Fertilization and cleavage of rhesus monkey oocytes in vitro

Ex utero embryogenesis of non-human primate embryos and beyond

Understanding cellular and molecular processes underlying the human early post-implantation development represents one of the most fundamental questions in development and stem cell biology. As embryos implant into the uterus a week after fertilization, human development beyond the blastocyst stage is extremely difficult to study due to the inaccessibility of embryos and ethical concerns. The advents in the human embryo in vitro culture system provide an easily accessible, tractable, and perturbable platform to dissect key developmental events of human early embryonic development. However, these studies stopped around gastrulation to technical and ethical limitations, and our understanding of human gastrulation and early organogenesis remains poor. As closely related species to humans, non-human primates (NHPs) are suitable surrogate species to interrogate mechanisms underpinning human embryonic development. Here, we review the most recent advances in embryo in vitro culture systems of NHP and discuss their potential optimization strategies and applications.

A Comparison of Oocyte Yield between Ultrasound-Guided and Laparoscopic Oocyte Retrieval in Rhesus Macaques

Obtaining quality oocytes is a prerequisite for ART-based studies. Here we describe a method for transabdominal ultrasound-guided (US) oocyte retrieval in rhesus macaques (Macaca mullata) and compare it to the standard surgical approach using laparoscopy (LAP). We analyzed oocyte yield from six continuous reproductive seasons (2017-2023) that included n = 177 US-guided and n = 136 laparoscopic oocyte retrievals. While the ultrasound-guided technique retrieved significantly fewer oocytes on average (LAP: 40 ± 2 vs. US: 27 ± 1), there was no difference in the number of mature metaphase II oocytes (MII) between the two techniques (LAP: 17 ± 1 vs. US: 15 ± 1). We show that oocytes retrieved by the ultrasound-guided approach fertilize at the same rates as those obtained via the laparoscopic procedure (LAP Fert Rate: 84% ± 2% vs. US Fert Rate: 83% ± 2%). In conclusion, minimally invasive ultrasound-guided oocyte retrieval improves animal welfare while delivering equivalent numbers of mature oocytes, which are ideal for ART. Furthermore, we show that oocyte competency, as represented by fertilization rate, is not affected by retrieval technique. Therefore, the Oregon National Primate Research Center (ONPRC) has adopted the ultrasound-guided approach as the standard technique for oocyte retrieval.

Fertilization and Cleavage Axes Differ In Primates Conceived By Conventional (IVF) Versus Intracytoplasmic Sperm Injection (ICSI)

With nearly ten million babies conceived globally, using assisted reproductive technologies, fundamental questions remain; e.g., How do the sperm and egg DNA unite? Does ICSI have consequences that IVF does not? Here, pronuclear and mitotic events in nonhuman primate zygotes leading to the establishment of polarity are investigated by multidimensional time-lapse video microscopy and immunocytochemistry. Multiplane videos after ICSI show atypical sperm head displacement beneath the oocyte cortex and eccentric para-tangential pronuclear alignment compared to IVF zygotes. Neither fertilization procedure generates incorporation cones. At first interphase, apposed pronuclei align obliquely to the animal-vegetal axis after ICSI, with asymmetric furrows assembling from the male pronucleus. Furrows form within 30° of the animal pole, but typically, not through the ICSI injection site. Membrane flow drives polar bodies and the ICSI site into the furrow. Mitotic spindle imaging suggests para-tangential pronuclear orientation, which initiates random spindle axes and minimal spindle:cortex interactions. Parthenogenetic pronuclei drift centripetally and assemble astral spindles lacking cortical interactions, leading to random furrows through the animal pole. Conversely, androgenotes display cortex-only pronuclear interactions mimicking ICSI. First cleavage axis determination in primates involves dynamic cortex-microtubule interactions among male pronuclei, centrosomal microtubules, and the animal pole, but not the ICSI site.

In Vitro Culture of Embryos from Domestic Cats

A variety of protocols are available for the production of feline blastocysts from oocytes that are matured and fertilized in vitro. However, most of these protocols utilize media that were developed for other cell types or the embryos of other species. The protocol outlined in this chapter is based on a series of studies that led to the development of feline optimized culture medium (FOCM), a feline-specific, sequential medium system. The initial embryo culture medium was subsequently modified for both IVM and IVF. Using a small number of stock solutions, a series of media can be easily prepared that allows for immature cat oocytes to be matured and fertilized in vitro, with the resulting embryos developing to the blastocyst stage without the use of serum.

Assisted reproductive technologies in the common marmoset: an integral species for developing nonhuman primate models of human diseases

Generation of nonhuman primate models of human disease conditions will foster the development of novel therapeutic strategies. Callithrix jacchus, or the common marmoset, is a New World, nonhuman primate species that exhibits great reproductive fitness in captivity with an ovarian cycle that can be easily managed with pharmacological agents. This characteristic, among others, provides an opportunity to employ assisted reproductive technologies to generate embryos that can be genetically manipulated to create a variety of nonhuman primate models for human disease. Here, we review methods to synchronize the marmoset ovarian cycle and stimulate oocyte donors, and compare various protocols for in vitro production of embryos. In light of advances in genomic editing, recent approaches used to generate transgenic or genetically edited embryos in the marmoset and also future perspective are reviewed.

Trophoblast differentiation, invasion and hormone secretion in a three-dimensional in vitro implantation model with rhesus monkey embryos

BACKGROUND

The initiation of primate embryo invasion into the endometrium and the formation of the placenta from trophoblasts, fetal mesenchyme, and vascular components are essential for the establishment of a successful pregnancy. The mechanisms which direct morphogenesis of the chorionic villi, and the interactions between trophectoderm-derived trophoblasts and the fetal mesenchyme to direct these processes during placentation are not well understood due to a dearth of systems to examine and manipulate real-time primate implantation. Here we describe an in vitro three-dimensional (3-D) model to study implantation which utilized IVF-generated rhesus monkey embryos cultured in a Matrigel explant system.

METHODS

Blastocyst stage embryos were embedded in a 3-D microenvironment of a Matrigel carrier and co-cultured with a feeder layer of cells generating conditioned medium. Throughout the course of embryo co-culture embryo growth and secretions were monitored. Embedded embryos were then sectioned and stained for markers of trophoblast function and differentiation.

RESULTS

Signs of implantation were observed including enlargement of the embryo mass, and invasion and proliferation of trophoblast outgrowths. Expression of chorionic gonadotropin defined by immunohistochemical staining, and secretion of chorionic gonadotropin and progesterone coincident with the appearance of trophoblast outgrowths, supported the conclusion that a trophoblast cell lineage formed from implanted embryos. Positive staining for selected markers including Ki67, MHC class I, NeuN, CD31, vonWillebrand Factor and Vimentin, suggest growth and differentiation of the embryo following embedding.

CONCLUSIONS

This 3-D in vitro system will facilitate further study of primate embryo biology, with potential to provide a platform for study of genes related to implantation defects and trophoblast differentiation.

