Developmental, qualitative, and ultrastructural differences between ovine and bovine embryos produced in vivo or in vitro

Alterations in ultrastructural morphology of two-cell bovine embryos produced in vitro and in vivo following a physiologically relevant heat shock

Exposure of cultured preimplantation embryos to temperatures similar to those experienced by heat-stressed cows inhibits subsequent development. In this study, the effects of heat shock on the ultrastructure of two-cell bovine embryos were examined to determine mechanisms for inhibition of development. Two-cell embryos produced in vitro were harvested at approximately 28 h postinsemination and cultured for 6 h at one of three temperatures: 38.5 degrees C (cow body temperature), 41.0 degrees C (characteristic temperature for heat-stressed cows), or 43.0 degrees C (severe heat shock). Ultrastructural examinations revealed that both heat shocks resulted in the movement of organelles towards the center of the blastomere. In addition, heat shock increased the percentage of mitochondria exhibiting a swollen morphology. Distance between the membranes comprising the nuclear envelope was increased but only when embryos were treated at 43.0 degrees C. To determine whether ultrastructural responses to heat shock in culture were similar for embryos produced in vitro and in vivo, two-cell embryos were collected from superovulated Angus cows 48 h postinsemination and treated ex vivo for 6 h at 38.5 degrees C or 41.0 degrees C. Again, heat shock caused an increase in number of swollen mitochondria and movement of organelles away from the periphery of the blastomere. Exposure of two-cell bovine embryos to physiologically relevant elevated temperatures causes disruption in ultrastructural morphology that is inimical to development. The observation that overall morphology and response to heat was similar for embryos produced in vitro and in vivo implies that the former can be a good model for understanding embryonic responses to heat shock.

Oocyte and embryo quality: effect of origin, culture conditions and gene expression patterns

In general, the majority of immature bovine oocytes fail to develop to the blastocyst stage following maturation, fertilization and culture in vitro. The evidence suggests that while culture conditions during in vitro embryo production can impact on the developmental potential of the early embryo, the intrinsic quality of the oocyte is the key factor determining the proportion of oocytes developing to the blastocyst stage. In addition, evidence suggests that the period of post-fertilization embryo culture is the most critical in determining blastocyst quality. This paper reviews the current literature, with emphasis on the bovine model, demonstrating evidence for an effect of oocyte origin and/or in vitro maturation conditions on the developmental capacity and gene expression patterns in the oocyte. Furthermore, the well-documented effects of post-fertilization culture environment on embryo gene expression and quality are highlighted.

Resumption of metabolic activity of vitrified/warmed ovine embryos

To evaluate resumption of metabolic activity of vitrified ovine embryos during a short time immediately after warming, blastocysts collected from superovulated Sarda ewes were incubated with (35)S-methionine. In vitrified/warmed embryo groups the protein secretion significantly (P < 0.05) increased from 0 to 24 hr of culture, reaching significantly (P < 0.01) higher activity at 18-24 hr and dropping to values similar to the control nonvitrified embryo group at 29-35 hr. Within the control group at 29-35 hr there was a significantly (P < 0.01) higher level of protein secretion compared to the other interval times. The electrophoretic pattern showed a 48-50 kDa secreted protein identified as urokinase-type plasminogen activator (PA). The caseinolytic assay of PA activity showed a course similar to protein secretion in both vitrified and control groups. During 29-35 hr of culture, we did not observe any improvement in PA activity as seen for secreted proteins. At this time, we observed the secretion of a new 20 kDa protein that was not present in vitrified/warmed embryos. Analysis of BrDU incorporation in newly synthesised DNA showed a significant (P < 0.01) improvement in positive cell number from 3 to 9 hr after warming, reaching a value similar to that of the control group at 12 hr of culture. Our results suggest that vitrified/warmed embryos require 9-12 hr of culture to complete resumption of DNA synthesis and 29-35 hr to re-acquire the full capacity of protein secretion but not the qualitative secretion pattern.

