Cytogenetic analysis of ethanol-induced parthenogenesis

Transgenic cloned mice expressing enhanced green fluorescent protein generated by activation stimuli combined with 6-dimethylaminopurine

Most studies of mouse cloning successfully achieved activation of the reconstructed oocytes by strontium (Sr) combined with cytochalasin B (CB) treatment. A protein kinase inhibitor, 6-dimethylaminopurine (6-DMAP), was used to inhibit the activity of maturation promoting factor for activation of oocytes, but it has never been successfully applied in mouse cloning. This study investigates the activation efficiency of 6-DMAP in mouse somatic cell nuclear transfer (SCNT). Higher parthenogenetic blastocyst rates (71-72%, p < 0.05) were achieved in the oocytes treated with Sr6D (10 mM Sr combined with 2 mM 6-DMAP for 4 h) and Sr6D + SrCB (Sr6D for 2 h then Sr combined with 5 mug/ml CB for another 2 h), and a higher rate of hatching and hatched blastocyst was observed in the Sr6D + SrCB group (31%, p < 0.01) compared with other treatment groups (1-8%). For mouse cloning, cumulus cells of enhanced green fluorescent protein (EGFP)-expressed ESC chimera F1 were used as donor nuclei. Following activation, better development of the cloned embryos was observed in Sr6D + SrCB treatment. Moreover, different media, i.e. KSOM-AA, MEM-alpha and MK, for culturing cloned embryos were also compared in this study. Better morula/blastocyst (40%) and blastocyst (29%) rates were achieved in the embryos cultured in MEM-alpha medium (p < 0.05). Consequently, four EGFP cloned mice were generated in the activation treatment containing 6-DMAP following embryo transfer. In conclusion, treatment with 6-DMAP in combination with other activation stimuli successfully activates mouse reconstructed oocytes and support full-term development of the transgenic SCNT cloned embryos.

The employment of strontium to activate mouse oocytes: effects on spermatid-injection outcome

The present research investigated the effects of various strontium concentrations, in combination with different incubation periods, on mouse parthenogentic oocyte activation and blastocyst development. The results for blastocyst development showed a trend indicating that 10 mM strontium for 3 h was the optimal strontium protocol. Ethanol, an agent that incites oocyte activation via a monotonic rise in calcium, was employed as a control. The outcome of blastocyst formation arising from parthenogenic ethanol activation was significantly less (P< 0.001) than that achieved by the optimal strontium protocol. To assess the impact of strontium oocyte activation on embryo viability following fertilization with immature germ cells, the protocol of 10 mM strontium for 3 h was applied to oocytes injected with round spermatids and then compared with other protocols. The results indicate that following round-spermatid injection the benefits derived from strontium artificial oocyte activation are evident during both pre- and post-implantation development. However, in order to adjust the protocol to the most effective round-spermatid injection in relation to the oocyte cell cycle, injection was done 1.5 h after strontium activation followed by another 1.5 h activation in strontium. The implementation of round-spermatid injection in combination with this oocyte-activation protocol led to live-birth outcomes not significantly different to those outcomes obtained by mature spermatozoa.

Long-term alcohol exposure prior to conception results in lower fetal body weights

BACKGROUND

It is well known that alcohol consumption during pregnancy can result in lower birth weight babies but many women stop consuming alcohol prior to conception as a part of pregnancy planning. The purpose of this study was to determine whether alcohol consumption prior to conception may also have an effect on fetal development.

METHODS

Male and female C57BL/6J mice at 4, 6, or 8 weeks of age received either a single administration of alcohol (3.0 g/kg) via intragastric gavage (IG) each day for at least 60 days, or an isovolumetric IG administration of sterile water. After 60 treatment days, males and females within each age and treatment group were mated overnight. Females continued to receive daily alcohol treatments until conception. Males continued to receive treatments until all females were successfully mated. At conception, females were isolated and left undisturbed. On embryonic day 14, fetus number, size, and weight was determined.

RESULTS

Maternal food consumption, body weight at conception, and delay to conception onset did not differ between the two treatment groups or among the three age groups. Fetal body weights did not differ among the three age groups. Fetuses from females treated with alcohol had lower body weights compared to those treated with water. Male treatments did not seem to affect fetal body weight.

CONCLUSIONS

Fetal growth and development can be affected by alcohol consumption prior to the time of conception. Alcohol consumption prior to conception is a potential risk factor to fetal outcome and an important consideration for those females planning to have children.

