Hyaluronic acid as a macromolecular crowding agent for production of cell-derived matrices

Cell-derived matrices (CDMs) provide an exogenous source of human extracellular matrix (ECM), with applications as cell delivery vehicles, substrate coatings for cell attachment and differentiation, and as biomaterial scaffolds. However, commercial application of CDMs has been hindered due to the prolonged culture time required for sufficient ECM accumulation. One approach to increasing matrix deposition in vitro is macromolecular crowding (MMC), which is a biophysical phenomenon that limits the diffusion of ECM precursor proteins, resulting in increased ECM accumulation at the cell layer. Hyaluronic acid (HA), a natural MMC highly expressed in vivo during fetal development, has been shown to play a role in ECM production, but has not been investigated as a macromolecule for increasing cell-mediated ECM deposition in vitro. In the current study, we hypothesized that HA can act as a MMC, and increase cell-mediated ECM production. Human dermal fibroblasts were cultured for 3, 7, or 14 days with 0%, 0.05%, or 0.5% high molecular weight HA. Ficoll 70/400 was used as a positive control. SDS-PAGE, Sircol, and hydroxyproline assays indicated that 0.05% HA-treated cultures had significantly higher mean collagen deposition at 14 days, whereas Ficoll 70/400-treated cultures had significantly lower collagen production compared to the HA and untreated controls. However, fluorescent immunostaining of ECM proteins and quantification of mean gray values did not indicate statistically significant differences in ECM production in HA or Ficoll 70/400-treated cultures compared to untreated controls. Raman imaging (a marker-free spectral imaging method) indicated that HA increased ECM deposition in human dermal fibroblasts. These results are consistent with decreases in CDM stiffness observed in Ficoll 70/400-treated cultures by atomic force microscopy. Overall, these results indicate that there are macromolecule- and cell type- dependent effects on matrix assembly, turnover, and stiffness in cell-derived matrices. STATEMENT OF SIGNIFICANCE: Cell-derived matrices (CDMs) are versatile biomaterials with many regenerative medicine applications, including as cell and drug delivery vehicles and scaffolds for wound healing and tissue regeneration. While CDMs have several advantages, their commercialization has been limited due to the prolonged culture time required to achieve CDM synthesis in vitro. In this study, we explored the use of hyaluronic acid (HA) as a macromolecular crowder in human fibroblast cell cultures to support production of CDM biomaterials. Successful application of macromolecular crowding will allow development of human cell-derived, xeno-free biomaterials that re-capitulate the native human tissue microenvironment.

Relationship between the maturational state of oocytes at the time of insemination and sex ratio of subsequent early bovine embryos

The effect of maturational state of bovine oocytes at the time of insemination on early embryo development and the sex ratio of developing embryos was evaluated. Early maturing oocytes were inseminated either immediately after the first polar body extrusion or insemination was delayed for 8 h. Most of the zygotes completed the first embryonic cell cycle and reached the 2-cell stage by 35 h after insemination regardless of the time of insemination. Delaying insemination enhanced the proportion of cleaving zygotes and significantly improved their development to the 8-cell stage. At the same time delaying insemination produced significantly higher proportions of male embryos. Cleavage and development to 8-cell stage was significantly impaired when oocytes were inseminated immediately after polar body formation. Sex ratio in these embryos did not differ from 1. These results suggest that oocytes developmental ability as well as capability to process X and Y-bearing spermatozoa may be acquired at specific times during maturation.

