In vitro maturation and development of porcine oocytes cultured in a straw or dish using a portable incubator with a CO2 chamber

We investigated the effects of a portable incubator with a CO(2) chamber on the viability and development of porcine oocytes/embryos for their transportation and examined the operational suitability of a straw or dish as a container for culturing the oocytes or embryos in the portable incubator. In the first experiment, the cumulus-oocyte complexes (COCs) were placed either in a dish or straw; and they were then cultured for 44 h in a standard CO(2) incubator, in the CO(2) chamber in an incubator, or in the CO(2) chamber in a portable incubator. The matured oocytes were fertilized with frozen-thawed spermatozoa and then cultured in a dish in the standard CO(2) incubator for 8 days. There were no differences in the proportions of oocytes reaching metaphase II stage among the groups. However, the proportions of cleavage and development to blastocysts derived from oocytes matured in a straw were lower than those from oocytes matured in a dish, irrespective of the type of incubator used. In the second experiment, the COCs were matured in a dish in the standard CO(2) incubator, and the matured oocytes were fertilized and then placed either in a dish or straw. These were then cultured for 8 days in the standard CO(2) incubator or portable incubator. Some zygotes cultured in the portable incubator developed to the blastocyst stage. The proportions of cleavage and development to blastocysts were significantly lower for putative zygotes cultured in straw than for those cultured in dish, irrespective of the type of incubator used. Our results indicate that a portable incubator with a CO(2) chamber can maintain the viability and development of oocytes/embryos, but the straw is not a suitable system for in vitro culture of the oocytes/embryos during transportation.

Nuclear replacement of in vitro-matured porcine oocytes by a serial centrifugation and fusion method

The objective of the present study was to establish a method for nuclear replacement in metaphase-II (M-II) stage porcine oocytes. Karyoplasts containing M-II chromosomes (K) and cytoplasts without chromosomes (C) were produced from in vitro-matured oocytes by a serial centrifugation method. The oocytes were then reconstructed by fusion of one karyoplast with 1, 2, 3 or 4 cytoplasts (K + 1C, K + 2C, K + 3C and K + 4C, respectively). Reconstructed oocytes, karyoplasts without fusion of any cytoplast (K) and zona-free M-II oocytes (control) were used for experiments. The rates of female pronucleus formation after parthenogenetic activation in all groups of reconstructed oocytes (58.2-77.4%) were not different from those of the K and control groups (58.2% and 66.0%, respectively). In vitro fertilization was carried out to assay the fertilization ability and subsequent embryonic development of the reconstructed oocytes. The cytoplast : karyoplast ratio did not affect the fertilization status (penetration and male pronuclear formation rates) of the oocytes. A significantly high monospermy rate was found in K oocytes (p < 0.05, 61.6%) compared with the other groups (18.2-32.8%). Blastocyst formation rates increased significantly as the number of the cytoplasts fused with karyoplasts increased (p < 0.05, 0.0-15.3%). The blastocyst rate in the K + 4C group (15.3%) was comparable with that of the control (17.8%). Total cell numbers in both the K + 3C and K + 4C groups (16.0 and 15.3 cells, respectively) were comparable with that of the control (26.2 cells). Our results demonstrate that a serial centrifugation and fusion (Centri-Fusion) is an effective method for producing M-II chromosome transferred oocytes with normal fertilization ability and in vitro development. It is suggested that the number of cytoplasts fused with a karyoplast plays a critical role in embryonic development.

Topographic analysis of the inferior parietal lobule in high-resolution 3D MR imaging

BACKGROUND AND PURPOSE

Recent functional MR imaging studies have revealed that the inferior parietal lobule (IPL) supports numerous functions; however, the precise organization of the IPL remains unclear. It has been previously reported that the individual components of the IPL show variable morphologic features; thus, any investigations of IPL function must take into account the variable topography of the IPL. However, it is difficult to understand the topography of the IPL only in transaxial and/or sagittal MR images. We generated volume rendering (VR) images of the brain from high-resolution 3D MR imaging data and analyzed the topography of the IPL.