Molecular signatures of bovine embryo developmental competence

Assessment of the developmental capacity of early bovine embryos is still an obstacle. Therefore, the present paper reviews all current knowledge with respect to morphological criteria and environmental factors that affect embryo quality. The molecular signature of an oocyte or embryo is considered to reflect its quality and to predict its subsequent developmental capacity. Therefore, the primary aim of the present review is to provide an overview of reported correlations between molecular signatures and developmental competence. A secondary aim of this paper is to present some new strategies to enable concomitant evaluation of the molecular signatures of specific embryos and individual developmental capacity.

Amphiregulin promotes the maturation of oocytes isolated from the small antral follicles of the rhesus macaque

BACKGROUND

In non-primates, the epidermal growth factor (EGF) and EGF-related ligands such as amphiregulin (AREG) serve as critical intermediates between the theca/mural cells and the cumulus-oocyte-complex (COC) following the mid-cycle LH surge. Studies were designed in primates (1) to analyze AREG levels in follicular fluid (follicular fluid) obtained from pre-ovulatory follicles, as well as (2) to assess dose-dependent effects of AREG on oocytes from small antral follicles (SAFs) during culture, including meiotic and cytoplasmic maturation.

METHODS

Controlled ovulation protocols were performed on rhesus monkeys (n=12) to determine AREG content within the single, naturally selected dominant follicle after an ovulatory stimulus. Using healthy COCs (n=271) obtained from SAFs during spontaneous cycles (n=27), in vitro maturation (IVM) was performed in the absence or presence of physiological concentrations of AREG (10 or 100 ng/ml) with or without gonadotrophins (FSH, 75 mIU/ml; LH, 75 mIU/ml). At the end of the culture period, oocyte meiotic maturation was evaluated and ICSI was performed (n=111), from which fertilization and early embryo development was followed in vitro.

RESULTS

AREG levels in follicular fluid from pre-ovulatory follicles increased (P<0.05) following an ovulatory bolus of hCG at 12, 24 and 36 h post-treatment. At 12 h post-hCG, AREG levels in follicular fluid ranged from 4.8 to 121.4 ng/ml. Rhesus macaque COCs incubated with 10 ng/ml AREG in the presence of gonadotrophins displayed an increased percentage of oocytes that progressed to the metaphase II (MII) stage of meiosis (82 versus 56%, P<0.05) and a decreased percentage of metaphase I (MI) oocytes (2 versus 23%, P<0.05) relative to controls, respectively. The percentage of either MI or MII oocytes at the end of the culture period was not different between oocytes cultured with 100 ng/ml AREG or in media alone. Fertilization and first cleavage rates obtained by ICSI of all IVM MII oocytes were 93 and 98%, respectively, and did not vary among treatment groups. Of the MII oocytes that fertilized (n=103), 37 were randomly selected and maintained in culture to assess developmental potential. A total of 13 early blastocysts were obtained, with four embryos developing to expanded blastocysts.

CONCLUSIONS

These data indicate that AREG levels increase in rhesus macaque pre-ovulatory follicles after an ovulatory stimulus, and a specific concentration of AREG (10 ng/ml) enhances rhesus macaque oocyte nuclear maturation but not cytoplasmic maturation from SAFs obtained during the natural menstrual cycle. However, owing to the small number of samples in some treatment groups, further studies are now required.

Expression profiles of cohesins, shugoshins and spindle assembly checkpoint genes in rhesus macaque oocytes predict their susceptibility for aneuploidy during embryonic development

High frequencies of chromosomal anomalies are reported in human and non-human primate in vitro-produced preimplantation embryos. It is unclear why certain embryos develop aneuploidies while others remain euploid. A differential susceptibility to aneuploidy is most likely a consequence of events that occur before oocyte collection. One hypothesis is that the relative transcript levels of cohesins, shugoshins and spindle assembly checkpoint genes are correlated with the occurrence of chromosomal anomalies. Transcript levels of these genes were quantified in individual oocytes that were either mature (group 1, low aneuploidy rate) or immature (group 2, high aneuploidy rate) at retrieval, utilizing TaqMan-based real-time PCR. The transcript level in each oocyte was categorized as absent, below the median or above the median in order to conduct comparisons. Statistically significant differences were observed between group 1 and group 2 for SGOL1 and BUB1. There were more oocytes with SGOL1 expression levels above the median in group 1, while oocytes lacking BUB1 were only observed in group 1. These findings suggest that higher SGOL1 levels in group 1 oocytes could better protect against a premature separation of sister chromatids than in embryos derived from group 2 oocytes. The absence of BUB1 transcripts in group 1 was frequently associated with reduced expression of either mitotic cohesins or shugoshins. We hypothesize that ablation of BUB1 could induce mitotic arrest in oocytes that fail to express a complete complement of cohesins and shugoshins, thereby reducing the number of developing aneuploid preimplantation embryos.

Utility of animal models for human embryo culture: nonhuman primates

Nonhuman primates are the closest relatives to humans and therefore our most evolutionary close cousins. While marvelous insights are gleaned from studying rodents and other systems, it is impossible to envision how those mechanistic findings can be responsibly translated to the clinic without the appropriate use of nonhuman primates. Thankfully, noninvasive technologies now permit nonhuman primate studies without endangering the model itself. Work with primates is predicted to continue to lead the fields of reproductive and regenerative medicine for the rest of the twenty-first century.

Assisted reproductive technology in nonhuman primates

Nonhuman primates (NHP) are the closest animal species to humans and have been widely used for studying human reproductive physiology. Assisted reproductive technology (ART) in Old World NHPs provides great opportunity for studying fertilization, embryo development, embryonic stem cell (ESC) derivation for regenerative medicine, somatic cell nuclear transfer (cloning), and transgenic NHP models of inherited genetic disorders. Here we present two ART protocols developed for rhesus monkey (Macaca mulatta) and baboon (Papio cynocephalus).

Assisted Reproductive Technologies (ART) with baboons generate live offspring: a nonhuman primate model for ART and reproductive sciences

Human reproduction has benefited significantly by investigating nonhuman primate (NHP) models, especially rhesus macaques. To expand the Old World monkey species available for human reproductive studies, we present protocols in baboons, our closest Old World primate relatives, for assisted reproductive technologies (ART) leading to live born offspring. Baboons complement rhesus by confirming or modifying observations generated in humans often obtained by the study of clinically discarded specimens donated by anonymous infertility patient couples. Here, baboon ART protocols, including oocyte collection, in vitro fertilization (IVF), intracytoplasmic sperm injection (ICSI), preimplantation development to blastocyst stage, and embryo transfer techniques are described. With baboon ART methodologies in place, motility during baboon fertilization was investigated by time-lapse video microscopy (TLVM). The first ART baboons produced by ICSI, a pair of male twins, were delivered naturally at 165 days postgestation. Genetic testing of these twins confirmed their ART parental origins and demonstrated that they are unrelated fraternal twins not identicals. These results have implications for ART outcomes, embryonic stem cell (ESC) derivation, and reproductive sciences.

