It has been suggested that the time of insemination has effect on the calves' sex ratio because of the differences in timing of capacitation, motility and survival time of the X and Y spermatozoa in the female reproductive tract. We have conducted a field trial to study the effects of different semen deposition sites on the sex ratio and fertility in cattle. Two groups of 450 cows were inseminated via artificial insemination: group A was inseminated into the uterine body and group B was inseminated deep into the uterine horn ipsilateral to the ovary with dominant follicle. After applying several exclusion criteria, a total of 607 pregnant cows were considered for data analysis (group A = 318 and group B = 289 cows). The conception rate was 7% higher (p < 0.05) in the group A, with 23% more of the male calf pregnancies (p < 0.001). At the same time, 18% more of the female calves were calved in the group B (p < 0.005). The difference in male calves between the two groups was 21% and in female calves was 20% (p < 0.001). We conclude that semen deposition site plays a significant role in differences in gender ratio observed after calving. Intracornual semen deposition resulted in a higher ratio of female calves, whereas uterine body deposition site resulted in higher male calves ratio, probably contributing physiologically to the differences in motility, capacitation time, the lifespan of X vs Y spermatozoa and to the pronounced shift of X spermatozoa in the female genital tract.

The influence of sperm concentration, length of the gamete co-culture and the evolution of different sperm parameters on the in vitro fertilization of prepubertal goat oocytes

The aims of the present study were: (1) to evaluate the influence of sperm concentration (ranging from 0.5 × 106 to 4 × 106 spermatozoa/ml) and length of the gamete co-incubation time (2, 4, 6, 8, 10, 12, 16, 20, 24 or 28 h) on in vitro fertilization (IVF), assessing the sperm penetration rate; (2) to investigate the kinetics of different semen parameters as motility, viability and acrosome status during the co-culture period; and (3) to analyse the effect of the presence of cumulus–oocytes complexes (COCs) on these parameters. To achieve these objectives, several experiments were carried out using in vitro matured oocytes from prepubertal goats. The main findings of this work are that: (1) in our conditions, the optimum sperm concentration is 4 × 106 sperm/ml, as this sperm:oocyte ratio (approximately 28,000) allowed us to obtain the highest penetration rate, without increasing polyspermy incidence; (2) the highest percentage of viable acrosome-reacted spermatozoa is observed between 8–12 h of gamete co-culture, while the penetration rate is maximum at 12 h of co-incubation; and (3) the presence of COCs seems to favour the acrosome reaction of free spermatozoa on IVF medium, but not significantly. In conclusion, we suggest that a gamete co-incubation for 12–14 h, with a concentration of 4 × 106 sperm/ml, would be sufficient to obtain the highest rate of penetration, reducing the exposure of oocytes to high levels of reactive oxygen species produced by spermatozoa, especially when a high sperm concentration is used to increase the caprine IVF outcome.

Intrafollicular testosterone concentration and sex ratio in individually cultured bovine embryos

Recent studies have suggested a relationship between bovine follicular fluid testosterone concentration and the likelihood of the oocyte being fertilised by an X- or Y-bearing spermatozoon; however, this theory has been challenged. To further test this hypothesis, follicles were dissected from the ovaries of slaughtered heifers, measured and carefully ruptured. The cumulus–oocyte complex (COC) was removed and the follicular fluid collected and testosterone concentration determined by radioimmunoassay. COCs were matured, fertilised and cultured in an individually identifiable manner; all cleaved embryos (2- to 4-cell stage, n = 164) had their sex determined by PCR. Testosterone concentrations were positively skewed. There was no significant difference between follicular fluid testosterone concentrations in male and female embryos (mean ± s.e.m. 51.5 ± 5.59 and 49.5 ± 7.42 ng mL–1, respectively). Linear, quadratic and cubic logistical regression showed that follicular testosterone concentration could not reliably predict the sex of the embryo with odds ratios of 1.001, 1.013 and 1.066, repectively, and coefficient of determination (R2) values of 0.0003, 0.0126 and 0.0567, respectively. Follicular size and testosterone concentration were not related (R2 = 0.087). Finally, follicular size had no influence on embryo sex determination (P = 0.70). In conclusion, under the conditions of the present study, the likelihood of an oocyte being fertilised by an X- or Y-bearing spermatozoon was not affected by the size of the follicle from which it was derived, nor by the testosterone concentration in the follicular fluid.