MATERIALS AND METHODS

Forty healthy volunteers were examined with 1.5T MR imaging, and VR images were generated. Sulcal continuity, sulcal connections, and the gyral pattern of the IPL were investigated.

RESULTS

The main sulci and gyri were able to be identified excellently on VR images of all volunteers. One long, continuous postcentral sulcus (postCS) was seen in 47.5% and 40% in the right and left hemisphere, respectively. The frequency with which the postCS connected with the anterior end of the IPS was 72.5% and 75% in the right and left, respectively. The gyral pattern of the IPL showed variable morphology.

CONCLUSIONS

VR images can depict the sulcal continuity and connections of the IPL accurately. VR imaging is a very useful noninvasive technique to observe the topography of the IPL and should contribute to the investigation of functional localization.

Generation of porcine diploid blastocysts after injection of spermatozoa grown in nude mice

It is anticipated that the utilization of spermatogonia through testicular xenografting will open new avenues for the conservation of male gametes. With the aim of establishing this new technique for genetic preservation of pigs, we used it in combination with intracytoplasmic sperm injection (ICSI). Testicular tissues derived from neonatal piglets, which contained seminiferous cords consisting of only gonocytes/spermatogonia, were transplanted under the back skin of castrated nude mice. Between 125 and 192 d after xenografting, sperm (morphologically similar to epididymal sperm) were recovered from 41 of the 65 host mice (63.1%). Testicular spermatozoa from adult boars were used as a positive control. A single spermatozoon was injected into an in vitro matured porcine oocyte, and the oocytes were electro-stimulated and cultured (graft-ICSI and testis-ICSI, respectively). Blastocyst rates in both ICSI groups (24.9% and 37.4%, respectively) were higher (P<0.05) than those without the injection procedure (parthenogenetic; 12.7%) and after injection of a small amount of injection buffer (sham; 13.0%). Rates of diploid blastocysts in both graft-ICSI and testis-ICSI groups (48.9% and 60.6%) were higher (P<0.05) than those in the parthenogenetic and sham groups (13.5% and 28.0%). Therefore, we demonstrated that porcine oocytes injected with xenogeneic sperm have in vitro developmental ability to the blastocyst stage.

270 PRETREATMENTS OF PORCINE SPERM BEFORE INTRACYTOPLASMIC SPERM INJECTION AFFECT QUANTITY OF PLCZETA;

In pigs, the intracytoplasmic sperm injection (ICSI) procedure alone is insufficient to induce oocyte activation for embryonic development. Artificial activation can be accomplished, such as by electrical pulse-enhanced in vitro development to the blastocyst stage (Nakai et al. 2006). It is well known that the sperm factor (phospholipase Cζ; PLCζ) in spermatozoa, which triggers oocyte activation, is diffused into ooplasm when sperm fuse with oocytes. Our previous study showed that the activation rate of porcine oocytes injected with one sonicated sperm head was significantly lower than that of oocytes injected with a whole spermatozoon or with 3 sonicated sperm heads (Nakai et al. IETS 2007). These results suggest that the sonication treatment per se may affect the quantity of PLCζ in sperm. Furthermore, various pretreatments of sperm besides sonication have been conducted (e.g. removal of the sperm membrane) to increase the efficacy of ICSI. In this study, we investigated the effect of pretreatments (sonication, Triton X-100, and repeated cycles of freezing–thawing without cryoprotectant) on the quantity of PLCζ in porcine sperm. Cryopreserved-thawed boar-ejaculated sperm were used for 3 experimental groups: (1) sperm were sonicated for 10 s in pig-fertilization medium (pig-FM; Suzuki et al. 2002; Soni group), (2) freezing–thawing was repeated 3 times in pig-FM without cryoprotectant (3-F/T group), or (3) sperm were incubated in pig-FM supplemented with 0.1 or 1% Triton X-100 at 37°C for 1 min (0.1 and 1% Triton X-100 groups, respectively). Cryopreserved-thawed whole sperm without any treatment was used as a control. Results from staining with fluorescein diacetate and propidium iodide showed that almost all sperm were propidium iodide positive (dead sperm) immediately after the each treatment. In the control group, approximately 40% of sperm were fluorescein diacetate positive (live sperm) after thawing. The presence of PLCζ (72 kDa) was examined by Western blotting using the antibody against the N-terminal 19-mer sequence of porcine PLCζ (Kurokawa et al. 2005). A band corresponding to porcine PLCζ was not detected in any treatment group in any culture period (from 0 to 135 min). In contrast, PLCζ was detected in the control group and in all culture periods. These results strongly suggest that PLCζ in porcine sperm was lost immediately after the pretreatments, such as by sonication, incubation with 0.1 or 1% Triton X-100, and repeated cycles of freezing–thawing. The decrease in PLCζ protein by pretreatment may be one of the causes of incomplete activation of oocytes in porcine ICSI. This work was supported by a Grant-in-Aid for JSPS Fellows.