Cumulus-oocyte complexes from small antral follicles during the early follicular phase of menstrual cycles in rhesus monkeys yield oocytes that reinitiate meiosis and fertilize in vitro

The stage at which follicle-enclosed cumulus-oocyte complexes achieve developmental competence in primates is unknown. Therefore, studies were designed to characterize the ability of oocytes in small antral follicles present during the menstrual cycle to spontaneously resume meiosis, fertilize, and support early embryo development. Ovaries were removed from adult rhesus monkeys (n = 12) during the early follicular phase (Days 3-4) of spontaneous cycles. Small antral follicles were divided into five groups according to their diameter; group I: <0.5 mm; group II: 0.5-0.99 mm; group III: 1.0-1.49 mm; group IV: 1.5-1.99 mm; and group V: 2.0-2.5 mm. The cumulus-oocyte complex from healthy small antral follicles (devoid of dark oocytes or granulosa cells) were extracted (n = 199) and cultured for 48 h under different conditions: in TALP (tyrode, albumin, lactate, pyruvate) medium alone, SAGE medium alone, or plus gonadotropins. At 48 h, oocyte meiotic status and diameter were measured after treatment of cumulus-oocyte complexes with hyaluronidase. Cumulus-oocyte complexes derived from follicles of 0.5- to 2-mm diameter contain oocytes that typically reinitiate meiosis in the absence or presence of gonadotropins and fertilize via in vitro fertilization or intracytoplasmic sperm injection. Moreover, the inseminated oocytes can reach the morula stage but arrest. Thus, the ability of these oocytes to complete maturation, as monitored from subsequent embryonic development after fertilization, is suboptimal. Further studies on primate IVM of oocytes from SAFs are warranted in order for them to be considered as an additional, novel source of gametes for fertility preservation in cancer patients.

Inner cell mass localization of NANOG precedes OCT3/4 in rhesus monkey blastocysts

The mechanism by which the inner cell mass (ICM) and trophectoderm (TE) become specified is poorly understood. Considerable species variation is evident in the expression of lineage-specific and embryonic stem cell (ESC) regulatory markers. We sought to investigate localization patterns of these markers in rhesus macaque compact morulae and blastocysts. NANOG protein was restricted to the ICM of blastocysts. In contrast to a previous report, the expression of CDX2 was detected in the primate blastocyst, localized specifically to the TE. Unlike the mouse embryo, OCT4 protein was detected using two different antibodies in both the ICM and TE. The ubiquitous pattern of OCT4 expression is consistent with observations in human, cow, and pig embryos. Significantly, lack of restricted OCT4 protein, and ICM localization of NANOG in primate blastocysts, suggests that NANOG may determine inner cell mass fate more specifically during primate development or may be less susceptible to culture artifacts. These results contrast markedly with current mechanistic hypotheses, although other factors may lie upstream of NANOG to constitute a complex interactive network. This difference may also underlie observations that regulatory mechanisms in ESC differ between mice and primates.

Early prenatal androgenization results in diminished ovarian reserve in adult female rhesus monkeys

BACKGROUND

Early prenatal androgenization (PA) accelerates follicle differentiation and impairs embryogenesis in adult female rhesus monkeys (Macaca mulatta) undergoing FSH therapy for IVF. To determine whether androgen excess in utero affects follicle development over time, this study examines whether PA exposure, beginning at gestational days 40-44 (early treated) or 100-115 (late treated), alters the decline in serum anti-Mullerian hormone (AMH) levels with age in adult female rhesus monkeys and perturbs their ovarian response to recombinant human FSH (rhFSH) therapy for IVF.

METHODS

Thirteen normal (control), 11 early-treated and 6 late-treated PA adult female monkeys had serum AMH levels measured at random times of the menstrual cycle or anovulatory period. Using some of the same animals, basal serum AMH, gonadotrophins and steroids were also measured in six normal, five early-treated and three late-treated PA female monkeys undergoing FSH therapy for IVF during late-reproductive life (>17 years); serum AMH also was measured on day of HCG administration and at oocyte retrieval.

RESULTS

Serum AMH levels in early-treated PA females declined with age to levels that were significantly lower than those of normal (P < or = 0.05) and late-treated PA females (P < or = 0.025) by late-reproductive life. Serum AMH levels positively predicted numbers of total/mature oocytes retrieved, with early-treated PA females having the lowest serum AMH levels, fewest oocytes retrieved and lowest percentage of females with fertilized oocytes that cleaved.

CONCLUSIONS

Based on these animals, early PA appears to program an exaggerated decline in ovarian reserve with age, suggesting that epigenetically induced hormonal factors during fetal development may influence the cohort size of ovarian follicles after birth.

Incidence of chromosomal mosaicism in morphologically normal nonhuman primate preimplantation embryos

OBJECTIVE

To establish the exact rates of chromosomal mosaicism in morphologically normal rhesus macaque embryos by determining the chromosomal complement of all blastomeres.

DESIGN

Retrospective rhesus monkey IVF study.

SETTING

Academic laboratory and primate research center.

PATIENT(S)

Young fertile rhesus macaque females.

INTERVENTION(S)

Morphologically normal in vitro-produced rhesus macaque embryos were dissociated and cytogenetically assessed using a five-color fluorescent in situ hybridization assay developed for rhesus macaque chromosomes homologous to human chromosomes 13, 16, 18, X, and Y.

MAIN OUTCOME MEASURE(S)

The incidence and extent of chromosomal mosaicism in rhesus macaque preimplantation embryos.

RESULT(S)

Seventy-seven preimplantation embryos, displaying normal morphology and development, from 17 young rhesus macaque females were analyzed. Overall, 39 embryos (50.6%) were normal, 14 embryos (18.2%) were completely abnormal, and 24 embryos (31.2%) were mosaic. Of the 226 blastomeres analyzed in the mosaic group, 110 blastomeres (48.7%) were normal.

CONCLUSION(S)

The observed rate of mosaicism in good-quality rhesus embryos resembles previously documented frequencies in poor-quality human preimplantation embryos. A high incidence of mosaicism may limit the diagnostic accuracy of preimplantation genetic diagnosis.

Postmortem recovery and cryopreservation of spermatozoa from the vas deferens of rhesus macaques (Macaca mulatta)

To determine whether sperm derived from the vas deferens could be retrieved and successfully cryopreserved, testes were collected from 20 rhesus macaques (Macaca mulatta). The males ranged in age from 3 to 19 yr with an average age of 8.5 yr. No sperm was obtained from three animals that were younger than 4 yr. The remaining 17 samples contained sperm with an average sperm cell number of 421.8+/-88.7x10(6) and an average motility of 72.8+/-4.4%. After 24h of culture in TALP medium at 37 degrees C in 5% CO(2) and 95% air, the overall motility decreased significantly in all samples regardless of treatment. Freezing in TEST (TES-Tris buffer)-yolk buffer containing 6% (vol/vol) glycerol had a significant effect on sperm, reducing the immediate postthaw motility to 42.4% in nontreated samples. Treatment with dibutyryl-cAMP and caffeine further reduced sperm motility after 4h in fresh sperm (72.8% vs. 50.4%) but increased motility in sperm that had been frozen (14.0% vs. 23.2%). The age of the male did not influence sperm concentration or grade but proved to be a significant factor in determining motility of frozen-thawed treated sperm, with lower motility found in samples from older males. Overall, the study demonstrates that motile sperm can be obtained from postmortem males, although subsequent studies will be needed to determine whether the quality is sufficient to facilitate its use in assisted reproduction.