Current status of embryo technologies in sheep and goat

This review presents an overview of the technical bases of in vivo and in vitro embryo production in sheep and goat. The current limitations of in vivo production, such as variability of response to the hormonal treatment, fertilization failure in females showing a high ovulatory response, and the importance of premature regressed CL in the goat, are described along with possibilities for improvement. The new prospects offered by in vitro embryo production, by repeated ovum pick-up from live females and by juvenile breeding, are presented along with their limiting steps and research priorities. The recent improvements of embryo production and freezing technologies could be used for constitution of flocks without risks of disease transmission and will allow wider propagation of valuable genes in small ruminants populations in the future.

Assessment of mammalian embryo quality: what can we learn from embryo morphology?

Embryo morphology assessment, however imperfect it may be, is at present the most popular method for embryo selection prior to transfer, both in human and bovine assisted reproduction. A major difference between human and bovine embryos is the fact that in the latter, assessment of morphology is jeopardized by the opacity of the blastomeres, which is caused by lipid droplet accumulation. This opacity makes it difficult to assess nuclear and nucleolar morphology, aspects which can easily be evaluated in human zygotes or early cleaving embryos. However, recent research which focused on correlation between bovine embryo morphology and embryonic ultrastructure, gene expression and cryoresistance, has provided evidence that much more can be deduced from mere embryo morphology than previously thought. Morphological features such as colour of the blastomeres, the extent of compaction, timing of blastocyst formation and expansion and diameter of the embryo at hatching can be linked with embryo quality. On the other hand, cattle embryos of deviant chromosomal constitution or with aberrant genetic make-up cannot be selected against by means of the current morphological techniques. Possible solutions include the visualization of bovine pronuclei at the zygote stage by means of ultracentrifugation or multiphoton laser scanning microscopy, and adjustment of genetic analysis in order to reconstruct embryo genetic make-up starting from the biopsy material.

Effect of ovariectomy and graft position on cryopreserved common wombat (Vombatus ursinus) ovarian tissue following xenografting to nude mice

Ovarian tissue xenografting may be applied to increase the population size of rare or endangered animals. However, optimal grafting conditions, such as graft position and recipient hormonal status, are yet to be established. The present study, using common wombat ovarian tissue, showed that development of xenografted ovarian tissue to the antral follicle stage can be achieved irrespective of graft position. However, increased graft recovery rates and follicle survival were evident after grafting under the kidney capsule compared with grafting to subcutaneous sites. No increase in follicle development was observed after placing grafts both under the kidney capsule and subcutaneously in the one recipient compared with grafts placed under the kidney capsule alone or subcutaneously alone. Removal of the recipient’s own ovaries at the time of grafting accelerated graft follicle development, with antral follicles seen by Week 12 after grafting compared with by Week 16 in recipients that retained their own ovaries. More oocytes were collected from xenograft recipients receiving hormonal stimulation before collection compared with non-stimulated recipients. No oocytes were mature (extruded a polar body) at the time of collection or after a subsequent period of in vitro maturation. This is the first study to demonstrate that antral follicle development can occur and oocytes can be collected from xenografted common wombat ovarian tissue.

Defined media for vitrification, warming, and rehydration: effects on post-thaw protein synthesis and viability of in vitro derived ovine embryos

The purpose of this study was to assess the viability (rates of re-expanding and hatching in vitro), of in vitro derived ovine blastocysts using vitrification and warming/rehydration media containing fetal calf serum (20% FCS) or polyvinyl alcohol (0.1% PVA), and the incorporation of labelled methionine in protein synthesised during the first 4h after cryopreservation. In experiment 1, after 60 h culture in TCM-199 supplemented with 10% FCS, the hatching rates of blastocysts that had been vitrified, warmed, and rehydrated in media containing only PVA (p/p) were significantly (P<0.05) lower than those vitrified in medium containing PVA with warming and rehydration in medium containing FCS (p/s). Blastocysts that were vitrified in medium containing FCS and warmed and rehydrated in medium with PVA (s/p) had hatching rates that were significantly lower (P<0.01) than those vitrified, warmed, and rehydrated in media with only FCS (s/s). After warming, the number of dead cells in the p/p group was significantly (P<0.05) lower than in all other groups. In experiment 2, the [35S]methionine uptake by embryonic cells of the s/p group was significantly (P<0.01) higher than in other groups. The incorporation of labelled methionine into newly synthesised proteins was significantly lower in the p/p group (P<0.01) than in all other groups. No differences in the newly synthesised proteins were observed between groups. In conclusion, these results suggest that it is possible to replace serum with defined macromolecules in vitrification and warming/rehydration media for in vitro derived ovine blastocysts but this leads to a decrease in viability and a reduction in protein synthesis after warming.