Appearance, fate and utilization of abnormal porcine embryos produced by in vitro maturation and fertilization

In vitro production (IVP) including in vitro maturation (IVM) and fertilization (IVF) is now an important technology for obtaining live piglets. However, there are still two significant obstacles to the efficient production of viable porcine embryos: (1) polyspermy and (2) fertilization of oocytes arrested at the immature stage. These phenomena relate to production of embryos with abnormal ploidy (polyploidy). To avoid these problems, careful selection of mature oocytes for IVF, and regular monitoring of normal and abnormal fertilization (polyspermy and/or lack of male pronucleus formation) are very important. In our recent studies, however, we have confirmed that some oocytes with abnormal ploidy after polyspermy can develop into diploid embryos with potentially normal developmental ability. The mechanism by which such fertilized polyploid oocytes develop to a normal state during embryo development is still not well understood. Attempts to clarify this mechanism would hopefully reveal data that are very useful for not only IVP but also other technologies such as the production of transgenic or cloned animals using IVM oocytes, including other species, also for human reproductive manipulation. In this review, we focus on studies of normality of IVM oocytes and ploidy of IVP embryos, and try to suggest practical ways of solving the problems mentioned above in pigs.

[Off-pump coronary artery bypass grafting as standard operation; surgical strategies and results]

We report the clinical results of 799 cases of isolated coronary artery bypass grafting (CABG) performed during the recent 5 years. We performed off-pump CABG (OPCAB) as standard operation, in which arterial grafts were mainly used. The mean number of distal anastomoses was 3.6 +/- 1.4 per patient Four hundred and fifty-five cases (57.0%) were done only with arterial grafts. Bilateral internal thoracic arteries were used in 326 cases. The mean number of saphenous vein grafts was 1.6 +/- 0.8 per patient. Continuous hemodiafiltraion (CHDF) was performed in 22 cases (2.8%) postoperatively. Among the OPCAB cases, 10 cases (1.3%) were converted to on-pump CABG. There were 7 cases (0.9%) of hospital death. The mean length of postoperative hospital stay was 10.2 +/- 5.3 days. The ratio of the patients with left main trunk disease and that of the patients who required postoperative CHDF increased year by year. The mean length of postoperative hospital stay decreased every year, and the reduced length was 2.7 days in the 5 years (8.7+/- 3.6 days in 2007). It is expected that patients who have severe calcified lesions or who are on hemodialysis may increase in the near future. In such cases, CABG rather than percutaneous catheter intervention may be suitable for revascularization. Therefore, not only appropriate choice of treatment strategies, but also accurate surgical techniques may become more importance.

Selected aspects of advanced porcine reproductive technology

In vitro fertilization (IVF) of in vitro matured (IVM) oocytes in pigs has become the most popular method of studying gametogenesis and embryogenesis in this species. Furthermore, because of recent advances in in vitro culture (IVC) of IVM-IVF embryos, in vitro production (IVP) of embryos now enables us to generate viable embryos as successfully as for in vivo-derived embryos and with less cost and in less time. These technologies contribute not only to developments in reproductive physiology and agriculture but also to the conservation of porcine genetic resources and the production of cloned or genetically modified pigs. However, in IVP, there still remains the problem of abnormal ploidy, which is caused by performing procedures under non-physiological conditions. In recent years, unique technologies such as intracytoplasmic sperm injection (ICSI) or xenografting of gonadal tissue into immunodeficient experimental animals have been developed to help conserve gamete resources. These technologies combined with IVP are expected to be useful for the conservation of gametes from important genetic resources. Here, we discuss the developmental ability and normality of porcine IVP embryos and also the utilization of ICSI and xenografting in advancing biotechnology in pigs.