Activation and early parthenogenesis of bovine oocytes treated with ethanol and strontium

Efficient artificial activation is indispensable for the success of cloning programs. Strontium has been shown to effectively activate mouse oocytes for nuclear transfer procedures, however, there is limited information on its use for bovine oocytes. The present study had as objectives: (1). to assess the ability of strontium to induce activation and parthenogenetic development in bovine oocytes of different maturational ages in comparison with ethanol; and (2). to verify whether the combination of both treatments improves activation and parthenogenetic development rates. Bovine oocytes were in vitro matured for 24, 26, 28, and 30 h, and treated with ethanol (E, 7% for 5 min) or strontium chloride (S, 10mM SrCl(2) for 5h) alone or in combination: ethanol+strontium (ES) and strontium+ethanol (SE). Activated oocytes were cultured in vitro in synthetic oviductal fluid (SOF) medium and assessed for pronuclear formation (15-16 h), cleavage (46-48 h) and development to the blastocyst stage (D7). Treatment with ethanol and strontium promoted similar results regarding pronuclear formation (E, 20-66.7%; S, 26.7-53.3%; P>0.05) and cleavage (E, 12.8-40.6%; S, 16.1-41.9%; P>0.05), regardless of oocyte age. The actions of both strontium and ethanol were influenced by oocyte age: ethanol induced greater activation rates after 28 and 30 h of maturation (48.4 and 66.7% versus 20.0 and 23.3% for 24 and 26 h, respectively; P<0.05) and strontium after 30 h (53.3%) was superior to 24 and 26 h (26.7% for both). Blastocyst development rates were minimal in all treatments (0.0-6.3%; P>0.05), however, when the mean (+/-S.D.) cell number in blastocysts at the same maturational period was compared, strontium treatment was superior to ethanol for activation rates (82+/-5.7 and 89.5+/-7.8 versus 54 and 61, at 28 and 30 h, respectively). Improved results were obtained by combined treatments. The combination of ethanol and strontium resulted in similar pronuclear formation (ES, 36.7-83.9%; SE, 53.1-90.3%) and cleavage rates (ES, 31.3-81.3%; SE, 65.6-80.7%). Regarding embryo development, there was no difference (P>0.05) between treatments, and blastocysts were only obtained in treatment SE at 24 and 26 h (6.5% for both). It is concluded that, SrCl(2) induces activation and parthenogenetic development in bovine oocytes.

Effects of post-treatment with 6-Dimethylaminopurine (6-DMAP) on ethanol activation of mouse oocytes at different ages

To study the effect of post-treatment with 6-Dimethylaminopurine (6-DMAP) on oocyte activation and development, mouse oocytes collected at different times post human chorion gonadotropin (hCG) injection were incubated in 6-DMAP-containing Chatot-Ziomek-Bavister (CZB) medium for different periods after ethanol exposure, and activation and development were observed. When oocytes were cultured in 6-DMAP without prior ethanol exposure, the highest activation rate was only 40%. Incubation in 6-DMAP for 6 h following ethanol exposure significantly (P < 0.05) increased the activation rate in oocytes recovered 15 and 18 h post hCG, but this effect was not significant in the 21 h oocytes. When oocytes were incubated in 6-DMAP for 1 h at different time points after ethanol, a 6-DMAP susceptible temporal window was found to be located from the second to the fifth h in the 18 h oocytes and from the fourth to the fifth h in the 15 h oocytes, and within the window, the duration of 6-DMAP incubation can be reduced to 0.5 h with more than 80% activation. With the 13 h oocytes, however, 6-DMAP-incubation can only be shortened to 3 h and no specific temporal window was identified. Oocytes that were incubated in 6-DMAP for 1 or 2 h after ethanol exposure developed to morula/blastocyst stages at significantly (P < 0.05) higher rates than those incubated in 6-DMAP for 6 h. Our results suggested that (i) long duration of 6-DMAP incubation impaired the development of mouse parthenogenotes; (ii) the effect of 6-DMAP alone was limited without prior ethanol exposure; (iii) the egg age affected both the timing of 6-DMAP susceptibility and the duration of exposure required to obtain a maximal activating effect; (iv) the most effective activating protocols varied for oocytes of different ages.