Assisted fertilization and embryonic axis formation in higher primates

In naturally fertilized embryos of various organisms, the spermatozoon provides a localized cue to initiate early embryonic patterning. In mice, the sperm entry point (SEP) may reorient the first cleavage division, which separates the zygote into two halves that follow distinct fates. However, it is unknown whether the mechanical injection of spermatozoa into an oocyte by intracytoplasmic sperm injection (ICSI), a technique commonly used in human assisted reproduction, possesses such a role. Rhesus macaque embryos fertilized by ICSI were examined in order to determine the consequences of placing the spermatozoon at specific positions in the ooplasm and whether this can provide new information about patterning in mammalian eggs. The SEP specified by the injected spermatozoa was most often localized near the first cleavage plane and was mainly distributed along the boundary zone that separates the embryonic and abembryonic parts of the monkey blastocyst. Moreover, the ICSI data, when compared with naturally fertilized mouse embryos, showed a similar outcome in terms of cleavage axes and first embryonic axis specification. As there are no studies to date regarding sperm entry in human oocytes and its influence on embryonic development, this investigation using the rhesus macaque as a clinical model is noteworthy.

Role for cumulus cell-produced EGF-like ligands during primate oocyte maturation in vitro

The developmental competence of in vitro-matured (IVM) rhesus macaque cumulus oocyte complexes (COCs) is deficient compared with in vivo-matured (IVM) oocytes. To improve oocyte quality and subsequent embryo development following IVM, culture conditions must be optimized. A series of experiments was undertaken to determine the role of epidermal growth factor (EGF) during IVM of rhesus macaque COCs. The addition of Tyrphostin AG-1478 (a selective inhibitor of the EGF receptor EGFR) to the IVM medium yielded fewer oocytes maturing to metaphase II of meiosis II (MII), decreased cumulus expansion, and a lower percentage of embryos that developed to the blastocyst stage compared with untreated IVM controls, indicating that EGFR activation is important for IVM maturation in the rhesus macaque. However, the addition of recombinant human EGF (r-hEGF) to the IVM medium did not enhance outcome. The expression of mRNAs encoding the EGF-like factors amphiregulin, epiregulin, and betacellulin in cumulus cells indicates that these factors produced by cumulus cells may be responsible for maximal EGFR activation during oocyte maturation, precluding any further effect of exogenous r-hEGF. Additionally, these results illustrate the potential futility of exogenous supplementation of IVM medium without prior knowledge of pathway activity.

Establishment and characterization of baboon embryonic stem cell lines: an Old World Primate model for regeneration and transplantation research

Here we have developed protocols using the baboon as a complementary alternative Old World Primate to rhesus and other macaques which have severe limitations in their availability. Baboons are not limited as research resources, they are evolutionarily closer to humans, and the multiple generations of pedigreed colonies which display complex human disease phenotypes all support their further optimization as an invaluable primate model. Since neither baboon-assisted reproductive technologies nor baboon embryonic stem cells (ESCs) have been reported, here we describe the first derivations and characterization of baboon ESC lines from IVF-generated blastocysts. Two ESCs lines (BabESC-4 and BabESC-15) display ESC morphology, express pluripotency markers (Oct-4, hTert, Nanog, Sox-2, Rex-1, TRA1-60, TRA1-81), and maintain stable euploid female karyotypes with parentage confirmed independently. They have been grown continuously for >430 and 290 days, respectively. Teratomas from both lines have all three germ layers. Availabilities of these BabESCs represent another important resource for stem cell biologists.

Rhesus macaque embryos derived from MI oocytes maturing after retrieval display high rates of chromosomal anomalies

BACKGROUND

Rhesus macaque and human preimplantation embryos display similar rates of chromosomal abnormalities. The aim of this study was to determine whether embryos developing from MI oocytes that mature post-retrieval display more chromosomal anomalies than those embryos that are generated from oocytes that are at MII at the time of retrieval.

METHODS

Rhesus macaque oocytes were obtained after hormonal ovarian stimulation. Immediately after retrieval, the oocytes were classified according to their maturational status. Following in vitro fertilization, Day 3 embryos with good morphology and development derived from oocytes maturing post-retrieval and those from oocytes that were mature at the time of retrieval were cytogenetically assessed using a five-color fluorescent in situ fluorescent hybridization assay developed for rhesus macaque chromosomes homologous to human chromosomes 13, 16, 18, X and Y.

RESULTS

Blastomeres from 53 embryos were analyzed. Of the 27 embryos that developed from oocytes that were mature at collection, 18 embryos were chromosomally normal (66.7%), while from the 26 embryos that developed from oocytes that matured post-retrieval, only 9 embryos were chromosomally normal (34.6%).

CONCLUSIONS

These results indicate that embryos developing from oocytes maturing post-retrieval display high rates of chromosomal abnormalities and have therefore a reduced developmental competence. As a result, the clinical relevance of using immature oocytes that are retrieved after stimulated cycles in human IVF warrants further investigation.

Kinetics of pronuclear development and the effects of vector type and timing of injection on the efficiency of gene transfer into rhesus macaque embryos

A series of experiments was performed to determine the dynamics of pronuclear development as well as the efficiency of either adenovirus-associated (AAV) or lentivirus-derived vectors to introduce a green fluorescent protein (GFP) reporter gene into rhesus macaque (Macaca mulatta) embryos. Assessment of pronuclear development at various times after fertilization revealed that the appearance of pronuclei was determined by the presence of the first and the timing of the second polar body. The dynamics of pronuclear formation was a significant determinant of whether an oocyte reached the blastocyst stage, however, when the percentage of blastocysts were based on the number of zygotes, the timing of the appearance of polar bodies did not appear to have any effect on subsequent development. Injection of different AAV-derived vectors showed that the serotype of the vector did not affect development or the proportion of transgenic embryos. Moreover, all putative transgenic embryos proved to be expression mosaics. Injection of embryos with lentiviral vectors showed that timing of injection (before or after fertilization) had no effect on subsequent transgene expression, but that the type of reporter gene determined post-injection development and rate of transgenesis. The transfer of embryos following injection of a lentiviral vector into three recipients resulted in one pregnancy which was lost during the second trimester. Analysis of fetal tissues showed ubiquitous presence of the transgene and GFP expression in all tissues examined. These results show that lentivirus-derived vectors can efficiently transform rhesus embryos and are suitable for the generation of transgenic rhesus monkeys.

Efficient reproduction of cynomolgus monkey using pronuclear embryo transfer technique

One of the technical bottlenecks in producing nonhuman primate models is that current assisted reproductive techniques, such as in vitro culture and frozen conservation of multicell-stage embryos, often result in poor embryo quality and subsequently lead to low birth rates. We investigated whether pronuclear embryo transfer can be used as an effective means for improving pregnancy and live birth rates of nonhuman primates. We collected 174 metaphase II oocytes by laparoscopy from 22 superovulated mature females and then fertilized these eggs using either in vitro fertilization or intracytoplasmic sperm injection, resulting in a 33.3% and a 50% fertilization rate, respectively. These 66 fertilized pronuclear-stage embryos were then tubally transferred to 30 recipients and led to 7 births and 1 abortion. Importantly, we observed that the highest live birth rate of approximately 64% was obtained when the transfer of pronuclear embryos was performed in the presence of new corpus luteum in the ovary of recipients between 24 h and 36 h after estradiol peak. Therefore, our experiments demonstrate that by matching the critical time window in the recipient's reproductive cycle for achieving optimal embryo-uterine synchrony, pronuclear embryo transfer technology can significantly improve the pregnancy rate and live birth of healthy baby monkeys. This efficient method should be valuable to the systematic efforts in construction of various transgenic primate disease models.