Fertilization imaged in 2-, 3- and four dimensions: molecular insights for treating infertility

Fertilization in humans follows a complex series of events including binding of the sperm to the oocyte plasma membrane, oocyte activation, the completion of meiotic maturation of the oocyte with the extrusion of the second polar body, the decondensation of the sperm nucleus and the maternal chromosomes into male and female pronuclei and the restoration of the sperm centrosome. This duplicates and separates, forming two mitotic spindle poles upon which the parental genomes can intermix to complete fertilization. The use of intracytoplasmic sperm injection (ICSI) has been highly effective as a treatment for severe male infertility and thousands of ICSI babies have been born world-wide. Working with rhesus monkey gametes, we have developed a preclinical animal model for understanding the cell biological basis of ICSI. Typically, ICSI results in abnormal nuclear remodeling during sperm decondensation due to the presence of the sperm acrosome and perinuclear structures normally removed at the oolemma during in vitro fertilization. These unusual modifications raise concerns that the ICSI procedure itself might lead to the observed increase in chromosome anomalies reported for

Possible mechanism for acceleration of meiotic progression of bovine follicular oocytes by growth factors in vitro

The mechanism for the accelerating effects of epidermal growth factor (EGF) and insulin-like growth factor I (IGF-I) on the meiotic cell cycle of bovine oocytes cultured in vitro was investigated. Cumulus-oocyte complexes (COCs) were obtained from small (< or = 3 mm in diameter), medium (4-6 mm in diameter) or large (7-10 mm in diameter) ovarian follicles and cultured with or without a combination of EGF and IGF-I (growth factors). Growth factors significantly increased the frequency of first polar body extrusion of oocytes derived from small follicles at 16 h of culture (PB16 oocytes; with growth factors: 75%; without growth factors: 55%), but did not increase the frequency in oocytes from medium or large follicles. COCs from small follicles were cultured with individual growth factors and sampled for kinase activity. The frequencies of polar body extrusion in EGF only (67%) and EGF + IGF-I (75%) treatment groups were significantly higher than those in the control (no growth factor) group (49%), but not significantly higher than in the IGF-I only group (63%). The H1 kinase activity at 6-8 h of culture in each group increased significantly from the baseline value at 0 h of culture, and the H1 kinase activities in the EGF only, IGF-I only and EGF + IGF-I treatment groups were significantly higher than those in the control group at 8 h of culture. MAP kinase activity was significantly higher than the baseline value and significantly higher than that in the control group at 6 h of culture in the EGF treatment group only. In conclusion, EGF and IGF-I act on COCs from small follicles to accelerate the meiotic cell cycle of the oocytes. This accelerating effect may be related to increased H1 and MAP kinase activities during the early stages of maturation.

Possible mechanism for acceleration of meiotic progression of bovine follicular oocytes by growth factors in vitro

The mechanism for the accelerating effects of epidermal growth factor (EGF) and insulin-like growth factor I (IGF-I) on the meiotic cell cycle of bovine oocytes cultured in vitro was investigated. Cumulus-oocyte complexes (COCs) were obtained from small (< or = 3 mm in diameter), medium (4-6 mm in diameter) or large (7-10 mm in diameter) ovarian follicles and cultured with or without a combination of EGF and IGF-I (growth factors). Growth factors significantly increased the frequency of first polar body extrusion of oocytes derived from small follicles at 16 h of culture (PB16 oocytes; with growth factors: 75%; without growth factors: 55%), but did not increase the frequency in oocytes from medium or large follicles. COCs from small follicles were cultured with individual growth factors and sampled for kinase activity. The frequencies of polar body extrusion in EGF only (67%) and EGF + IGF-I (75%) treatment groups were significantly higher than those in the control (no growth factor) group (49%), but not significantly higher than in the IGF-I only group (63%). The H1 kinase activity at 6-8 h of culture in each group increased significantly from the baseline value at 0 h of culture, and the H1 kinase activities in the EGF only, IGF-I only and EGF + IGF-I treatment groups were significantly higher than those in the control group at 8 h of culture. MAP kinase activity was significantly higher than the baseline value and significantly higher than that in the control group at 6 h of culture in the EGF treatment group only. In conclusion, EGF and IGF-I act on COCs from small follicles to accelerate the meiotic cell cycle of the oocytes. This accelerating effect may be related to increased H1 and MAP kinase activities during the early stages of maturation.