Changes in testosterone or temperature during the in vitro oocyte culture do not alter the sex ratio of bovine embryos

High follicular testosterone levels have been associated with a skew in the sex ratio in favor of males following in vitro fertilization, whereas egg incubation temperature has been found to influence sex ratio in some reptiles. The incubation temperature interferes with the aromatase activity, resulting in a sex determination mechanism thought to be lost in mammals. In this work we aimed to test the effects of testosterone on sex ratio of bovine embryos produced in vitro and to determine whether effects of sex and temperature are effectively decoupled in mammals. Bovine oocytes were in vitro matured for 22 hr in TCM199, PVA, FSH and LH after a 22 hr meiotic arrest in TCM199, PVA and roscovitine 25 microM. Matured oocytes were in vitro fertilized and cultured up to Day 3, and embryos having three or more cells were sexed. In the first experiment, testosterone (0, 30, 300 and 1,500 nM), present both during meiotic inhibition and subsequent in vitro maturation (IVM), did not affect development rates or embryonic sex ratio. In the second experiment, increasing incubation temperatures (38, 39 or 40 degrees C) during meiotic inhibition and subsequent IVM, reduced embryo development, but did not change the sex ratio. Under our experimental conditions, testosterone does not promote a preferential selection of Y-chromosome bearing spermatozoa by the oocyte, and temperature and sex ratio seems to be decoupled in mammals.

Consequences of in vitro culture conditions on embryo development and quality

Despite major efforts directed at improving the yield of blastocysts from immature oocytes in vitro, the quality of such blastocysts continually lags behind that of blastocysts produced in vivo. These differences are manifested at the level of morphology, metabolism, gene expression and cryotolerance, and may have a knock-on effect further along the developmental axis. Evidence suggesting that in vitro culture conditions, while capable of producing blastocysts in relatively high numbers, are far from optimal with deficiencies being manifested in terms of abnormally large offspring. It is clear nowadays that modification of the post-fertilization culture environment in vitro can improve blastocyst quality to some extent.

Recovery, cryopreservation and fertilization potential of bovine spermatozoa obtained from epididymides stored at 5 degrees C by different periods of time

The objetive of the present study was to evaluate the effect of the interval between animal's death and sperm recovery on the freezability and fertilizing ability of spermatozoa from bull epididymides stored for different periods of time. Testis from 25 bulls were collected at the abattoir 2h after the slaughter. In the laboratory spermatozoa from one epididymis were recovered and analysed for motility. The remaining epididymis was stored for 24h (G24), 48h (G48) and 72h (G72) at 5 degrees C. At the end of each time period, spermatozoa were recuperated and cryopreserved in Tris-egg yolk and glycerol. Pre-freeze and post-thaw sperm samples were taken to assess total and progressive motility, concentration, membrane integrity and acrosome integrity. For evaluation of fertilizing ability, in each time period five straws of each bull were thawed, pooled and used for in vitro embryo production. The results showed that after 48h of storage there was a decline in total motility, which did not change until 72h. Progressive motility, plasma membrane and acrosome integrity were not affected by any of the storage periods. Conversely, all sperm parameters, except progressive motility, were reduced after cryopreservation. Embryo production was less (P<0.05) in the treatments than in the reference group. However, there was no differences (P>0.05) in blastoycst rate among experimental groups. Considering all the embryos produced by epididymal spermatozoa a greater proportion of female embryos was observed, which was similar to the reference embryos. The shift observed on sex ratio toward female for those two groups was also observed when they were compared with the expected 1:1 ratio (P<0.05). The results showed the possibility to produced in vitro embryos using cryopreseved spermatozoa from epididymides and stored for long period of time at 5 degrees C. These procedures became an important tool for animal preservation when the sperm cells cannot be cryopreserved immediately after the animal's death.