Embryo survival and recipient pregnancy rates after transfer of fresh or vitrified, in vivo or in vitro produced ovine blastocysts

The aim of this study was to assess the effect of production system and of cryopreservation of ovine embryos on their viability when transferred to recipients. The experimental design was an unbalanced 2 x 2 factorial design of two embryo production systems (in vivo versus in vitro) and two embryo preservation conditions prior to transfer (transferred fresh versus transferred after vitrification/warming). For the production of blastocysts in vivo, crossbred donor ewes (n=30) were synchronised using a 13-day intravaginal progestagen pessary. Ewes received 1500 IU equine chorionic gonadotropin (eCG) 2 days before pessary withdrawal, and were mated 2 days after pessary withdrawal and embryos were recovered surgically (6 days after mating). Blastocysts were produced in vitro (IVP) using standard techniques. Recipients (n=95) were synchronised using a progestagen pessary and received 500 IU eCG at pessary removal and were randomly assigned to receive (two per recipient) in vivo fresh (n=10), in vivo vitrified (n=10), in vitro fresh (n=35) or in vitro vitrified (n=40) blastocysts. Recipients were slaughtered at day 42 of gestation and foetuses recovered. Pregnancy and embryo survival rates were recorded and analysed using CATMOD procedures. Foetal weights and crown-rump lengths were recorded and analysed using generalised linear model (GLM) procedures. There were no statistically significant interactions between the effects of embryo production system and preservation status at transfer on pregnancy rate and embryo survival. The pregnancy rate following transfer of fresh IVP blastocysts was lower (P<0.07) than that of in vivo embryos (54.3% versus 90.0%, respectively). Vitrification resulted in a decrease in pregnancy rate, the effect being more pronounced in the case of IVP embryos (54.3-5.0%, P<0.001) compared with in vivo embryos (90.0-50.0%), although the absolute change was similar (49.3% versus 40.0%). Transfer of fresh IVP blastocysts resulted in a higher proportion of single (78.9% versus 33.3%) and lower proportion of twin (21.1% versus 66.7%) pregnancies than those produced in vivo. This was reflected in a significant difference in embryo survival rate (fresh: 32.8% versus 75.0%, P<0.01; vitrified: 2.5% versus 35.0%, P<0.001, for IVP and in vivo blastocysts, respectively). Similarly, all pregnancies resulting from the transfer of vitrified/warmed IVP blastocysts were single pregnancies, while 40% of those from vitrified/warmed in vivo blastocysts were twin pregnancies; this was reflected in an embryo survival rate of 35.0% versus 75.0%, respectively. There was a significant effect (P=0.0184) of litter size on foetal weight but not on foetal length (P=0.3304). Foetuses derived from the fresh transfer of IVP blastocysts were heavier (6.4+/-0.2g versus 5.8+/-0.2g, respectively, P<0.05) and longer (5.2+/-0.1cm versus 4.8+/-0.1cm, respectively, P<0.01) than those derived from fresh in vivo blastocysts. There was no difference in these parameters as a consequence of vitrification of IVP embryos. However, in vivo blastocysts subjected to vitrification resulted in heavier (6.6+/-0.3g versus 5.8+/-0.2g, respectively, P=0.055) and longer (5.2+/-0.1cm versus 4.8+/-0.1cm, respectively, P<0.05) foetuses than their counterparts transferred fresh.