A putative, ubiquitin-dependent mechanism for the recognition and elimination of defective spermatozoa in the mammalian epididymis

The normal structure and function of sperm are prerequisites for successful fertilization and embryonic development, but little is known about how defective sperm are eliminated during mammalian spermatogenesis. Here, we describe a ubiquitin-dependent, sperm quality control mechanism that resides in the mammalian epididymis, the site of sperm maturation and storage. We used immunofluorescence, electron microscopy, western blotting and pulse-chase experiments to show that ubiquitin is secreted by the epididymal epithelium and binds to the surface of defective sperm. Most of the ubiquitinated sperm are subsequently phagocytosed by the epididymal epithelial cells. A portion of defective sperm escapes phagocytosis and can be found in the ejaculate. Cultured epididymal cells maintain their ability to produce ubiquitin and phagocytose the defective sperm, as well as the ubiquitin-coated microspheres, in vitro. The surprising phenomenon of cell-surface ubiquitination in defective sperm provides a possible mechanism for sperm quality control in mammals and a new marker of semen abnormalities in men and animals.

A combination of EGF and IGF-I accelerates the progression of meiosis in bovine follicular oocytes in vitro and fetal calf serum neutralizes the acceleration effect

The effects of a combination of EGF and IGF-I (GFs) on the progress of meiosis and on their developmental competence were examined in cumulus-enclosed bovine oocytes. Exposure to GFs in serum-free, 0.3% PVP-containing maturation medium significantly (P<0.05) increased the frequency of oocytes with the first polar body (PB) at 16 h of culture and decreased those with PB at 20 h. The cleavage rates of PB-extruded oocytes after fertilization were not affected by treatment of GFs during maturation culture, and blastocyst yield was not improved by GFs treatment. Although replacement of PVP from GFs-containing medium with fatty acid-free BSA did not affect the timing of PB extrusion, replacement with 10% FCS neutralized the acceleration effects of GFs. Replacement for macromolecule in maturation medium did not improve blastocyst yield of PB-extruded oocytes after fertilization. These results indicate that the progression of meiosis in bovine oocytes with cumulus cells is accelerated by exposure to GFs in serum-free maturation medium but their developmental competence is not improved, and that the acceleration effects on the progress of meiosis is neutralized by the presence of FCS in maturation medium with no improvement of developmental competence after in vitro fertilization.

Live rhesus offspring by artificial insemination using fresh sperm and cryopreserved sperm

Artificial insemination (AI) and the cryopreservation of sperm with full reproductive capabilities are vital in the armamentarium of infertility clinics and reproductive laboratories. Notwithstanding the fantastic successes with AI and sperm cryopreservation in numerous species, including humans and cattle, these assisted reproductive technologies are less well developed in other species of importance for biomedical research, such as genetically modified mice and nonhuman primates. To that end, AI at high efficiency in the rhesus macaque (Macaca mullata) and the successful cryopreservation of rhesus sperm is presented here, as are the complexities of this primate model due to differences in reproductive tract anatomy and gamete physiology. Cryopreservation had no effect on the ability of sperm to fertilize oocytes in vitro or in vivo. Post-thaw progressive motility was not affected by cryopreservation; however, acrosome integrity was lower for cryopreserved (74.1%) than for fresh sperm (92.7%). Fertilization rates did not differ when fresh (58.1%; n = 32/55) or cryopreserved sperm (63.8%; n = 23/36) were used for in vitro fertilization. Similarly, pregnancy rates did not differ significantly after AI with fresh (57.1%; n = 8/14) or cryopreserved sperm (62.5%; n = 5/8). Seven live rhesus macaques were born following AI with fresh sperm, and three live offspring and two ongoing pregnancies were obtained when cryopreserved sperm were used. Cryopreservation of rhesus sperm as presented here would allow for the cost-effective storage of lineages of nonhuman primates with known genotypes. These results suggest that either national or international centers could be established as repositories to fill the global needs of sperm for nonhuman primate research and to provide the experimental foundation on which to explore and perfect the preservation of sperm from endangered nonhuman primates.