Post-biopsy bovine embryo viability and whole genome amplification in preimplantation genetic diagnosis

OBJECTIVE

To evaluate the effect of the biopsy of 8-cell to 16-cell bovine embryos on their subsequent development and the effect of whole genome amplification (WGA) on removed blastomeres.

DESIGN

Randomized study.

SETTING

Molecular genetics and animal reproduction laboratories.

PATIENT(S)

Cow ovaries obtained from slaughterhouses.

INTERVENTION(S)

The ovaries were punctured, and the oocytes were matured and fertilized in vitro. On the fourth day after fertilization, 8-cell to 16-cell bovine embryos were biopsied, one quarter of each embryo being removed. The blastomeres were submitted to WGA followed by polymerase chain reaction (PCR). The embryos were returned to culture for evaluation of their development.

MAIN OUTCOME MEASURE(S)

Subsequent rate of blastocyst development, embryo cell number, WGA efficiency, and sex determination.

RESULT(S)

A total of 92 embryos were submitted to biopsy. The blastocyst production was 53.3%, with 44.9% of hatching rate. These results were similar to those of the control group (66.0% and 42.6%) of 103 embryos. Overall, no impact was detected on embryo quality in blastocyst cell number between the two groups. Removed blastomeres were submitted to WGA, resulting in 98.2% of efficiency. However, only 59% of the samples were sexed by PCR.

CONCLUSION(S)

Biopsy of 8-cell to 16-cell bovine embryos did not affect their subsequent development. WGA was successful in removed blastomeres.

Consequences for the bovine embryo of being derived from a spermatozoon subjected to post-ejaculatory aging and heat shock: development to the blastocyst stage and sex ratio

The objective was to determine whether aging of sperm caused by incubation at normothermic (38.5 C) or heat shock (40 C) temperatures for 4 h prior to oocyte insemination affects sperm motility, fertilizing ability, competence of the resultant embryo to develop to the blastocyst stage and blastocyst sex ratio. In the first experiment, the percent of sperm that were motile was reduced by aging (P<0.001) and the reduction in motility was greater for sperm at 40 C compared to sperm at 38.5 C (P<0.01). In the second experiment, oocytes were inseminated with aged sperm. A smaller percent of oocytes fertilized with sperm aged at either temperature cleaved by Day 3 after insemination than oocytes fertilized with fresh sperm (P<0.05). There was no effect of sperm aging on the percent of oocytes or cleaved embryos that developed to the blastocyst stage. Aging of sperm before fertilization at 38.5 C reduced the percent of blastocysts that were male (P=0.08). In the third experiment, incubation of sperm at 38.5 C or 40 C for 4 h did not reduce fertilizing ability of sperm as determined by pronuclear formation at 18 h post insemination. In conclusion, aging of sperm reduced cleavage rate and the percent of blastocysts that were males but had no effect on the developmental capacity of the embryo. The effect of aging on cleavage rate may represent reduced motility and errors occurring after fertilization and pronuclear formation. Aging at a temperature characteristic of maternal hyperthermia had little additional effect except that polyspermy was reduced. Results indicate that embryo competence for development to the blastocyst stage is independent of sperm damage as a result of aging for 4 h at normothermic or hyperthermic temperatures.

Kinetics of fertilization and development, and sex ratio of bovine embryos produced using the semen of different bulls