Impairments in embryonic genome activation in rhesus monkey somatic cell nuclear transfer embryos

Somatic cell nuclear transfer (SCNT) is a remarkable process in which a somatic cell nucleus is acted upon by the ooplasm via mechanisms that today remain unknown. Here we show the developmental competence (% blastocyst) of embryos derived from SCNT (21%) was markedly (p < 0.05) impaired compared with those derived from in vitro fertilization (IVF) (42.1%) in rhesus monkey. Also, SCNT embryos were abnormal in their time course of embryonic development. SCNT produced embryos reached the eight-cell stage faster than did IVF produced embryos. We compare the transcription patterns of five nucleolar-related proteins-nucleolin, nucleophosmin, fibrillarin, PAF53, and UBF-in single IVF and SCNT blastocysts by RT-PCR. The SCNT embryos showed abnormal gene transcription. Immunolocalization of fibrillarin was undetectable in 8-cell and 16-cell SCNT embryos, indicating embryonic genomic activation was delayed in monkey embryos produced by SCNT compared to their IVF-derived counterparts. Some of SCNT embryos appeared to relative higher developmental potential and fibrillarin expression by prolonged exposure of incoming nuclei to a cytoplasm. Thus, our data show that SCNT embryos are characterized by abnormal cleavage and the timely onset of embryonic genome transcription, deficits that may explain their reduced pre- and postimplantation developmental capacity.

Chromosomal instability in rhesus macaque preimplantation embryos

OBJECTIVE

To establish a relevant animal model to systematically investigate chromosomal instability in human oocytes and preimplantation embryos.

DESIGN

Prospective rhesus monkey IVF study.

SETTING

Academic laboratory, Oregon National Primate Research Center and Caribbean Primate Research Center.

ANIMAL(S)

Young rhesus macaque females.

INTERVENTION(S)

In vitro produced entire rhesus macaque preimplantation embryos were cytogenetically assessed using a five-color fluorescent in situ hybridization assay developed for rhesus macaque chromosomes homologous to human chromosomes 13, 16, 18, X, and Y, using human bacterial artificial chromosome probes.

MAIN OUTCOME MEASURE(S)

Chromosomal abnormality rates in preimplantation embryos from young rhesus macaque females were established.

RESULT(S)

Fifty preimplantation embryos, displaying good morphology and normal development, were analyzed from 11 young rhesus macaque females. Overall, 27 embryos (54%) were normal, 11 embryos (22%) mosaic, 3 embryos (6%) chaotic, 2 embryos (4%) aneuploid, 3 embryos (6%) haploid, and 4 embryos (8%) triploid.

CONCLUSION(S)

These data indicate that in vitro produced rhesus macaque and human preimplantation embryos exhibit similar numerical chromosomal aberrations. Rhesus macaques appear to be a suitable animal model for investigating the origin of chromosomal instability observed in human preimplantation embryos.

Human blastocyst morphological quality is significantly improved in embryos classified as fast on day 3 (≥10 cells), bringing into question current embryological dogma

OBJECTIVE

To evaluate developmental potential of fast cleaving day 3 embryos.

DESIGN

Retrospective analysis.

SETTING

Academic reproductive center.

PATIENT(S)

Three thousand five hundred twenty-nine embryos.

INTERVENTION(S)

Day 3 embryos were classified according to cell number: slow cleaving: <or=6 cells, intermediate cleaving: 7-9 cells, and fast cleaving: >or=10 cells, and further evaluated on day 5. The preimplantation genetic diagnosis (PGD) results of 43 fast cleaving embryos were correlated to blastocyst formation. Clinical outcomes of transfers involving only fast cleaving embryos (n = 4) were evaluated.

MAIN OUTCOME MEASURE(S)

Blastocyst morphology correlated to day 3 blastomere number. Relationship between euploidy and blastocyst formation of fast cleaving embryos. Implantation, pregnancy (PR), and birth rates resulting from fast embryo transfers.

RESULT(S)

Blastocyst formation rate was significantly greater in the intermediate cleaving (72.7%) and fast cleaving (54.2%) groups when compared to the slow cleaving group (38%). Highest quality blastocysts were formed significantly more often in the fast cleaving group. Twenty fast cleaving embryos that underwent PGD, formed blastocysts, of which 45% (9/20) were diagnosed as euploid. Aneuploidy was diagnosed in 82.6% (19/23) of arrested embryos. A 50% implantation and 100% PR and birth rate were achieved with embryo transfers involving fast cleaving embryos.

CONCLUSION(S)

Fast cleaving embryos not only reach the blastocyst stage at a similar rate to intermediate cleaving embryos, but also exceed morphological quality criteria on day 5. Fast cleaving embryo transfers demonstrated a high clinical potential.

Superovulatory response to a low dose single-daily treatment of rhFSH dissolved in polyvinylpyrrolidone in rhesus monkeys

To simplify the procedure for superovulation in the rhesus monkey, this study was designed using polyvinylpyrrolidone (PVP) solution as a solvent for gonadotropins. Thirty-five cycling females (aged 5-8 years old) were divided into six groups during the breeding season (November- February). The groups were as follows: Group I, animals received twice-daily 35 IU recombinant human follicle-stimulating hormone (rhFSH) dissolved in 0.5 ml saline for 8 days as the control; Groups II and III, animals received single-daily 35 IU and 17 IU rhFSH in 0.5 saline, respectively, for 9 days; Groups IV, V and VI, received single-daily injection of 35 IU rhFSH, 17 IU rhFSH and 8.5 IU rhFSH dissolved in 0.5 ml 30% PVP (w/v) solution, respectively, for 9 days. After human chorionic gonadotropin was administered to induce the nuclear maturation of oocytes, oocytes were retrieved and the development competence of recovered oocytes treated with in vitro fertilization were observed. The plasma concentrations of follicle-stimulating hormone and ovarian responses were monitored during the treatment. The results showed that the number of recovered oocytes and the in vitro developmental competence of mature oocytes was equivalent among monkeys when treated with a single-daily treatment of 17 and 35 IU rhFSH with PVP preparation in Groups IV and V compared with the twice-daily 35 IU rhFSH treatments received by Group I. However, almost all animals in Groups II, III and VI responded poorly to corresponding stimulations. These findings indicate that a single-daily low dose of rhFSH dissolved in PVP solution can induce the satisfactory ovarian responses in rhesus monkeys. This has the potential to reduce treatment distress, stress to the animals, the labor of the operator as well as the amount of rhFSH used in ovarian stimulation, compared with traditional superovulation methods.