Ubiquitinated sperm mitochondria, selective proteolysis, and the regulation of mitochondrial inheritance in mammalian embryos

The strictly maternal inheritance of mitochondria and mitochondrial DNA (mtDNA) in mammals is a developmental paradox promoted by an unknown mechanism responsible for the destruction of the sperm mitochondria shortly after fertilization. We have recently reported that the sperm mitochondria are ubiquitinated inside the oocyte cytoplasm and later subjected to proteolysis during preimplantation development (P. Sutovsky et al., Nature 1999; 402:371-372). Here, we provide further evidence for this process by showing that the proteolytic destruction of bull sperm mitochondria inside cow egg cytoplasm depends upon the activity of the universal proteolytic marker, ubiquitin, and the lysosomal apparatus of the egg. Binding of ubiquitin to sperm mitochondria was visualized by monospecific antibodies throughout pronuclear development and during the first embryonic divisions. The recognition and disposal of the ubiquitinated sperm mitochondria was prevented by the microinjection of anti-ubiquitin antibodies and by the treatment of the fertilized zygotes with lysosomotropic agent ammonium chloride. The postfecundal ubiquitination of sperm mitochondria and their destruction was not seen in the hybrid embryos created using cow eggs and sperm of wild cattle, gaur, thus supporting the hypothesis that sperm mitochondrion destruction is species specific. The initial ligation of ubiquitin molecules to sperm mitochondrial membrane proteins, one of which could be prohibitin, occurs during spermatogenesis. Even though the ubiquitin cross-reactivity was transiently lost from the sperm mitochondria during epididymal passage, likely as a result of disulfide bond cross-linking, it was restored and amplified after fertilization. Ubiquitination therefore may represent a mechanism for the elimination of paternal mitochondria during fertilization. Our data have important implications for anthropology, treatment of mitochondrial disorders, and for the new methods of assisted procreation, such as cloning, oocyte cytoplasm donation, and intracytoplasmic sperm injection.

TransgenICSI reviewed: foreign DNA transmission by intracytoplasmic sperm injection in rhesus monkey

This brief review considers the status of transgenesis by intracytoplasmic sperm injection (ICSI) with nonhuman primates. GFP expressing rhesus macaques embryos (mean = 34.6%; N = 81) were produced by ICSI using rhodamine-tagged DNA encoding the green fluorescence protein (GFP) gene bound on sperm. Rhodamine signal was lost at the egg surface during in vitro fertilization (IVF) but could be traced by dynamic imaging during ICSI within the egg cytoplasm. GFP gene was expressed as early as the 4-cell stage in ICSI embryos but not in embryos produced by in vitro fertilization (IVF). The percentage of GFP expressing blastomeres increased during embryogenesis to the blastocyst stage. Three offspring resulted from seven embryo transfers-a set of anatomically normal twins (a male and a female) stillborn 35 days premature, and a healthy male born at term. Although transgene was not detected in the offspring, the successful production of live primates using DNA bound sperm by ICSI suggests an alternative route to creating transgenic animals. It also raises concern regarding transmission of infectious material during ICSI.

Clonal propagation of primate offspring by embryo splitting

Primates that are identical in both nuclear and cytoplasmic components have not been produced by current cloning strategies, yet such identicals represent the ideal model for investigations of human diseases. Here, genetically identical nonhuman embryos were produced as twin and larger sets by separation and reaggregation of blastomeres of cleavage-stage embryos. A total of 368 multiples were created by the splitting of 107 rhesus embryos with four pregnancies established after 13 embryo transfers (31% versus 53% in vitro fertilization controls). The birth of Tetra, a healthy female cloned from a quarter of an embryo, proves that this approach can result in live offspring.