The between bulls variation in in vitro fertility and the shift of sex ratio towards male embryos are two problems affecting the in vitro production (IVP) of bovine embryos. Our objective was to evaluate the kinetics of fertilization, embryo development and the sex ratio of the resulting embryos using the frozen/thawed semen of four different bulls. In a first experiment, the kinetics of pronucleus (PN) formation was evaluated at 8, 12 and 18 h post-insemination (hpi). Based upon the pronuclei sizes and the distance between the two pronuclei, inseminated oocytes were classified in three PN stages. Differences between bulls were observed at each time point, but were more important at 12 hpi. At 8 and 12 hpi bull III showed a significantly faster PN evolution by comparison with the three other bulls (P<0.05), while at 18 hpi, the proportion of the three PN stages was similar to those of bulls I and IV, bull II being delayed. In a second experiment, the kinetics of in vitro embryo development was compared using time-lapse cinematography. The analysis of embryos reaching the blastocyst stage revealed significant differences in the mean time of first cleavage (range of 22.7-25.6h, P<0.05), while the lengths of the subsequent three cell cycles did not differ between bulls. The early mean time of first cleavage with bull III was associated with an early blastulation and a high blastocyst rate at Day 7, in opposition to what was observed with bull II showing a later timing of first cleavage (first cleavage 22.1 hpi versus 25.5 hpi; blastulation 140.4 hpi versus 152.5 hpi; D7 blastocyst rates: 31.3% versus 21.9%; P<0.05). In a third experiment, 65-76 Day 8 blastocysts per bull were sexed by PCR. Only blastocysts obtained with bull III showed a shift in sex ratio towards male embryos (76% male embryos; P<0.05). Such shift was already observed at the 2-cell and morula stages. In conclusion, the bull influences the kinetics of PN formation, of embryo development and the sex ratio of the embryos. Moreover, those parameters might be related.

Influence of the duration of in vitro maturation and gamete co-incubation on the efficiency of in vitro embryo development in Italian Mediterranean buffalo (Bubalus bubalis)

The aim of this study was to investigate the effect of the duration of oocyte in vitro maturation (IVM) and gamete co-incubation on the in vitro embryo (IVEP) production efficiency in River buffalo. In Experiment 1, abattoir-derived cumulus oocyte complexes were fixed at 0, 3, 6, 9, 12, 15, 18, 21 and 24 h after the start of in vitro maturation to study the kinetics of nuclear maturation. In Experiment 2, cumulus oocyte complexes were fertilized in vitro following in vitro maturation for 18, 21, 24, 27 or 30 h. After 20 h of gamete co-incubation, presumptive zygotes were denuded and cultured in vitro in synthetic oviduct fluid (SOF) medium. In Experiment 3, following in vitro maturation and fertilization, presumptive zygotes were removed from fertilization drops at 8, 12, 16 and 20 h post-insemination (pi) and placed in culture as described above. Representative samples of oocytes were fixed at 4, 8, 12, 16 and 20 h to evaluate the sperm penetration rate and the incidence of polyspermy at different co-incubation times. The main conclusions of the study are that: (1) the majority of buffalo oocytes accomplish nuclear maturation between 21 and 24 h after the start of in vitro maturation; (2) both cleavage and blastocyst rates linearly decrease with increasing duration of in vitro maturation (from 18 to 30 h); (3) sperm-oocyte incubation for at least 16 h is required for maximum blastocyst yields.

Chromosome variation in the embryos of domestic animals

Chromosome abnormalities in the embryos of domestic animals are mostly eliminated during development. De novo chromosome abnormalities in the embryos of domestic animals have been detected in a larger proportion of embryos produced by in vitro fertilization and somatic cell nuclear transfer than in those produced by natural mating or artificial insemination. The increased incidence of abnormalities in embryos produced in vitro provides evidence for an influence of the embryo production procedures on chromosome stability. Research strategies involving cytogenetics, molecular biology and reproductive biotechnologies hold the promise of yielding insight into the mechanisms underlying chromosome instability in embryos and the impact of the in vitro environment on the chromosome make-up of embryos.

Progesterone and 17beta-estradiol, but not follicle stimulating hormone, alter the sex ratio of murine embryos fertilized in vitro

The objective was to determine the effects of adding progesterone, 17beta-estradiol (17beta-E2), and FSH during in vitro fertilization on development and sex ratio of murine embryos. Progesterone (33-330 pg/mL), 17beta-estradiol (17beta-E2); 10-70 pg/mL), and FSH (0.01-0.05 IU/mL), were added to human tubal fluid (HTF); this medium (with or without hormones) was used to pre-incubate sperm (2h) and to co-incubate sperm and oocytes (6h). Thereafter, the ova were washed and incubated in mM16 medium and embryo sex was determined (by PCR) on Day 4 (insemination=Day 0). There was no effect (P>0.05) of hormone treatments on rates of cleavage (6 h after cessation of co-incubation with sperm). The only significant effects of added hormones on development were a decrease in the rate of development to at least the morula stage in 165 pg/mL progesterone (0.46+/-0.03 vs. 0.54+/-0.05 in the control, mean+/-S.D.; P<0.05) and a decrease in the blastocyst rate in 0.03 IU/mL FSH (0.34+/-0.00 vs. 0.42+/-0.04 in the control, P<0.05). However, the ratio of male to female embryos was 1.61 and 2.90 following the addition of 99 pg/mL progesterone and 70 pg/mL 17beta-E2, respectively; both of these ratios were different (P<0.01) than in the control group (1.20). In contrast, the addition of FSH to the medium had no significant effect on this ratio (range, 0.78-1.02). We concluded that the addition of progesterone and estradiol to the media during in vitro fertilization did not enhance embryonic development, but significantly increased the proportion of male murine embryos.