Bovine parthenogenesis is characterized by abnormal chromosomal complements: implications for maternal and paternal co-dependence during early bovine development

The present study was conducted to examine the karyotypes of parthenogenetic bovine embryos arising from the application of standard oocyte activation and diploidization methods. Bovine cumulusoocyte complexes were collected and matured in vitro for 24 hr prior to oocyte activation with either 5 microM ionomycin or 7% ethanol for 5 min. Groups of activated oocytes were further treated with 5 micrograms/ml cytochalasin D or 1.9 mM 6-dimethylaminopurine (DMAP) for 6 hr. Cleavage varied significantly (P < .05) among the treatment groups with 68.0% of the ethanol- and DMAP-treated oocytes dividing. Blastocyst development did not vary with 18.4 +/- 2.5% of all treated oocytes progressing to this stage. Blastocyst development did not occur in groups subjected to oocyte activation alone. Blastocysts displayed haploid (2.3%), diploid (11.4%), tetraploid (40.9%), octaploid (4.5%), and mixoploid chromosomal complements (40.9%). Two-cell stage parthenogenotes resulting from ethanol or ionomycin treatment alone displayed haploid (66.7%), diploid (16.7%), tetraploid (4.2%), and mixoploid (12.5%) complements. Our results demonstrate that diploid bovine parthenogenotes arising from these procedures are a minority, with the majority of parthenogenotes displaying polyploid and mixoploid chromosomal complements. The events contributing to these abnormal chromosomal complements occur as early as completion of the first cell cycle, possibly linking these events with the absence of a paternally supplied centrosome.

Cell allocation and chromosomal complement of parthenogenetic and IVF bovine embryos

Considerable concerns exist regarding the quality of parthenogenetically activated embryos in terms of sufficient numbers of cells comprising the inner cell mass (ICM) and trophectoderm (TE) and the ploidy. Therefore, these two parameters were used to assess the quality of embryos derived from parthenogenetic activation by using calcium ionophore A23187 (CaI) followed by either 6-dimethylaminopurine (6-DMAP, 3.5 hr or 6.5 hr) or cycloheximide (CHX) plus cytochalasin D (CD). The conventional in vitro (IVF) produced embryos served as a control. Double staining of the parthenogenetic blastocysts showed that the total cell number (TC) of embryos from the 6-DMAP 3.5 hr (87.0 +/- 5.3) and CHX+CD (79.0 +/- 6.1) groups was not different (P > 0.05), but was lower than that of control embryos (116.0 +/- 5.8, P < 0.001). The mean ratios of inner cell mass (ICM) and trophectoderm (TE) cells in the 6-DMAP 3.5 hr group (0.57 +/- 0.04) and the control IVF group (0.50 +/- 0. 02) did not differ significantly. Both were higher than those of the CHX+CD group (0.36 +/- 0.02; P < 0.05). Further analysis of chromosomal compositions of developing stage embryos at day four after IVF or parthenogenetic activation demonstrated that prolonged treatment with 6-DMAP for 6.5 hr resulted in a significantly lower percentage of diploid embryos and a significantly higher percentage of abnormal ploidy embryos compared to treatment with 6-DMAP for 3.5 hr or with CHX and IVF. In conclusion, parthenogenetic activation of bovine oocytes with CaI followed by 6-DMAP for 3.5 hr could produce better quality embryos in terms of total cell numbers, the number of cells allocated to the ICM, and the ploidy of embryos.

Parthenogenetic Activation of Mouse Oocytes by Exposure to Strontium as a Source of Cytoplasts for Nuclear Transfer

Cell-cycle phase of the donor and recipient cells at the moment of nuclear transfer influences subsequent development of the reconstituted embryo. In order to study this effect, the precise cell-cycle phase of the recipient oocyte at the time of fusion must be known and this depends on reliable activation of oocytes in a protocol that has a low incidence of spontaneous activation. Mouse oocytes recovered before (8-10 hours post-human chorionic gonadotropin [hCG]) and after ovulation (14 and 18 hours post-hCG) were exposed to strontium ions in calcium magnesium-free M16 culture medium. The effect on development of haploid parthenotes of post-hCG age of the oocyte, the duration of exposure, and strontium concentration in the medium was determined. These experiments established a reliable method of parthogenetic activation of recently ovulated mouse oocytes, involving the culture of oocytes for 60 minutes in 25 mM strontium in a calcium magnesium-free M16 medium. This method of activation was also able to induce activation of preovulatory oocytes after a preincubation period in vitro. Only a low incidence of spontaneous activation was observed if oocytes were recovered before or immediately after ovulation (14 hours after hCG).