Dynamic imaging of the metaphase II spindle and maternal chromosomesin bovine oocytes: implications for enucleation efficiency verification, avoidanceof parthenogenesis, and successful embryogenesis

Manipulations of DNA and cellular structures are essential for the propagation of genetically identical animals by nuclear transfer. However, none of the steps have been optimized yet. This study reports a protocol that improves live dynamic imaging of the unfertilized bovine oocyte's meiotic spindle microtubules with microinjected polymerization-competent X-rhodamine-tubulin and/or with vital long-wavelength excited DNA fluorochrome Sybr14 so that the maternal chromosomes can be verifiably removed to make enucleated eggs the starting point for cloning. Suitability of the new fluorochromes was compared to the conventional UV excitable Hoechst 33342 fluorochrome. Enucleation removed the smallest amount of cytoplasm (4-7%) and was 100% efficient only when performed under continuous fluorescence, i.e., longer fluorescence exposure. This was in part due to the finding that the second metaphase spindle is frequently displaced (60.7 +/- 10%) from its previously assumed location subjacent to the first polar body. Removal of as much as 24 +/- 3% of the oocyte cytoplasm underneath the polar body, in the absence of fluorochromes, often resulted in enucleation failure (36 +/- 6%). When labeled oocytes were exposed to fluorescence and later activated, development to the blastocyst stage was lowest in the group labeled with Hoechst 33342 (3%), when compared to Sybr14 (19%), rhodamine-tubulin (23%), or unlabeled oocytes (37%). This suggests that longer wavelength fluorochromes can be employed for live visualization of metaphase spindle components, verification of their complete removal during enucleation, and avoidance of the confusion between artifactual parthenogenesis versus "cloning" success, without compromising the oocyte's developmental potential after activation.

Cellular and molecular events after in vitro fertilization and intracytoplasmic sperm injection

Intracytoplasmic sperm injection (ICSI) has heralded an era of tremendous improvements in treating male infertility leading to the births of thousands of babies. However, recent concerns over possible long-term effects of ICSI on offspring has prompted the development of a preclinical, nonhuman primate model to assess the safety of ICSI. Fluorescent imaging of rhesus macaque IVF zygotes revealed that this species shares many similarities with humans in terms of cytoskeletal and chromatin dynamics during fertilization. However, rhesus monkey zygotes fertilized by ICSI resulted in abnormal nuclear remodeling leading to asynchronous chromatin decondensation in the apical region of the sperm head, delaying the onset of DNA synthesis. The persistence of the acrosome and perinuclear theca on the apex of sperm introduced into the oocyte by ICSI may constrict the DNA in this region. Despite these differences, normal rhesus monkey ICSI embryos have been produced and have lead to several births after transfer. The irregularities described in this paper raise concerns that the ICSI procedure may result in chromatin damage during DNA decondensation and further highlight the need for devising improved pre-clinical assessment prior to global acceptance of this, and other, novel methods of assisted reproduction.

Foreign DNA transmission by ICSI: injection of spermatozoa bound with exogenous DNA results in embryonic GFP expression and live rhesus monkey births

Exogenous DNA transfer, mediated by intracytoplasmic sperm injection (ICSI) with plasmid-bound spermatozoa, results in the production of transgene expressing embryos in rhesus macaques (Macaca mulatta, mean = 34.6%; n = 81). Rhodamine-tagged DNA encoding the green fluorescent protein (GFP) gene binds avidly to spermatozoa. The rhodamine signal, while lost at the egg surface during in-vitro fertilization (IVF), is traced by dynamic imaging during ICSI and remains as a brilliant marker on the microinjected spermatozoa within the oocyte cytoplasm. The transgene is expressed in preimplantation embryos produced by ICSI, but not IVF, as early as the 4-cell stage with the number of expressing cells and the percentage of expressing embryos increasing during embryogenesis to the blastocyst stage. The three offspring that resulted from seven embryo transfers (a set of anatomically normal twins, one male and one female, stillborn 35 days premature, and a healthy male born at term) demonstrate that primate spermatozoa with exogenously bound DNA retain their full reproductive capacity in ICSI, but raise the concern that, theoretically, ICSI could transmit infectious material as well.