Effects of an automated stride assistance system on walking parameters and muscular glucose metabolism in elderly adults

OBJECTIVE

To identify the effects of an automated stride assistance system (SAS) on walking scores and muscle activities in the lower extremities of elderly people.

METHODS

Seven healthy elderly men (73-81 years) participated in this study. Subjects walked continuously at a constant speed for 50 min on a treadmill with and without the SAS, which is a device to control the walk ratio (step length/cadence) and to add support power to the thigh during walking. A step counter equipped with an infrared device was used to record walking data. The average speeds during treadmill walking were 2.89-3.82 km/h without the SAS and 3.03-4.03 km/h with the SAS. Positron emission tomography (PET) and [18F]fluorodeoxyglucose (FDG) evaluation of glucose metabolism were conducted on each subject twice after walking with and without the SAS.

RESULTS

Walk ratio, walking speed and step length were significantly improved in all subjects by the SAS, while cadence was significantly decreased by the SAS in all subjects except one. The SAS did not have a significant effect on glucose metabolism of the muscles of the lower extremities. There were no significant correlations between change in walking speed and change in glucose metabolism in each muscle without the SAS and with the SAS. In contrast, significant correlations between walking speed and glucose metabolism were shown in gluteus minimus (r = -0.929), hip-related muscles (r = -0.862), soleus (r = -0.907), and medial gastrocnemius (r = -0.952) without the SAS. With the SAS, there were significant correlations in gluteus medius (r = -0.899), hip-related muscles (r = -0.819), and medial gastrocnemius (r = -0.817) in the elderly subjects.

CONCLUSIONS

The SAS increases walking scores in elderly people without increasing energy consumption of lower-extremity muscles. The elderly subjects with low walking speed showed higher glucose metabolism in hip-related muscles and triceps surae. Thus, this association suggested that decreased walking speed in elderly adults has a higher metabolic cost in these muscle regions.

Long pulse production of high current D(-) ion beams in the JT-60 negative ion source

The first long pulse production of high power D(-) ion beams has been demonstrated in the JT-60 U negative ion sources, each of which was designed to produce 22 A, 500 keV D(-) ion beams. Voltage holding capability and the grid power loading were examined for long pulse production of high power D(-) ion beams. From the correlation between voltage holding and the light intensity of cathodoluminescence from the Fiber Reinforced Plastic insulators, the acceleration voltage for stable voltage holding capability was found to be less than 320-340 kV where the light was sufficiently suppressed. By tuning the extraction voltage, the grid power loadings in the ion sources were decreased to the allowable levels for long pulse injection without a significant reduction of the beam power. After tuning the acceleration and extraction voltages, D(-) ion beams of 12.5 and 9.8 A were produced at 340 keV with cesium seeding at a rate of approximately 14 microg/s into the ion sources. The pulse duration of these D(-) ion beams was extended step by step, and then was successfully extended up to 18 s without degradation of the negative ion production. The D(-) ion beams were neutralized to yield 3.6 MW D(0) beams by a gas cell, and then injected into the JT-60 U plasma. Further, a slight reduction of D(-) ion beam power allowed the longer injection duration of 21 s at a D(0) beam power of 3.2 MW. The success in the long pulse production of a high power D(-) ion beam shows that negative ion beams can be produced during a few tens of seconds without degradations of negative ion production and the voltage holding in a large Cs-seeded negative ion source.