Effect of duration of oocyte maturation on the kinetics of cleavage, embryo yield and sex ratio in cattle

The aim of the present study was to examine the effect of maturation for 16 v. 24 h on the kinetics of development and the sex ratio of bovine embryos. Oocytes were inseminated at 16 or 24 h after the beginning of maturation using frozen–thawed bull semen. Two-cell embryos at 24, 28, 32, 36, 40, 44 and 48 h post-insemination (hpi) and blastocysts at Days 6, 7 and 8 from both groups were snap-frozen individually and stored at –80°C until determination of embryo sex. Insemination at 16 h resulted in a lower cleavage rate at 48 hpi than insemination at 24 h (70.6% v. 77.1%, respectively, P < 0.05). In terms of the evolution of cleavage divisions, insemination at 24 h resulted in a typical pattern of cleavage such that by 32 hpi, ~58% of presumptive zygotes had cleaved. In contrast, first cleavage following insemination at 16 h was significantly slower such that by 32 hpi, ~35% of presumptive zygotes had cleaved. Duration of IVM did not affect blastocyst yield (~37%). The overall sex ratio of 2-cell embryos at 48 hpi differed from 1 : 1 in favour of males in both groups (24 h: 55.9 v. 44.1%; 16 h: 59.1 v. 40.9%, P < 0.05). Similarly, the overall sex ratio of blastocysts differed from 1 : 1 in both groups (24 h: 59.7 v. 40.3%; 16 h: 58.5 v. 41.5%, P < 0.05). In conclusion, timing of gamete interaction and maturity of the oocyte at the time of the interaction can affect the kinetics of the early cleavage divisions but has no effect on the sex ratio of the embryos produce.

A role for cell sex in stem cell-mediated skeletal muscle regeneration: female cells have higher muscle regeneration efficiency

We have shown that muscle-derived stem cells (MDSCs) transplanted into dystrophic (mdx) mice efficiently regenerate skeletal muscle. However, MDSC populations exhibit heterogeneity in marker profiles and variability in regeneration abilities. We show here that cell sex is a variable that considerably influences MDSCs' regeneration abilities. We found that the female MDSCs (F-MDSCs) regenerated skeletal muscle more efficiently. Despite using additional isolation techniques and cell cloning, we could not obtain a male subfraction with a regeneration capacity similar to that of their female counterparts. Rather than being directly hormonal or caused by host immune response, this difference in MDSCs' regeneration potential may arise from innate sex-related differences in the cells' stress responses. In comparison with F-MDSCs, male MDSCs have increased differentiation after exposure to oxidative stress induced by hydrogen peroxide, which may lead to in vivo donor cell depletion, and a proliferative advantage for F-MDSCs that eventually increases muscle regeneration. These findings should persuade researchers to report cell sex, which is a largely unexplored variable, and consider the implications of relying on cells of one sex.