Optimization Strategies for Production of Mammalian Embryos by Nuclear Transfer

In order to optimize each of the individual steps in the nuclear transfer procedure, we report alternative protocols useful for producing recipient cytoplasts and for improving the success rate of nuclear transfer embryos in cattle, rhesus monkey, and hamster. Vital labeling of maternal chromatin/spindle is accomplished by long wavelength fluorochromes Sybr14 and rhodamine labeled tubulin allowing constant monitoring and verification during enucleation. The use of Chinese hamster ovary (CHO) donor cells expressing the viral influenza hemagglutinin fusion protein (HA-300a+), to adhere and induce fusion between the donor cells and enucleated cow, rhesus and hamster oocytes was examined. Cell surface hemagglutinin was activated with trypsin prior to nuclear transfer and fusion was induced by a short incubation of a newly created nuclear transfer couplet at pH 5.2 at room temperature. Donor cell cytoplasm was dynamically labeled with CMFDA, or further transfected with the green fluorescence protein (GFP) gene, so that fusion could be directly monitored using live imaging. High rates of fusion were observed between CHO donor cells and hamster (100%), rhesus (100%), and cow recipient cytoplasts (81.6%). Live imaging during fusion revealed rapid intermixing of cytoplasmic components between a recipient and a donor cell. Prelabeled donor cytoplasmic components were uniformly distributed throughout the recipient cytoplast, within minutes of fusion, while the newly introduced nucleus remained at the periphery. The fusion process did not induce activation as evidenced by unchanged distribution and density of cortical granules in the recipient cytoplasts. After artificial activation, the nuclear transfer embryos created in this manner were capable of completing several embryonic cell divisions. These procedures hold promise for enhancing the efficiency of nuclear transfer in mammals of importance for biomedical research, agriculture, biotechnology, and preserving unique, rare, and endangered species.

Biparental inheritance of gamma-tubulin during human fertilization: molecular reconstitution of functional zygotic centrosomes in inseminated human oocytes and in cell-free extracts nucleated by human sperm

Human sperm centrosome reconstitution and the parental contributions to the zygotic centrosome are examined in mammalian zygotes and after exposure of spermatozoa to Xenopus laevis cell-free extracts. The presence and inheritance of the conserved centrosomal constituents gamma-tubulin, centrin, and MPM-2 (which detects phosphorylated epitopes) are traced, as is the sperm microtubule-nucleating capability on reconstituted centrosomes. gamma-Tubulin is biparentally inherited in humans (maternal >> than paternal): Western blots detect the presence of paternal gamma-tubulin. Recruitment of maternal gamma-tubulin to the sperm centrosome occurs after sperm incorporation in vivo or exposure to cell-free extract, especially after sperm "priming" induced by disulfide bond reduction. Centrin is found in the proximal sperm centrosomal region, demonstrates expected calcium sensitivity, but appears absent from the zygotic centrosome after sperm incorporation or exposure to extracts. Sperm centrosome phosphorylation is detected after exposure of primed sperm to egg extracts as well as during the early stages of sperm incorporation after fertilization. Finally, centrosome reconstitution in cell-free extracts permits sperm aster microtubule assembly in vitro. Collectively, these results support a model of a blended zygotic centrosome composed of maternal constituents attracted to an introduced paternal template after insemination.