Evaluation of the vervet (Clorocebus aethiops) as a model for the assisted reproductive technologies

The vervet monkey was evaluated as a primate model for use in assisted reproductive technologies (ARTs). Eight adult female vervets were hormonally monitored for their potential use as egg donors and those six females displaying regular menstrual cycles were subjected to controlled ovarian stimulation with recombinant human gonadotropins. Three animals failed to respond while laparoscopic follicular aspiration was performed on the other three females at 27-30 h post-human chorionic gonadotropin administration. A total of 62, 40, and 18 oocytes was recovered from these three animals of which 30, 20, and 4, respectively, matured to the metaphase II stage and were subsequently inseminated using intracytoplasmic sperm injection. An average of 40+/-15% (SEM) of the inseminated oocytes were fertilized based on pronucleus formation and timely cleavage. One embryo from each of the two stimulated females developed into expanded blastocysts. Two adult male vervets were assessed as sperm donors. Neither adjusted well to the restraint and collection procedure required for penile electroejaculation. Samples collected via rectal electroejaculation were very low in sperm motility and concentration; however, cauda epididymal aspirations from one male yielded an adequate concentration of motile sperm. These results emphasize the need to establish species-specific ovarian stimulation protocols and semen collection techniques if vervets are to be considered for basic and applied (ARTs) research on primate gametes or embryos.

Prediction of porcine blastocyst formation using morphological, kinetic, and amino acid depletion and appearance criteria determined during the early cleavage of in vitro-produced embryos

The determination for early cleavage-stage embryos of noninvasive morphologic and metabolic criteria that are predictive of blastocyst development and/or full-term viability remains an important research target. We describe the derivation of a logistic regression model that predicts the probability of porcine blastocyst formation in vitro. Pig zygotes, derived by in vitro maturation and fertilization of slaughterhouse oocytes, were cultured in NCSU-23 medium that was supplemented with a mixture of 20 amino acids (NCSU-23(aa)). On Day 1, at 21, 23, 25, 27, 29 and 31 h postinsemination, cleaving embryos were evaluated morphologically in terms of the: i) number of blastomeres, ii) evenness of division, and iii) degree of fragmentation. These embryos were then placed in 1.5-microl drops of NCSU-23(aa) for 24 h, after which time the three morphologic criteria were re-evaluated and 1.2 microl of spent medium were removed for analysis by HPLC, in order to determine the net rates of amino acid depletion and appearance. Embryos were then cultured singly in NCSU-23(aa) by placing them between the filaments of a woven polyester mesh until Day 6, in order to permit the identification of individual embryos. Of 256 cleaved embryos, 28.7 +/- 6.2% (n = 5 replicates) developed into blastocysts. Discriminant analysis was used to select a subset of amino acids (threonine, valine, lysine, and phenylalanine) that discriminated optimally between embryos that became blastocysts or degenerated. These discriminant scores were entered into the logistic regression. Significant univariate relationships were established between the probability of blastocyst development and amino acid score (odds ratio [OR] 0.53, 95% confidence interval [CI] 0.40-0.69, P < 0.001), cleavage time (OR 0.79, 95% CI 0.71-0.87, P < 0.001), degree of fragmentation on Day 1 (OR 0.55, 95% CI 0.35-0.84, P = 0.009) and Day 2 (OR 0.53, 95% CI 0.35-0.78, P = 0.002), evenness of division on Day 2 (OR 0.66, 95% CI 0.46-0.96, P = 0.028), and categorical values of blastomere number on Day 2 (all P < 0.02), although no single variate could accurately predict blastocyst formation. However, multivariate analysis of the cell numbers on Day 1 and Day 2 correctly classified 51.9% of the predicted blastocysts. The inclusion of cleavage time in the regression analysis raised this rate to 63.5%, which was increased to 66.2% by the addition of evenness of division and degree of fragmentation. Finally, the full logistic regression model, which incorporated amino acid score together with all the other morphologic and kinetic variables, correctly classified 80.8% of the predicted blastocysts. This represented 51.2% of the observed blastocysts. Our data are novel in that they not only define in a quantitative manner the influence of previously undescribed predictors of porcine blastocyst formation, but they also provide a simple model of preimplantation development with reasonable predictive accuracy. The present study also provides a basic model for the examination and incorporation of additional early morphologic and metabolic correlates of developmental competence and could potentially be applied to the selection of human embryos for transfer in clinical IVF.

Male-to-male differences in post-thaw motility of rhesus spermatozoa after cryopreservation of replicate ejaculates

BACKGROUND

The efficiency of controlled propagation to produce rhesus monkeys of particular genotypes can be maximized by use of cryopreserved spermatozoa collected from specific males to inseminate appropriate females. But this assumes that semen from males with different genotypes can be cryopreserved with equal effectiveness.

METHODS

To investigate whether spermatozoa from different Macaca mulatta males can be effectively cryopreserved when frozen under identical conditions, we collected and froze semen specimens from 13 adult, fertile males maintained at three primate research centers.

RESULTS

Survival, based on post-thaw motility normalized to the pre-freeze value, was assayed within 30 minutes after thawing; it varied from 50% to 70% but declined thereafter. To examine the response of semen from individual males, we collected and froze three to six ejaculates per male from each of seven males.

CONCLUSIONS

In general, semen from a given male responded reproducibly to freezing, but there were significant differences among males. The cause of these differences among M. mulatta males in post-thaw sperm survival remains unidentified.

Prevention of zona hardening in non-human primate oocytes cultured in protein-free medium

BACKGROUND

Development of a protein-free medium for in vitro maturation of oocytes that prevents zona hardening is essential for the study of components that affect the maturation process.

METHODS

Immature macaque oocytes were cultured in modified CMRL medium with serum protein or without protein [with or without polyvinyl alcohol (PVA)] for 24 hours.

RESULTS

Sperm penetration of oocytes cultured for 24 hours prior to insemination was poor in CMRL medium alone, but was dramatically improved in CMRL medium with the addition of either PVA or BCS. In the second experiment, in vivo matured oocytes were cultured in CMRL with PVA or serum for 6 hours prior to insemination. The incidence of fertilization and embryo development to the blastocyst stage were similar in CMRL with PVA.

CONCLUSIONS

These results indicate that fertilization failure occurs when macaque oocytes are cultured in medium without protein, but can be prevented with PVA.

Effects of rhFSH dose on ovarian follicular response, oocyte recovery and embryo development in rhesus monkeys

The objective was to study the effects of dose of recombinant human follicular stimulating hormone (rhFSH) for ovarian stimulation in rhesus monkeys. Nineteen pubertal and 109 adult female rhesus monkeys were given 37.5, 18, or 9 IU of rhFSH twice-daily for 8 days (total of 600, 300, or 150 IU of rhFSH per cycle, respectively; designated Regimens 1, 2 and 3). Ovarian responses were assessed with ultrasonography, serum concentrations of E2 and FSH, and by in vitro developmental potential (following IVF) of retrieved oocytes. Regimen 1 had more monkeys with very large follicles (diameter>8 mm) than Regimen 2 (P<0.05), which impaired development potential. However, there were no differences between Regimens 1 and 2 in oocyte recovery, whereas Regimen 3 did not elicit superovulation. The developmental potential of embryos obtained from Regimen 2 was higher than that of Regimen 1, as determined by culture to the blastocyst stage in vitro (proportion of blastocysts relative to collected MII oocytes was 55.8% versus 36.8% in pubertal and 63.8% versus 44.2% in adult monkeys; P<0.05 for each), and the results of embryo transfer from Regimen 2 were acceptable. In conclusion, we inferred that the optimal rhFSH dose for ovarian stimulation in rhesus monkeys was a total of 300 IU; this dose should be efficacious for ovarian stimulation as the quality or recovered oocytes was higher and the risk of overstimulation was reduced.

