Yasunari Seita

Generation of Live Rats Produced by In Vitro Fertilization Using Cryopreserved Spermatozoa

Abstract In rats, the success of in vitro fertilization (IVF) was reported 40 years ago. Although it has been demonstrated in papers that these IVF oocytes using sperm freshly collected from cauda epididymides can be developed to term via embryo transfer, successful IVF with cryopreserved rat sperm has never been reported to date. Here, we report establishment of a successful IVF system using frozen/thawed rat spermatozoa. Our data showed that intracellular cAMP and free cholesterol levels in frozen/thawed rat sperm were maintained low, suppressing capacitation-associated tyrosine phosphorylation. The treatment of methyl-beta-cyclodextrin improved removal of free cholesterol from the membrane in frozen/thawed sperm but not induction of capacitation-associated tyrosine phosphorylation in the sperm. Treatment with a phosphodiesterase inhibitor, 3-isobutyl-1-methyl-xanthin (IBMX), dramatically increased cAMP and tyrosine phosphorylation levels in frozen/thawed rat sperm. When the IBMX-treated frozen/thawed sperm were used for IVF, the proportions of pronuclear formation and blastocyst formation were significantly higher than those of frozen/thawed sperm treated without IBMX (P < 0.05). The embryos were developed to term at a high success rate equivalent to the rate obtained with IVF using fresh sperm. Thus, we established for the first time a successful IVF system in rats using cryopreserved spermatozoa.

Molecular characteristics of horse phospholipase C zeta (PLCζ).

A sperm-specific phospholipase C (PLC), PLCzeta (PLCζ), is thought to underlie the initiation of calcium ([Ca(2+) ]i ) oscillations that induce egg activation in mammals. In large domestic species, only bovine, porcine and recently equine PLCζ have been cloned, and the physiological functions of these molecules have not been fully characterized. Here, we evaluated the physiological functions of equine PLCζ (ePLCζ) in mouse oocytes. ePLCζ was cloned from testis using RT-PCR. The expression of ePLCζ messenger RNA was confirmed in testis but not in other tissues. Microinjection of ePLCζ complementary RNA (cRNA) into mouse oocytes induced long-lasting [Ca(2+) ]i oscillations, and most of the injected oocytes formed pronuclei (PN). The injection of cRNAs encoding horse, mouse, human and cow PLCζ into mouse oocytes showed that ePLCζ had the highest [Ca(2+) ]i oscillation-inducing activity among the species tested. Mutation of D202R, which renders the protein inactive, abrogated the activity of ePLCζ. The nuclear translocation ability of ePLCζ was defective when expressed in mouse oocytes. Taken together, our findings show for the first time that ePLCζ has highest activity of the mammalian species studied to date. Our findings will be useful for the improvement of reproductive technologies in the horse.

Expression and immunodetection of aquaporin 1 (AQP1) in canine spermatozoa

The permeability of water and cryoprotectants through the plasma membrane is very important for cryopreservation of mammalian cells. Aquaporin 1 (AQP1) is one of the water channel proteins localized on the membranes of various cells including reproductive organs, allowing water to flow rapidly across the plasma membranes in the direction of osmotic gradients. Although mRNA expression of AQP1 was reported in the mammalian testis by reverse transcription polymerase chain reaction (RT-PCR), protein and mRNA expressions of AQP1 have not been confirmed to date in the sperm of any species. The present study was conducted to determine whether AQP1 mRNA is expressed and AQP1 protein exists in canine spermatozoa. Results from RT-PCR showed that AQP1 mRNA was expressed in canine spermatozoa as well as the testis. The size was similar to the one from canine genomic DNA as a positive control. In sperm, AQP1 protein was also detected by canine AQP1 specific antibody. From these results, both AQP1 mRNA and protein are expressed in male gamete in the dog. Expression of AQP1 may be involved in the flux of water during the cryopreservation of spermatozoa.