93 PRODUCTION OF LIVE PIGLETS BY CRYOPRESERVATION OF IN VITRO-PRODUCED PORCINE ZYGOTES

Successful cryopreservation of in vitro-produced porcine zygotes is reported in the present study. Follicular oocytes were collected from prepubertal gilts. They were matured (IVM), fertilized (IVF), and cultured (IVC) in vitro (Kikuchi et al. 2002 Biol. Reprod. 66, 1033–1041). Ten or 23 h after IVF, the oocytes were centrifuged at 10 000g at 37�C for 20 min to permit visualization of pronuclei. Zygotes with two or three pronuclei were selected under stereomicroscope and used for solid surface vitrification (SSV). Briefly, after equilibration in 4% ethylene glycol (EG) for 15 min, zygotes were washed in vitrification solution (35% EG, 5% polyvinyl pyrrolidone, and 0.3 m trehalose), and then dropped with about 2 µL vitrification solution onto the dry surface of aluminum foil floating on the surface of liquid nitrogen (LN2). Microdroplets were transferred into cryotubes and stored in LN2. During warming, vitrified droplets were transferred in warming solution (0.4 m trehalose) at 37�C for 1 min, and then consecutively transferred for 1-min periods into 0.2 m, 0.1 m, or 0.05 m trehalose solutions. Survival of vitrified/warmed zygotes was determined by their morphology. To assess their developmental competence, vitrified (SSV), cryoprotectant-treated (CT), and untreated (control) zygotes were cultured in vitro for 6 days. There was no difference in developmental competence between control and CT zygotes in terms of cleavage rates (88.1% and 86.1%, respectively), blastocyst rates (23.2% and 20.8%, respectively), and blastocyst cell numbers (38.0 � 2.0 and 41.2 � 1.7, respectively). The rate of live zygotes after SSV and warming was similar to that of the control (93.4% and 100%, respectively). Cleavage rates (71.7% and 86.3%, respectively) and blastocyst rates (15.8% and 24.5%, respectively) of SSV were significantly reduced after vitrification compared to control (P < 0.05, ANOVA). Blastocyst cell numbers of SSV and control embryos were similar (41.2 � 3.4 and 41.6 � 3.3, respectively). There was no difference in developmental ability between zygotes cryopreserved at an early (10 h after IVF) or late (23 h after IVF) pronuclear stage. When embryo culture medium was supplemented with 1 µm of the antioxidant glutathione, development of cryopreserved zygotes to the blastocyst stage did not differ significantly from that of the control zygotes (18.6% and 22.1%, respectively). To test their ability to develop to term, 150 vitrified zygotes were transferred into a recipient, resulting in pregnancy and the production of five live piglets. These data demonstrate that a high rate of porcine zygotes could be successfully cryopreserved at the pronuclear stage, preserving their full developmental competence.

44 EFFECT OF CYTOPLAST VOLUME ON FERTILIZATION AND EMBRYO DEVELOPMENT IN PORCINE M-II OOCYTES RECONSTRUCTED WITH KARYOPLASTS AND CYTOPLASTS OBTAINED BY THE 'CENTRI-FUSION' METHOD