Metabolism and cell allocation during parthenogenetic preimplantation mouse development

Diploid parthenogenetic postimplantation mouse embryos, containing two maternal genomes, are characterized by poor development of extraembryonic membranes derived from the trophectoderm and primitive endoderm of the blastocyst. This is thought to be caused by a deficiency of expression of paternally derived imprinted genes. Here we have compared the inner cell mass, from which the primitive endoderm and fetal lineages are derived, and the trophectoderm, which forms a major component of the placenta, in parthenogenetic and fertilized preimplantation embryos. We have also studied the metabolism from the 1-cell to the blastocyst stage. Cell numbers were reduced in the ICM and TE of parthenogenetic blastocysts compared to fertilized blastocysts. This was thought to be due to the increased levels of cell death observed in these lineages. Pyruvate and glucose uptake by parthenogenetic embryos was similar to that by fertilized embryos throughout preimplantation development. However, at the expanded blastocyst stage glucose uptake by parthenogenetic embryos was significantly higher than by fertilized embryos. The implications of the actions of imprinted genes and of X-inactivation is discussed.

Abnormal development of embryonic and extraembryonic cell lineages in parthenogenetic mouse embryos

Parthenogetically activated, diploid mouse oocytes can develop to midgestation stages in utero. However, even these advanced parthenogenones appear to die because of much reduced trophoblast and yolk sac development. Previous studies have compared the general features of parthenogenetic and androgenetic development and determined the fate of uniparental cells in chimeras with normal embryos. These studies led to the concept of genomic imprinting as the cause for developmental failure when either the maternal or the paternal genome is duplicated, with the corresponding deficiency of the other. Genomic imprinting appears to arise during gametogenesis and to act through dosage effects in a set of imprinted genes, whose expression depends on their parental origin. In this study we undertook a more detailed morphological analysis of parthenogenetic development in the mouse and established a classification system to quantify the developmental extent of parthenogenones. We found that the failure of parthenogenones occurred at different times during early postimplantation development, generating a spectrum of concepti which had developed to different extents, with only a small fraction of the embryos reaching advanced somite stages. In all parthenogenones differentiation and proliferation of the trophectoderm and primitive endoderm lineages (both extraembryonic) was abnormal, and in all, even the best-developed parthenogenones, we observed similar deficiencies in the embryonic lineages, especially the mesoderm. Common to all abnormally developed lineages was that the proportion of undifferentiated precursor cells was much reduced, while their differentiated descendants were relatively abundant. We propose, therefore, that the failure of parthenogenones to develop to term is due to abnormal regulation of differentiation and proliferation in both embryonic and extraembryonic lineages. In this hypothesis, the apparent tissue specific defects observed in parthenogenones arise as a consequence of the functional importance of certain tissues (like the trophoblast) early in development. The spectrum of parthenogenones thus appears to reflect critical events in early development, whose regulation are affected by genomic imprinting.

Effect of cumulus cells and exposure period to ethanol on in vitro development of mouse diploid parthenogenones

Cumulus-intact and cumulus-free mouse oocytes were exposed to 7% ethanol for 1, 4 and 7 min, and treated with cytochalasin-B. The activation rate and the proportion of diploid parthenogenones in all groups were not significantly different. After 96 hr in culture, a higher number of blastocysts was obtained when either cumulus-intact or cumulus-free oocytes were exposed for shorter times (1 and 4 min) to ethanol. The presence or absence of cumulus cells at activation had no effect on the percentage of blastocysts. However, at 1 and 4 min ethanol-exposure periods, the parthenogenones derived from cumulus-intact oocytes had a higher number of cells than ones derived from cumulus-free oocytes.