Effects of hormones and osmolarity in the culture medium on germinal vesicle breakdown of porcine oocytes

The present study was conducted to examine effects of hormones and osmolarity on germinal vesicle breakdown (GVBD) and histone H1 kinase (H1K) activity in porcine oocytes cultured in vitro. The basic medium used for culture of oocytes was modified Tyrode's solution in which the osmolarity was adjusted to 134 to 495 mOsm by changing the concentration of sodium chloride (NaCl). When the hormones were present, osmolarity of medium that allows GVBD of oocytes was less than 400 mOsm. However, the range of osmolarity of medium that allows meiotic maturation of oocytes was 210 to 362 mOsm. On the other hand, without hormonal supplement, the incidence of GVBD in oocytes decreased as the osmolarity of the medium increased in the rage of 210 to 362 mOsm. By increasing the osmolarity of the medium from 210 to 362 mOsm by addition with sorbitol instead of NaCl, the incidence decreased from 89.1% to 13.3%. In oocytes cultured in medium of 210 mOsm without hormones, the percentage of oocytes that underwent GVBD and had increased H1K activity 20 h after culture was significantly higher (P < 0.05) than those of oocytes cultured in the same medium supplemented with hormones or medium of 362 mOsm. These results indicate that in vitro induction of GVBD in porcine oocytes is strongly affected by osmolarity of the medium in the absence of hormones. The results also suggest that, under low osmolarity (210 mOsm), GVBD is accelerated with rapid increase of H1K activity.

Bovine oocyte cytoplasm supports development of embryos produced by nuclear transfer of somatic cell nuclei from various mammalian species

The transfer of nuclei from one cell to another provides a powerful tool for studying the interactions between the cytoplasm of one cell and the nucleus of another. This study was designed to examine the ability of the bovine metaphase oocyte cytoplasm to support mitotic cell cycles under the direction of differentiated somatic cell nuclei of various mammalian species. Skin fibroblast cells from cows, sheep, pigs, monkeys, and rats were used as sources of donor nuclei. Nuclear transfer units produced by fusion of enucleated bovine oocytes and individual fibroblasts from all species examined underwent transition to interphase accompanied by nuclear swelling, further progression through the cell cycle, and completion of the first mitosis. Regardless of the species of donor fibroblasts used, some cleaving units progressed further and developed to advanced stages, as evidenced by continuation of cell proliferation and formation of a blastocoele cavity at the time appropriate for the donor fibroblast species. Although no pregnancies have been carried to term after transfer of embryos into surrogate animals, these observations suggest that mechanisms regulating early embryonic development may be conserved among mammalian species and that bovine oocyte cytoplasm can support the introduced differentiated nucleus regardless of chromosome number, species, or age of the donor fibroblast.

Unique checkpoints during the first cell cycle of fertilization after intracytoplasmic sperm injection in rhesus monkeys

Intracytoplasmic sperm injection has begun an era of considerable improvements in treating male infertility. Despite its success, questions remain about the dangers of transmitting traits responsible for male infertility, sex and autosomal chromosome aberrations and possible mental, physical and reproductive abnormalities. We report here the first births of rhesus monkeys produced by intracytoplasmic sperm injection at rates greater or equal to those reported by clinics. Essential assumptions about this process are flawed, as shown by results with the preclinical, nonhuman primate model and with clinically discarded specimens. Dynamic imaging demonstrated the variable position of the second meiotic spindle in relation to the first polar body; consequently, microinjection targeting is imprecise and potentially lethal. Intracytoplasmic sperm injection resulted in abnormal sperm decondensation, with the unusual retention of vesicle-associated membrane protein and the perinuclear theca, and the exclusion of the nuclear mitotic apparatus from the decondensing sperm nuclear apex. Male pronuclear remodeling in the injected oocytes was required before replication of either parental genome, indicating a unique G1-to-S transition checkpoint during zygotic interphase (the first cell cycle). These irregularities indicate that the intracytoplasmic sperm injection itself might lead to the observed increased chromosome anomalies.