Metaphase-II chromosome transfer (M-II transfer) of oocytes is considered to be one of the advanced procedures to improve fertilization and developmental abilities of oocytes with poor cytoplasmic maturation. The aim of this study was to investigate the developmental capacity after IVF and IVC of porcine oocytes reconstructed from karyoplasts and cytoplasts produced by centri-fusion (Fahrudin et al. 2007 Cloning Stem Cells 9, 216–228). In brief, IVM oocytes (Kikuchi et al. 2002 Biol. Reprod. 66, 1033–1041) with a visible first polar body were centrifuged at 13 000g for 9 min to stratify the cytoplasm. Then the zonae pellucidae were removed with pronase treatment. Zona-free oocytes were layered on a 300-µL discontinuous gradient of Percoll in TCM-HEPES with 5 µg mL–1 of cytochalasin B. After centrifugation at 6000g for 4 s, fragmented cytoplasms with approximately equal volumes were obtained, stained with Hoechst-33342, and classified into cytoplasm with (K; karyoplast) or without (C; cytoplast) chromosomes. One karyoplast was fused with 0, 1, 2, 3, and 4 cytoplasts (K, K + 1C, K + 2C, K + 3C, and K + 4C, respectively) by an electric stimulation with a single DC pulse (1.5 kV cm–1 for 20 µs) and cultured for 1 h. Zona-free oocytes without any reconstruction served as control oocytes. The diameters of the reconstructed and control oocytes were measured. All specimens were fertilized in vitro with frozen–thawed boar sperm, and cultured using the well of the well (WOW) system (Vajta et al. 2000 Mol. Reprod. Dev. 55, 256–264). Their fertilization status and developmental competence were examined. Data were analyzed by ANOVA followed by Duncan's multiple range tests. The diameter differed significantly among K to K + 4C oocytes (75.0–127.1 µm; P < 0.05), whereas the diameter of K + 2C oocytes was similar to that of the control oocytes (110.5 µm). Regardless of the cytoplast volume, sperm penetration rates (73.1–93.8%) for K to K + 4C oocytes were not significantly different compared to control oocytes (78.0%). Male pronuclear formation rates of K to K + 4C oocytes (92.3–97.1%) were also not different significantly different compared to control oocytes (96.6%). However, monospermy rates of K oocytes was significantly higher (61.6%; P < 0.05) than those of the reconstructed (K + 1C to K + 4C; 18.2–34.9%) and control oocytes (32.9%). The blastocyst formation rates in K, K + 1C, K + 2C, and K + 3C groups (0.0–9.8%; P < 0.05) were significantly lower than those in the control and K + 4C groups (17.8% and 15.3%, respectively; P < 0.05). The total cell numbers per blastocyst in K + 1C and K + 2C groups (7.5 and 8.3 cells, respectively) were significantly lower than in the control, K + 3C, and K + 4C groups (15.3–26.2 cells; P < 0.05). These results suggest that the cytoplast volume of porcine M-II transferred oocytes, produced by reconstruction from a karyoplast and cytoplast(s) and centri-fusion, is important for their ability to develop to the blastocyst stage and influences cell number.

247 EFFECTS OF CYSTEINE IN IVM MEDIA ON IN VITRO MATURATION UNDER LOW OXYGEN TENSION, IN VITRO FERTILIZATION, AND IN VITRO CULTURE OF PORCINE OOCYTES

Cysteine is considered to promote male pronuclear (MPN) formation in porcine through oocyte glutathione (GSH) synthesis (Yoshida et al. 1993 Biol. Reprod. 49, 89–94). The GSH has an important role in providing cells with a redox state and in acting to protect cells from toxic effects of oxidative damage (Meister et al. 1976 AM Rev. Biochem. 45, 559–604). However, such previous investigations were carried out under high O2 tension (20% O2) incubation conditions. Here we simply study IVM-IVF-IVC competence of porcine oocytes matured in IVM media supplemented with cysteine of different concentrations under low oxygen tension (5% O2). Cumulus–oocyte complexes (COCs) from prepubertal gilts were collected, matured, and fertilized in vitro according to Kikuchi et al. (2000 Biol. Reprod. 66, 1033–1041). COCs were cultured in IVM medium supplemented with 0 (Group 1; control), 0.05 (Group 2), 0.1 (Group 3), 0.2 (Group 4), and 0.6 mm (Group 5) cysteine under low oxygen tension. Nuclear maturation of oocytes, fertilization status, and number of cells in resultant embryos were assessed with orcein staining; also, the GSH content of IVM oocytes was measured by the method described by Ozawa et al. (2002 Reproduction 124, 683–689). Maturation rates of Groups 1–5 were 68.2 � 3.2, 70.6 � 7.7, 69.7 � 15.9, 75.9 � 7.7, and 68.8 � 8.0%, respectively, indicating no difference in maturation competence among the groups (P > 0.05 by ANOVA). The rates of sperm penetration, MPN formation (95.9 � 2.4, 100 � 0, 92.8 � 4.7, 94.0 � 4.1, and 92.4 � 2.7%, respectively), monospermy, and even blastocyst rates after 6 days of IVC were not different among the groups (P > 0.05 by ANOVA). Moreover, the cell numbers of blastomeres in blastocysts (38.68 � 3.5, 40.1 � 3.1, 37.5 � 3.0, 36.2 � 3.3, and 43.8 � 4.0, respectively) were uniformly the same among the groups (P > 0.05 by ANOVA). However, GSH content of IVM oocytes increased significantly (P < 0.05 by ANOVA) as the concentration of cysteine increased (12.2 � 0.6, 14 � 0.8, 15.1 � 0.5, 16.4 � 0.4, and 16.4 � 0.5 pmol/oocyte, respectively). The GSH level of oocytes in Group 1 (control) seems to be higher than that reported by Aberydeera et al. (1998 Biol. Reprod. 58, 213–218), who matured porcine oocytes under high O2 tension. This may reflect the effect of low O2 tension and explain the same developmental rate to the blastocyst stage as that of oocytes matured in the media supplemented with cysteine in this study. In conclusion, an addition of 0.05–0.6 mm cysteine during IVM, under 5% O2 tension, of porcine oocytes significantly increased intracellular GSH synthesis according to its concentration. However, it had no promoting effects on nuclear maturation, fertilization, male pronucleus formation, and subsequent embryonic development to the blastocyst stage. Thus, O2 tension during IVM of oocytes is suggested to be important for the in vitro production of porcine blastocysts.