Bovine parthenogenetic blastocysts following in vitro maturation and oocyte activation with ethanol

The appropriate in vitro bovine oocyte maturation and ethanol activation conditions for preimplantation bovine embryo parthenogenetic development to the blastocyst stage were investigated. A 7% ethanol concentration significantly enhanced (P<0.05) the proportion of activated, in vitro-matured bovine oocytes (7% ethanol, 83.4 +/- 3.2% versus 0% ethanol, 63.9 +/- 2.0%). The proportion of activated oocytes was significantly higher (P<0.05) by treatment with 7% ethanol for a minimum of 2 minutes (2 minutes, 89.8 +/- 4.0% versus 0.5 minutes 63.4 +/- 4.9%). Oocyte maturation for periods ranging from 30, 34, 38 and 44 hours resulted in a significant increase (P<0.05) in the proportion of activated oocytes, and in oocytes displaying 2 or 3 pronuclei versus oocytes matured for 26 hours. The proportion of cleaved, activated oocytes (2-cell stage), 4 -cell stage and parthenogenetic morula/blastocysts was significantly higher (P<0.05) within the 34-hour oocyte maturation treatment group. Although the 44-hour oocyte maturation treatment group displayed the highest proportion of activated oocytes with 2 pronuclei, it did not display the highest cleavage frequency, possibly due to the effects of postovulatory aging. Several morphologically normal parthenogenetic bovine blastocysts developed from oocytes that were in vitro matured for 34 hours. The ability to produce such parthenogenetic embryos will eventually facilitate investigation into the role(s) of the maternal and paternal genomes during bovine early development.

The incidence of aneuploidy after single pulse electroactivation of mouse oocytes

A brief electric pulse often produces a high rate of activation of recently ovulated oocytes. Some other efficient parthenogenetic stimuli, such as alcohol, however, disrupt the spindle apparatus and increase the incidence of aneuploidy. In this paper, we have determined whether electroactivation per se increases the incidence of chromosomal segregation errors in haploid parthenogenones as evidenced at first cleavage mitosis. Superovulated F1 hybrid female mice were killed at 15.5, 18.5, 22.5, and 25 h after the HCG injection. Batches of 10-12 cumulus-denuded oocytes were transferred to an electroactivation chamber containing mannitol which was connected to a high voltage pulse stimulator and the pulse was triggered once. A high proportion of oocytes activated following this treatment, but only the single-pronuclear haploid parthenogenones were incubated overnight in medium containing colcemid, to determine the incidence of aneuploidy as evidenced at first cleavage mitosis. "Sham" electroactivation groups were also examined for evidence of activation and aneuploidy as described above. In these cases, cumulus-denuded oocytes were put through the electroactivation chamber but the pulse was not triggered. A further group of oocytes was studied to determine the effect of handling and exposure to hyaluronidase on activation frequency and parthenogenetic pathways. Finally, the spontaneous rate of aneuploidy was examined in fertilised embryos of F1 hybrid female mice x Rb(1.3)1Bnr male mice at first cleavage mitosis. The results show that single pulse electroactivation does not increase the level of aneuploidy in single-pronuclear parthenogenous compared to the "sham" group or the spontaneous rate observed in 1-cell fertilised embryos, nor does aneuploidy appear to increase with postovulatory age.(ABSTRACT TRUNCATED AT 250 WORDS)

Developmental potential and chromosome constitution of strontium-induced mouse parthenogenones

The brief exposure of recently ovulated mouse oocytes to M16 embryo culture medium supplemented with strontium chloride (M16 Sr2+) for 2-10 min was observed to induce a high incidence of parthenogenesis. A lower incidence of activation and a significant rate of oocyte degeneration was observed when oocytes were incubated in M16 Sr2+ medium for 20-60 min. The majority of the oocytes exposed to this agent for 2-10 min developed as single-pronuclear haploid parthenogenones. The incidence of this parthenogenetic class was reduced as the duration of exposure to M16 Sr2+ was increased from 2 to 30 min. Under these conditions a greater proportion of the activated oocytes developed as two-pronuclear diploid parthenogenones, due to failure of second polar body extrusion. The activation frequency and the proportionate incidence of the pathways of parthenogenetic development observed following the exposure of ovulated oocytes to calcium-free M16 medium differed significantly from that induced by exposure to M16 Sr2+. Cytogenetic analysis of the single-pronuclear haploid class of Sr(2+)-induced parthenogenones at metaphase of the first-cleavage mitosis has shown that this agent did not induce a significant increase in the incidence of chromosome segregation errors during the completion of the second meiotic division. Analysis of the developmental potential of the two-pronuclear class of diploid Sr(2+)-induced parthenogenones during the preimplantation stages of embryogenesis revealed that their cell number and rate of cell division were less than those of fertilised embryos retained either in vivo or in vitro. The novel methods of activating oocytes indicated in this study present new opportunities to improve the efficiency of embryo cloning techniques with the ruminant species.