A combined treatment with ethanol and 6-dimethylaminopurine is effective for the activation and further embryonic development of oocytes from Sprague-Dawley and Wistar rats.

In nuclear-transferred or round spermatid-injected oocytes, artificial activation is required for further development in mammals. Although strontium chloride is widely used as the reagent for inducing oocyte activation in mice, the optimal method for oocyte activation remains controversial in rats because ovulated rat oocytes are spontaneously activated in vitro before artificial activation is applied. In our previous study, we found that cytostatic factor activity, which is indispensable for arrest at the MII stage, is potentially low in rats and that this activity differs greatly between two outbred rats (Slc: Sprague-Dawley (SD) and Crj: Wistar). Therefore, it is necessary to establish an optimal protocol for oocyte activation independent of strains. Given that comparative studies of the in vitro development of oocytes activated by different activation protocols are very limited, we compared four different protocols for oocyte activation (ethanol, ionomycin, strontium and electrical pulses) in two different SD and Wistar rats. Our results show that oocytes derived from SD rats have significantly higher cleavage and blastocyst formation than those from Wistar rats independent of activation regimes. In both types of rat, ethanol treatment provided significantly higher developmental ability at cleavage and blastocyst formation compared to the other activation protocols. However, the initial culture in a fertilization medium (high osmolarity mR1ECM) for 24 h showed a detrimental effect on the further in vitro development of parthenogenetic rat oocytes. Taken together, our results show that ethanol treatment is the optimal protocol for the activation of rat oocytes in SD and Wistar outbred rats. Our data also suggest that high-osmolarity media are inadequate for the in vitro development of parthenogenetically activated oocytes compared with fertilized oocytes.

Successful cryopreservation of rat pronuclear-stage embryos by rapid cooling

Embryo cryopreservation is a valuable tool for efficient production of animals as well as banking of genetic resources. Even though the laboratory rat is one of the most important experimental animals for various research fields, it has been reported that survival and developmental ability of cryopreserved rat embryos are generally low, especially at the early stages. The aim of the present study was to establish rapid cooling method that can be applied for cryopreservation of rat pronuclear-stage embryos using Cryotops (a device). First, optimal equilibration time was examined. Pronuclear-stage embryos were equilibrated in 7.5% ethylene glycol (EG)+7.5% dimethylsulfoxide (DMSO)+20% fetal calf serum (FCS) for 7, 8 or 9 min at 20-22 degrees C and then 15% EG+15% DMSO+0.5M sucrose+20% FCS for 1 min at 20-22 degrees C, being plunged into liquid nitrogen on Cryotops. This established that development to the 2-cell (82.0+/-9.7% to 96.1+/-3.0%) and blastocyst (36.5+/-2.1% to 40.3+/-10.2%) stages in vitro was not influenced by the equilibration time. Furthermore development to term in vivo (56.0+/-4.9%) was equivalent to the rate (54.8+/-6.6%) obtained with control embryos. Taken together, this demonstrated that this method is suitable for the successful cryopreservation of pronuclear-stage embryos in rats.

Full-term development of rats from oocytes fertilized in vitro using cryopreserved ejaculated sperm.