Ultrasound-guided follicular aspiration in squirrel monkeys

The objective of this study was to test whether ultrasound-guided oocyte retrieval is an effective mechanism for collecting oocytes in squirrel monkeys. Although ultrasound-guided follicular aspiration has been described in Old World primates, oocyte retrieval in New World primates is typically performed via laparoscopy or laparotomy. However, these procedures, especially the first, can be invasive. Ultrasound has been used for pregnancy monitoring in multiple species of primates including Saimiri spp. Transabdominal ultrasound as a diagnostic tool is non-invasive. Transabdominal ultrasound was utilized to visualize ovarian follicles during aspiration under light anesthesia. This procedure resulted in collection of a total of 29 oocytes from six animals with minimal post-procedural pain. Manipulated animals were returned to the social group the same day.

Effect of the Timing of First Cleavage on In Vitro Developmental Potential of Nuclear-Transferred Bovine Oocytes Receiving Cumulus and Fibroblast Cells

The aim of the present study was to examine whether cumulus and fibroblast cell nuclear-transferred oocytes, which have high and low potential to develop into normal calves, respectively, are different in terms of in their patterns of timing of first cleavage and in their relationships between timing of first cleavage and in vitro developmental potential. The timing of first cleavage was similar in both types of nuclear-transferred and in vitro fertilized oocytes. More than 86% of the oocytes cleaved within 24 h after activation or in vitro fertilization; these oocytes contributed to more than 98% of the total number of blastocysts in all three groups. The potential of oocytes that cleaved at different intervals to develop into blastocysts differed among the groups. The developmental potential of the cumulus cell nuclear-transferred oocytes and in vitro fertilized oocytes decreased with the increase in time required for cleavage. Fibroblast cell nuclear-transferred oocytes that cleaved at 20 h, an intermediate cleaving time, had higher potential to develop into blastocysts. The results of the present study suggest that the type of donor nucleus used for nuclear transfer affects the timing of first cleavage.

Epigenetic Marks in Cloned Rhesus Monkey Embryos: Comparison with Counterparts Produced In Vitro1

Until now, no primate animals have been successfully cloned to birth with somatic cell nuclear transfer (SCNT) procedures, and little is known about the molecular events that occurred in the reconstructed embryos during preimplantation development. In many SCNT cases, epigenetic reprogramming of the donor nuclei after transfer into enucleated oocytes was hypothesized to be crucial to the reestablishment of embryonic totipotency. In the present study, we focused on two major epigenetic marks, DNA methylation and histone H3 lysine 9 (H3K9) acetylation, which we examined by indirect immunofluorescence and confocal laser scanning microscopy. During preimplantation development, 67% of two-cell- and 50% of eight-cell-cloned embryos showed higher DNA methylation levels than their in vitro fertilization (IVF) counterparts, which undergo gradual demethylation until the early morula stage. Moreover, whereas an asymmetric distribution of DNA methylation was established in an IVF blastocysts with a lower methylation level in the inner cell mass (ICM) than in the trophectoderm, in most cloned blastocysts, ICM cells maintained a high degree of methylation. Finally, two donor cell lines (S11 and S1-04) that showed a higher level of H3K9 acetylation supported more blastocyst formation after nuclear transfer than the other cell line (S1-03), with a relatively low level of acetylation staining. In conclusion, we propose that abnormal DNA methylation patterns contribute to the poor quality of cloned preimplantation embryos and may be one of the obstacles to successful cloning in primates.

In vitro fertilization in the pigtailed macaque (Macaca nemestrina)

The objective of this study was to investigate the possibility of collecting oocytes and semen from pigtailed macaques (Macaca nemestrina) and to establish a protocol for the production of viable embryos that would be suitable for transfer into surrogate females. A total of 82 oocytes were collected from a total of four females (on 2 d with two females each). Semen was collected from the same male on both occasions with respective ejaculate volumes of 0.55 and 0.1 mL containing 2 x 10(9) and 6.6 x 10(8)sperm/mL. Following insemination and after 48 h in culture, 42 (51.2%) of the oocytes had cleaved. Of these, 21 were selected based on developmental stage and their morphology and cryopreserved. The remainder was kept in culture for an additional 5 d, at which time three had reached the expanded blastocyst stage. A total of five transfers were performed with frozen-thawed embryos; two of these resulted in pregnancies and the birth of infants. The results of this study demonstrated that oocytes can be retrieved from pigtailed macaques and that such oocytes can be inseminated and cultured in vitro to the blastocyst stage and give rise to viable offspring after transfer into surrogate females.

A comparative approach to somatic cell nuclear transfer in the rhesus monkey

BACKGROUND

Despite the potential utility of primate somatic cell nuclear transfer (SCNT) to biomedical research and to the production of autologous embryonic stem (ES) cells for cell- or tissue-based therapy, a reliable method for SCNT is not yet available. Employing the rhesus monkey as a clinically relevant animal model, we have compared a conventional electrofusion method for SCNT with a one-step micromanipulation (OSM) method.

METHODS

A prospective, randomized trial was conducted using only oocytes that were mature [metaphase II (MII)] at collection and a fibroblast-like cell line as nuclear donor cells (fetal fibroblasts). The embryos produced were characterized for in vitro developmental potential, cell number, karyotype and expression of nuclear mitotic apparatus (NuMA) and OCT-4.

RESULTS

An in vitro blastocyst development rate of 24.4% was achieved with the OSM method, significantly higher than the 12.2% obtained following electrofusion. SCNT-produced embryos expressed normal karyotypes, cell numbers and NuMA and OCT-4 proteins in most cases. SCNT with male nuclear donor cells resulted in the production of male, SCNT blastocysts, eliminating the possibility of a parthenogenetic origin. Of the four fibroblast cell lines tested as nuclear donor cells, two supported the routine production of blastocysts following SCNT.

CONCLUSIONS

The application of a modified SCNT technique (OSM) followed by embryo culture in hamster embryo culture medium-10 (HECM-10) allows, for the first time, the routine production of SCNT blastocysts, most of which appear normal by immunochemical, cytochemical and in vitro developmental criteria. These embryos will provide a resource for isolating ES cells and for studies of nuclear reprogramming by monkey cytoplasts.