218 DEVELOPMENT OF EVENLY AND UNEVENLY CLEAVED TWO-CELL PORCINE EMBRYOS

Mammalian eggs are so microlecithal that the embryos would be expected to divide in unison and that each division would lead to 2 equal blastomeres, which are believed to have a greater competence for further development than zygotes with unequal cleavage. However, some studies have shown that uneven blastomere size commonly occurs from the very first division in mammals, and it seems to be concerned with the generation of the first cell lineages of the blastocyst cells: trophectoderm and the inner cell mass (Gueth-Hallonet and Maro 1992 Trends Genet. 8, 274–279). In our study, we produced porcine embryos in vitro (Kikuchi et al. 2002 Biol. Reprod. 66, 1031–1041), and newly formed 2-cell embryos were collected. Based on the timing of the first cleavage (30 or 36 h after insemination), the cleavage pattern (E: equal; U: unequal) and the presence or absence of a second cleavage (+ or –) within the first 2 days of IVC was classified into groups: 30E(–), 30E(+), 30U(–), 30U(+), 36E(–), 36E(+), 36U(–), or 36U(+). There was no difference between the 30E and 30U groups in proportions of the 2-cell stage, which had a nucleus in both blastomeres (99.0 � 0.8% and 91.4 � 3.6%, respectively) or between the 36E and 36U groups (98.2 � 1.1% and 88.0 � 7.2%, respectively). Comparison of further development between the 30E and 30U groups showed that there was no difference in blastocyst rates (70.7 � 5.7% and 61.7 � 7.8%, respectively) and total cell numbers (39.1 � 2.1 and 31.7 � 2.3, respectively). Although the blastocyst rate in the 36E group (37.3 � 6.7%) was significantly higher (P < 0.05) than that of the 36U group (12.0 � 5.1%), the total cell number was not different (26.3 � 5.5 and 25.3 � 5.2, respectively). The timing of the first division, however, had a great influence on further development of the embryos; the 30-h cleaved embryos had a greater rate of blastocyst development (68.2 � 6.3%) than did the 36-h embryos (28.2 � 4.8%, P < 0.01 by ANOVA). The cell numbers of blastocysts derived from 30-h cleaved embryos (37.2 � 2.6) were significantly higher than those of the 36-h embryos (26.2 � 2.3, P < 0.01) as well. Two-cell embryos that were newly formed at 30 h and underwent the next cleavage within the first 2 days of IVC (30 + group) had a higher blastocyst rate (74.8 � 7.0%) and greater cell numbers (40.6 � 2.6) than those not showing a second division during this period (30– group; 46.8 � 5.0% and 19.9 � 2.2, respectively). In contrast, for embryos showing the first cleavage at 36 h of insemination, the presence of the next cleavage within 2 days after the first cleavage did not have any effect on embryonic development. These results suggest that the developmental ability of porcine embryos was influenced by the timing and shape of the first cleavage and by the subsequent occurrence of the second cleavage.