For preservation of rat spermatozoa, the general-purpose method requires that the male be sacrificed for collection of spermatozoa from the epididymides. However, it would be highly useful if the ejaculated spermatozoa could be successfully cryopreserved and the frozen-thawed spermatozoa used for in vitro fertilization, since this would allow the genetically valuable rats to be maintained alive rather than sacrificed. The aim of the present study was to clarify whether ejaculated rat spermatozoa could be successfully cryopreserved and fertilized in vitro. The motility and viability of frozen-thawed ejaculated spermatozoa were similar to those of frozen-thawed epididymal spermatozoa (around 10%). The percentage of acrosomal integrity in epididymal spermatozoa was significantly higher than that in ejaculated spermatozoa after freezing/thawing. The level of capacitation-associated protein tyrosine phosphorylation in frozen-thawed ejaculated sperm was slightly increased at 5h. When the frozen-thawed ejaculated spermatozoa were used for in vitro fertilization, the percentages of fertilization, pronuclear formation, and development to the 2-cell stage (26.5%, 23.0%, and 91.0%, respectively) were similar to those of frozen-thawed epididymal spermatozoa (19.4%, 15.0%, and 84.1%, respectively). However, the rate of blastocyst formation in the ejaculated group was significantly lower than that in the epididymal group (12.0% vs 43.2%). Results from the embryo transfer experiment showed that the proportions of embryos developed to term were similar between the ejaculated (47.7%) and epididymal groups (53.7%). We showed here for the first time that ejaculated spermatozoa can be cryopreserved and the frozen-thawed sperm could be developed to term via in vitro fertilization in rats.

Techniques for in vitro and in vivo fertilization in the rat.

Although in vitro and in vivo fertilization are powerful tools for restoring conserved sperm as well as stocked males in the rat, the techniques have progressively gained importance. However, the techniques are not used extensively for efficient production of rat offspring, because the techniques require a great deal of skill. This chapter describes the protocols for in vitro and in vivo fertilization in the rat. Namely, sperm collection, sperm cryopreservation, pre-incubation of sperm, and insemination (co-culture with sperm and oocytes) for in vitro fertilization and intrauterine insemination for in vivo fertilization with fresh or frozen/thawed spermatozoa are provided.

Ethnic Differences in Fertility and Assisted Reproduction: Ethnic Disparity in Stem Cell Availability and Research

In addition to the great promise for tissue replacement therapies, research on human embryonic stem cells provides insights into developmental mechanism of disease. However, the lack of diversity in pluripotent stem cell lines limits the discovery for the mechanism of diseases with known ethnic disparities. It also reduces the chance for minority groups to be the recipients of stem cell treatments. In this article, we discuss the current status of the racial disparity in available stem cells, including hematopoietic stem cells from both bone marrow and cord blood, as well as pluripotent stem cells. The application of pluripotent stem cells, as tools for investigating the mechanism of racially implicated disease conditions is proposed. We also report the derivation of 12 African-American iPS cell lines as an initial effort to address the disparity in the availability of pluripotent stem cells for minority populations.

297 Birth of live rats through in vitro fertilization using cryopreserved spermatozoa: sperm fertility improved by freezing at - 150C.

We previously reported that damages to spermatozoa by cold shock can be avoided by cooling slowly at 0.5°C/min to 5.0°C (Seita et al. 2005 Reprod. Fertil. Dev. 17, 277-278). The objective of the present study was to develop an in vitro fertilization (IVF) system with frozen-thawed rat spermatozoa for more efficient reproduction of live offspring. We examined the effect of freezing temperatures (cooling 5.0°C to pre-plunging) on post-thaw sperm motility, plasma membrane integrity, and fertility in vitro. Epididymal spermatozoa of Wistar rats were collected in 2.0 mL of freezing medium containing 23% (v/v) egg yolk, 8.0% (w/v) lactose monohydrate, and 0.7% (v/v) Equex STM (Nova Animal Sales, Inc., Scituate, MA, USA) at room temperature. Samples were loaded into 0.25-mL straws and cooled to 5.0°C at 0.5°C/min in a programmable freezer. Next, the samples were exposed to liquid nitrogen (LN) vapor at various freezing temperatures (-120°C, -150°C or -180°C) above the LN level for 15 min and then plunged into LN. Straws were thawed in a 37°C water bath for 10 min. The thawed samples were diluted to 0.5-1.5 × 106 sperm/mL in a droplet of 200 ¼L of R1ECM and then pre-incubated for 5 h. Ovulated oocytes were introduced into the droplet and co-cultured for 10 h. The oocytes were denuded, fixed, and/or examined for two pronuclei (2PN) formation microscopically. The denuded oocytes, which were fertilized with spermatozoa frozen at -150°C and were microscopically confirmed to have 2PN formation, were transferred to pseudo-pregnant recipient females. IVF was also performed by the same method using fresh spermatozoa as the control. Differences in the sperm motility and plasma membrane integrity were analyzed by ANOVA, and the IVF data were analyzed by chi-square test. At 2 h after thawing the motility of spermatozoa frozen at -150°C was significantly higher than that of spermatozoa frozen at -180°C (19.8% and 11.1%; P 0.05). The percentage of oocytes with 2PN was not significantly different between the -150°C frozen and the control (fresh spermatozoa) groups [59% (131/221) and 62% (155/251); P > 0.05], although that of frozen spermatozoa at -120°C and -180°C [20% (38/188) and 23% (35/153)] were significantly lower than that of frozen spermatozoa at -150°C (P < 0.05). A total of 168 putative fertilized zygotes with 2PN were transferred to eleven recipients, and 87 live young were born. In conclusion, our results indicated that post-thaw motility of cryopreserved rat spermatozoa was improved by using a suitable cooling protocol, and the IVF system used in the present study would effectively produce offspring from the cryopreserved epididymal rat spermatozoa. To our knowledge, this procedure is the first successful production of live offspring from cryopreserved rat spermatozoa through in vitro fertilization.