Effects of modification of in vitro fertilization techniques on the sex ratio of the resultant bovine embryos

The duration of sperm-oocyte co-incubation has been observed to affect the sex ratio of in vitro produced bovine embryos. The purpose of this study was to investigate some factors that may be responsible for the skewed sex ratio. The factors studied were selected combinations of the duration of co-incubation, the presence or absence of cumulus cells, and the level of hyaluronic acid (HA) in the culture medium. Experiment 1 examined the effect of selected combinations of different factors during the fertilization phase of in vitro oocyte culture. The factors were the nature of the sperm or its treatment, the duration of the sperm-oocyte co-incubation, and the level of hyaluronic acid in the culture medium. In experiment 2, the capacitation of frozen-thawed-Percoll-washed sperm (control), pre-incubated, and non-binding sperm was evaluated by the zona pellucida (ZP) binding assay and the hypo-osmotic swelling test (HOST). The purpose of experiment 3 was to determine the oocyte cleavage rate and sex ratio of the embryos (>5 cells) produced as a consequence of the 10 treatments used in experiment 1. In treatments 1-3 (experiments 1 and 3) COC were co-cultured with sperm for 1, 5 or 18 h. Polyspermic fertilization rose as the co-incubation period increased (1 h 6.5%, 5 h 15.9%, 18 h 41.8%; P<0.05), and the highest rate of normal fertilization was observed for 5h culture (73.4%; P<0.05). The sex ratio was significantly (P<0.05) skewed from the expected 50:50 towards males following 1 h (64.4%) and 5 h (67.3%) co-incubation, but was not affected by 18 h incubation (52.3%). In treatment 4, sperm was pre-incubated for 1h and cultured with COC for 5 h. Relative to control sperm, pre-incubation of sperm increased ZP binding (116 versus 180 per ZP; P<0.05) and decreased the proportion of HOST positive sperm (65.8-48.6%; P<0.05; experiment 2). Pre-incubation did not affect the rates of polyspermy, normal fertilization or the sex ratio of the embryos (experiments 1 and 3). The oocytes used in treatments 5-10 of experiments 1 and 3 were denuded prior to fertilization. Co-incubation of denuded oocytes for 1h (treatment 5) or 5h (treatment 6) resulted in levels of polyspermic fertilization similar to that for treatment 2 with significantly lower levels of normal fertilization (41.7% and 52.6%, respectively; P<0.05), and the 1h co-incubation significantly skewed (P<0.05) the proportion of male embryos to 70.0%. Denuded oocytes were fertilized for 5h with sperm unable to bind to cumulus cells (NB sperm) in treatment 7 or those that bound to cumulus cells (B) in treatment 8. These two treatments had similar rates of polyspermic, normal and non-fertilization. However, the B sperm caused the sex ratio of the embryos to be significantly skewed to males (63.9%; P<0.05). Fertilization of denuded oocytes in medium containing hyaluronic acid (0.1 mg/ml, treatment 9; 1.0 mg/ml treatment 10) significantly (P<0.05) reduced the incidence of polyspermic fertilization relative to treatments 2 and 6, and normal fertilization relative to treatment 2, but did not affect the sex ratio of the embryos. It was concluded that exposure of sperm to cumulus cells, either before fertilization of denuded oocytes or during the process of fertilization of complete COC, increased the proportion of male embryos produced by in vitro culture. It was hypothesized that this may be due to the capacitation state of the sperm, the cumulus-sperm interaction, and/or the ability of the sperm to bind to cumulus cells or oocytes.

Integrated morphophysiological assessment of two methods for sperm selection in bovine embryo production in vitro

Extensive work was done regarding the ability of Swim up and Percoll gradient to select functional sperm for in vitro embryo production (IVP) systems. The aim of this work was to compare Swim up and Percoll as methods of sperm selection by ultrastructural, biochemical and functional studies. Frozen-thawed semen from two bulls (Experiments 1 and 2, respectively) were treated using Swim up or Percoll discontinuous gradients. Motility, sperm membrane ultrastructure, sperm proteins, in vitro embryo production (insemination doses, cleavage, embryo yield and quality) and embryo sex ratio were scored and compared. Electron transmission microscopy of outer sperm membranes showed higher (P<0.05) percentage of sperm with lost acrosomes in Percoll treated samples compared to Swim up. A differential protein pattern was also detected. When in vitro embryo production was performed, Percoll gradient produced higher (P<0.05) number of fertilizing doses (7.6 versus 5.9, Bull 1; 13.5 versus 7.8, Bull 2) and higher sperm motility (90% versus 76.6%, Bull 1; 81.7% versus 68.3%, Bull 2) than Swim up. The percentage of cleavage (Day 3) was similar in both treatment groups, whereas embryo production rate (Day 7) was higher (39.4% versus 30.2%, Bull 1; 38% versus 32.4%, Bull 2; P<0.05) when Percoll gradient was used. The percentage of hatched embryos (Day 11) and sex ratio did not differ. Total cell counting and embryo differential staining (inner cell mass and trophoblast cells) of Day 7 embryos showed that Percoll treated sperm produced better quality embryos compared to Swim up. We concluded that Percoll had a better performance selecting sperm and an enhanced capacity for embryo production when compared with the Swim up procedure; this could be attributed to a better acrosome exocytosis, associated to the absence of certain membrane proteins.