Neonatal behavior and infant cognitive development in rhesus macaques produced by assisted reproductive technologies

Assisted reproductive technologies (ART) used in fertility clinics include in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI), followed by embryo transfer into the biological or a surrogate mother. Over 1,000,000 liveborn offspring--an estimated 1 in 150 United States newborns--have been produced worldwide by ART since 1978. IVF appears to produce healthy children in singleton pregnancies, though concerns remain regarding preterm deliveries, multiple pregnancies, as well as the longer-term consequences of all ART procedures. Clinical studies remain difficult to interpret and subject to confounding variables, as developmental problems may be due to a parent's reproductive conditions rather than, or in addition to, an ART procedure. Also, because of expense and time commitments, the United States ART clinical population is not fully representative of society diversities. This socio-economic skewing might compensate for negative effects, masking small, or modest developmental deficits. Embryo splitting (ES), an ART procedure used only with animals, can produce genetically identical offspring. ES involves dividing four- to eight-cell embryos into separate blastomeres and implanting them into empty zona pellucida, followed by embryo transfer. Although these ART techniques have produced nonhuman primate offspring, there has been no research on behavioral safety. Here, we report the first study of behavioral development by rhesus macaques infants produced through ES, ICSI, and IVF. We assessed neonatal reflexes, self-feeding ability, recognition memory, object concept attainment, simple discrimination learning and reversal, and learning set (LS) acquisition. Although the sample sizes are small, we found no overall ART group delayed development. Surprisingly, the ES and ICSI monkeys appeared to be accelerated in attaining age milestones involving sensory-motor behaviors and a difficult Well Hiding object concept task. We conclude that macaque monkeys may provide an excellent model for the study of early human development by offspring of parents with conditions requiring ART pregnancies, as well as a model for the behavioral study of genetic-environment interactions using identical twins produced by ES.

Effect of culture environment on gene expression and developmental characteristics in IVF-derived embryos

It is generally accepted that mammalian preimplantation embryos are sensitive to their environment and that conditions of culture can affect future growth and developmental potential both pre- and postnatally. Evidence suggests that while culture conditions during bovine in vitro embryo production can impact somewhat 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 period affecting blastocyst quality assessed in terms of cryotolerance, gene expression pattern and ability to establish a pregnancy. This paper reviews the current literature, with emphasis on the bovine model, demonstrating evidence for an effect of post fertilization culture environment on embryo gene expression and quality.

Developmental competence of transported in-vitro matured macaque oocytes

This study examines in-vitro maturation (IVM) in a non-human primate model, Macaca fascicularis. The animals had hormonal injections and laparoscopic oocyte retrieval (OR)) at 12- and 24- h after human chorionic gonadotrophin (HCG). The immature oocytes were placed in tightly capped tubes containing pre-equilibrated IVM medium and transported for 5 h in a dry portable 37 degrees C incubator without CO2 supplement. Meiotic spindle was observed at 36-38- h post-HCG by polarized microscopy in 72 and 84.5% of mature oocytes collected at 12- and 24- h post-HCG oocyte retrieval intervals respectively. However, abnormal spindle formations were detected in some IVM oocytes by confocal microscopy. The IVM oocytes were also randomly selected for (i) intracytoplasmic injection with frozen-thawed epididymal M. fascicularis spermatozoa and (ii) nuclear transfer (NT) with fresh M. fascicularis cumulus cells. Embryonic development of sperm-injected embryos was not affected by the 12- and 24- h post-HCG oocyte retrieval intervals (22.5 versus 27.9% respectively). However, embryonic development of NT embryos was significantly affected by the 12- h post-HCG oocyte retrieval interval (4.5 versus 31.7% respectively; P < 0.01). In conclusion, IVM of monkey oocytes in a dry portable incubator for 5 h did not affect the maturation rate. However, the ability of primate oocytes to develop after somatic cell nuclear transfer was affected by oocyte retrieval time post-HCG.

Mitochondrial DNA deletions in rhesus macaque oocytes and embryos

Mitochondria are the most abundant organelles in mammalian oocytes and early embryos. Mitochondrial DNA (mtDNA) mutations, including the common deletion, have been found in skeletal muscle fibres from aged rhesus macaques. The specific aims of this study were to determine whether the mitochondrial common deletion is present in rhesus oocytes after hormonal stimulation and in embryos generated by in vitro production, or whether this deletion is already present in the immature oocyte. Using a nested primer PCR strategy, we found a significant increase in the proportion of mtDNA deletions in stimulated oocytes and embryos from rhesus macaques, compared with mtDNA deletions in immature, unstimulated oocytes derived from necropsied ovaries of age-matched monkeys. The common deletion is larger in the rhesus (5704 bp) than in humans (4977 bp). Accumulation of mtDNA deletions in oocytes may contribute to mitochondrial dysfunction and impaired ATP production. We propose the rhesus to be an excellent model to assess the quality of gametes and embryos and their developmental competence in primates, including humans.

Low temperature storage of rhesus monkey spermatozoa and fertility evaluation by intracytoplasmic injection

The objective was to develop a sperm freezing procedure suitable for use in the propagation of valuable founder animals by assisted reproductive technologies. Here, we report a comparison of processing methods by measuring the motility of fresh and frozen-thawed rhesus monkey spermatozoa and fertility via intracytoplasmic spermatozoa injection (ICSI) of sibling oocytes. Washed spermatozoa were frozen in straws or in pellets using different cryoprotective media and processed post-thaw with or without a density gradient centrifugation step. Among the four study series, motility post-thaw was improved with density gradient centrifugation (17-24% versus 75%, P<0.01) achieving levels similar to fresh spermatozoa. Spermatozoa injected oocytes (total n=377) were co-cultured on BRL cells and observed for fertilization and development. With spermatozoa frozen in straws in liquid nitrogen vapors, the fertilization rate after ICSI was lower than with fresh spermatozoa (40-44% versus 77-86%, P<0.05), even with the Percoll-enriched fraction that exhibited robust motility. In contrast, somewhat slower freezing of spermatozoa in pellets on dry ice supported fertilization rates (73%) that were similar to the fresh counterpart. Developmental rates of fertilized eggs were similar in all experiments. A total of 106 embryo transfers has resulted in the first primate born after ICSI with F/T ejaculated spermatozoa plus 22 other infants to date. Additionally, a 3-4 h incubation after thawing improved the fertilization rate with spermatozoa from a male with poor post-thaw recovery of sperm motility. In conclusion, an acceptable fertilization rate after ICSI with motile, frozen-thawed primate spermatozoa was observed comparable to that obtained with fresh spermatozoa allowing small quantities of competent spermatozoa to be used with ICSI to facilitate propagation of desirable primate genotypes.

Interactions of macaque blastocysts with epithelial cells in vitro

BACKGROUND

Early in vitro studies of blastocyst formation in several primate species have demonstrated the feasibility of such studies. Initial studies of in vitro-fertilized oocytes cultured with buffalo rat liver cells suggested that other epithelial cells might be used to assess blastocyst adherence and penetration in vitro.

METHODS

Macaque blastocysts were incubated with different epithelial cell lines or with Matrigel. The interaction was studied using light and transmission electron microscopy.

RESULTS

In general, zona-free blastocysts attached 2 days after placing on the substrates. MDCK cells provided optimal conditions for blastocyst development. The best preparations showed some development of an amniotic cavity and distribution of cytotrophoblast and syncytial trophoblast. Distribution of syncytial trophoblast at the margin of the site and cytotrophoblast centrally was similar to that seen at the trophoblastic plate stage in this species. However, there was less syncytial trophoblast than is normally found at this stage, and total time from fertilization to the trophoblastic plate stage was delayed 2 days.

CONCLUSIONS

While in vitro studies with blastocysts cannot completely mimic the intrauterine environment, they can illustrate some of the potential interactions and provide a situation in which parameters may be manipulated.