279 LIVE RAT OFFSPRING FROM CRYOPRESERVED EJACULATED SPERMATOZOA THROUGH IN VITRO FERTILIZATION

We have previously reported successful cryopreservation of epididymal rat spermatozoa (Nakatsukasa et al. 2001 Reproduction 122, 463). However, the procedure for cryopreservation of rat spermatozoa has a disadvantage; a male has to be euthanized for collection of spermatozoa from its epididymides. Obtaining ejaculated spermatozoa repeatedly from the same male could be useful for cryopreservation of invaluable spermatozoa which carry mutations including transgenes. The objective of the present study was to develop a reliable system for cryopreservation of ejaculated rat spermatozoa and efficient production of offspring from the cryopreserved spermatozoa. Matured Wistar females were mated with three males of the same strain, and killed by cervical dislocation after formation of vaginal plugs. The uteri of mated females were excised and flushed with freezing medium containing 23.0% egg yolk, 8.0% lactose, and 0.7% Equex STM to recover ejaculated spermatozoa. The semen samples were loaded into 0.25-mL straws. The straws were cooled to 5.0°C at 0.5°C/min in a programmable freezer and then exposed to liquid nitrogen (LN) vapor at 4 cm (-150°C) above the LN level for 15 min. The straws were then plunged into LN and stored for at least a week. The straws were thawed in a 37.0°C water bath for 10 min. The thawed samples were diluted to 0.5-1.5 × 106 sperm/mL into a 200-¼L droplet of R1ECM and then pre-incubated for 5 h. Ovulated oocytes collected from superovulated females were introduced into the droplet and co-cultured for 10 h for in vitro fertilization (IVF). The oocytes were denuded and examined for the presence of two pronuclei (2PN) microscopically. The denuded oocytes with 2PN were transferred into the oviducts of pseudo-pregnant females. The rates of sperm motility at recovery, post-thaw, and the initiation of IVF (after pre-incubation) were 57 ± 6%, 24 ± 5%, and 18 ± 3%, respectively. After co-culture, 46 (14%) of the total 329 co-cultured oocytes were confirmed to contain 2PN. A total of the 44 putative zygotes were transferred to five recipients, and a total of 21 live young (48%) were born from all of the transferred recipients. We were able to produce zygotes and offspring derived from cryopreserved ejaculated spermatozoa of all three males used in the present study. In conclusion, the cryopreservation system for ejaculated rat spermatozoa used in the present study is a workable protocol for banking of valuable genetic resources of laboratory rats. Further studies on the IVF procedure with cryopreserved ejaculated spermatozoa in the rat are needed to improve the fertilization rate.