Effect of Maturation Culture Period of Oocytes on the Sex Ratio of In Vitro Fertilized Bovine Embryos

It has been suggested that the maturational stage of oocytes at time of insemination influences the sex ratio of resulting embryos. However, there are very few reports concerning the relationship between the maturation culture period of oocytes and the sex ratio of resulting embryos. The objective of this study was to investigate the effects of in vitro maturation culture period for bovine oocytes on the sex ratio of in vitro produced blastocysts using a novel technique of loop-mediated isothermal amplification (LAMP). Cumulus-oocyte complexes were collected from the ovaries of slaughtered cows, and then matured in vitro for various periods (16, 22, 28, and 34 h). After maturation culture for each period, the oocytes were inseminated with frozen-thawed spermatozoa, and then cultured in vitro. Blastocysts were harvested on Day 7 after insemination, and the sex of the embryos was examined using the LAMP method. The rates of oocytes matured to the metaphase II stage were significantly lower (P < 0.05) in the 16-h maturation group than in the other groups. The proportion of blastocyst formation after insemination was significantly higher (P < 0.05) in the 22-h maturation group than in the other groups. The proportion of male blastocysts increased with the increase in maturation culture period. The proportion of male blastocysts derived from oocytes matured for 34 h was significantly higher (P < 0.05) than from oocytes matured for 16 and 22 h. These results indicate that the sex ratio of in vitro fertilized embryos is apparently influenced by the maturation culture period of the oocytes.

The effect of gamete co-incubation time during in vitro fertilization with frozen-thawed unsorted and sex-sorted ram spermatozoa on the development of in vitro matured adult and prepubertal ewe oocytes

In vitro matured adult (Experiment 1) and prepubertal (Experiment 2) ewe oocytes were co-incubated with unsorted or sex-sorted frozen-thawed spermatozoa for 2 to 3 h (short) or 18 to 20 h (long) to determine the effects of reducing the gamete co-incubation time during IVF on subsequent embryonic development in vitro. For oocytes derived from adult ewes, there were no differences in oocyte fertilization and cleavage at 24 h post insemination (hpi) between types of spermatozoa or co-incubation times (P > 0.05). By 48 hpi, oocyte cleavage was higher after a short (390/602, 64.8%) compared with a long (381/617, 61.7%) co-incubation (P < 0.05), and was not significantly different for unsorted (266/372, 71.5%) and sex-sorted (505/849, 59.9%) spermatozoa. Blastocyst formation from cleaved oocytes was similar for unsorted (150/266, 56.4%) and sex-sorted (295/505, 58.4%) spermatozoa, but was higher after a short (240/390, 61.5%) than long (205/381, 53.8%) co-incubation (P < 0.05). Oocyte development to the blastocyst stage was not different for unsorted (150/372; 40.3%) and sex-sorted (295/847; 34.8%) spermatozoa but was significantly increased by a short (240/602, 39.9%) compared with a long (205/617, 33.2%) co-incubation. Fertilization of oocytes from prepubertal ewes was similar for types of spermatozoa and for duration of co-incubation. Oocyte cleavage (48 hpi) was similar for a short (241/377, 63.9%) and long (226/349, 64.8%) co-incubation with unsorted spermatozoa, but was increased (P < 0.05) by a long co-incubation (286/500, 57.2% versus 163/517, 31.5%) with sex-sorted spermatozoa. Blastocyst formation from cleaved oocytes was similar for unsorted (230/467, 49.3%) and sex-sorted (186/449, 41.4%) spermatozoa, and a short (200/404, 49.5%) or long (216/512, 42.1%) co-incubation. However, oocyte development to the blastocyst stage was higher (P < 0.05) after IVF with unsorted (230/726, 37.1%) than sex-sorted (186/1017, 18.3%) spermatozoa. Reducing the duration of gamete co-incubation did not deleteriously affect the in vitro development of adult and prepubertal ewe derived oocytes after IVF with unsorted and sex-sorted spermatozoa. In general, sex-sorting had no substantial influence on fertilization and embryo development rates.

Relationship between oxygen consumption and sex of bovine in vitro fertilized embryos

The present study was conducted to examine the relationship between the oxygen consumption rate and sex ratio of bovine in vitro fertilized embryos on each day of blastocyst formation. The quality of blastocysts collected on day 7, 8, and 9 after in vitro fertilization (IVF) were categorized as ranks A and B (excellent and good, respectively) based on microscopic observation of the morphology. The oxygen consumption rate and sex of individual blastocysts were evaluated using two novel techniques: scanning electrochemical microscopy (SECM) and loop-mediated isothermal amplification (LAMP), respectively. The oxygen consumption rates of embryos of rank A were significantly higher (p < 0.05) than those of rank B, irrespective of the day of blastocyst appearance after IVF. Neither did the proportion of male embryos of ranks A and B differ significantly from each other at any of the days examined, nor from the average proportion (53%). The oxygen consumption rate of embryos of rank B collected on day 8 was significantly higher (p < 0.05) in female embryos than in male embryos collected on the same day. However, there were no apparent differences of oxygen consumption rates at each day of blastocyst appearance between male and female embryos of rank A. These results indicate that the oxygen consumption rate of individual embryos reflects their quality but does not correlate with the sex ratio of embryos of excellent quality.

The epigenetic environment: secondary sex ratio depends on differential survival in embryogenesis

Live human births are usually more than half male, in spite of excess losses of males throughout fetal development. These observations together demand an excess of males near the beginning of pregnancy greater than that seen at birth. Reductions of the usual excess of males among human live births have widely been considered to represent consequences of untoward circumstances surrounding conception. Repeated competent research efforts have found no evidence for any bias in gametogenesis or fertilization in favour of Y-bearing sperm. Male embryogenesis is faster and more efficient, leaving females in excess among failures before the fetal period. Sex differences in speed and efficiency of embryogenesis, dependent for example on epigenetic differences such as genomic imprinting, produce an excess of males at the transition from embryogenesis to clinical pregnancy, that will survive the male excess of losses throughout the fetal period, to yield an excess of males among live births. Changes in, or mediated by, the epigenetic environment of embryogenesis provide the most plausible prospects for causes of changes in secondary sex ratio.

Post Hatching Development: a Novel System for Extended in Vitro Culture of Bovine Embryos

Although acceptable rates of blastocyst formation are achieved with in vitro production of bovine embryos, several problems still compromise the subsequent development of the fetus and newborn, especially in embryos originating from somatic cell nuclear transfer. Routinely, the potential development of a bovine conceptus is predicted either on blastocyst quality or on various parameters related to the embryonic-fetal development in a foster mother. These methods are either imprecise or costly, highlighting the need for more reliable and practical methods to evaluate early embryonic development and differentiation. Thus, our aim was to improve the in vitro culture of embryos post hatching and to define a stable and repeatable system to monitor the development of bovine embryos. For that, in vitro-derived embryos were cultured in agarose gel tunnels in a modified culture medium (SOFaaci within 10% fetal bovine serum and 27.7 mM glucose). Daily monitoring of embryo length revealed that 56%-67% of the embryos in culture showed rapid growth and elongated until Day 13. Electron microscopy of elongated embryos at Day 14 confirmed successful localization of differentiated cells forming the trophoblast and hypoblast, with the definition of the Rauber layer. In conclusion, a stable culture system of post hatching embryos was first defined and can be used as a model for rapid growth, elongation, and initial differentiation of bovine post hatching embryos produced entirely in vitro.