Fertilization and embryo development to blastocysts after intracytoplasmic sperm injection in the rhesus monkey

Notwithstanding the thousands of seemingly healthy children born after intracytoplasmic sperm injection (ICSI), it is not yet possible to conclude absolutely that the ICSI procedure might induce some altered development or that the ICSI protocol might not be improved even further. To address this in a clinically relevant system, the developmental potential of rhesus monkey embryos produced by ICSI is reported. Oocytes collected by laparoscopy from gonadotrophin-stimulated fertile females were fertilized by ICSI using spermatozoa obtained from fertile males by electro-ejaculation. Neither sperm immobilization prior to injection nor an additional chemical stimulus were necessary to achieve oocyte activation and pronuclear formation. Survival and activation of the injected oocytes were judged by the extrusion of the second polar body. Successful fertilization was confirmed by the presence of two pronuclei within 12 h post-ICSI. Some oocytes were fixed and processed for the detection of microtubules and chromatin. Fluorescent labelling revealed that by 12 h post-ICSI the male and female pronuclei were closely apposed and eccentrically positioned within a large microtubule aster. ICSI resulted in a 76.6 +/- 14.9% fertilization rate. First cleavage was completed within 24 h post-ICSI. Two-cell ICSI embryos were co-cultured in CMRL medium on a buffalo rat liver cell monolayer until the hatched blastocyst stage. Oocytes collected laparoscopically from stimulated monkeys can be fertilized by ICSI and will complete preimplantation embryo development in vitro demonstrating that the rhesus monkey is an excellent preclinical model for examining and understanding many aspects of human ICSI.

Onset of transcription in bovine oocytes and preimplantation embryos

The transition from the maternal to embryonic control of early embryonic development (MET) in mammals is not fully understood. The objective of this study was to determine the amount of transcriptional activity in immature oocytes containing germinal vesicle (GV), mature metaphase II arrested oocytes (MII), 2-, 4- and 8-cell bovine embryos by labeling with 35S-UTP followed by isolation of total RNA and autoradiography. Expression of counts per minute (CPM) per cell showed that incorporation of 35S-UTP in GV oocytes was significantly higher than the background (P < 0.01) and decreased sharply by the time the oocytes reached MII arrest. Incorporation significantly increased during the 2-cell stage and remained at the same level during the 4- and 8-cell stages. Uptake remained constant throughout different development stages (P > 0.05) with the highest variability observed during the 2-cell stage. When CPM were expressed per oocyte or embryo incorporation remained high at the GV stage, decreased to the background levels at the time of MII and increased again at the 2-cell stage. It remained at the same level during the 4-cell stage but increased significantly for the second time during the 8-cell stage. Uptake remained at the same level until the 8-cell stage when a significant increase was observed. The negative controls showed a significantly lower amount of incorporation compared to the positive control (P < 0.05). Similar results were observed by autoradiography. Our observations suggest that MET starts as early as the 2-cell stage in bovine embryos.

Timing of meiotic progression in bovine oocytes and its effect on early embryo development

This study was designed to investigate the effect of the kinetics of nuclear maturation in bovine oocytes on early embryo development and to examine whether the time of insemination of mature oocytes affects the oocytes' ability to support events of early embryo development. The time required for completion of nuclear maturation was influenced by gonadotropins used to supplement the maturation medium. Luteinizing hormone (LH) enhanced the speed of nuclear maturation when compared to follicle-stimulating hormone (FSH). Oocytes completing their nuclear maturation early (by 16 hours after the initiation of culture) were more likely to complete the first embryonic cell cycle (78% in LH vs. 43% in FSH) and develop to the blastocyst stage (47% in LH vs. 34% in FSH). As the age of the oocytes at the time of MII arrest increased (extrusion of the polar body by 20 or 24 hours), a decrease in their ability to cleave and develop to the blastocyst stage was observed. Differences in the oocyte's ability to decondense chromatin and form pronuclei were also observed. Early maturing oocytes started forming pronuclei earlier than their later maturing counterparts. The time of insemination of mature oocytes played an equally important role. Generally, when insemination of mature oocytes was delayed for 8 hours, higher proportions of fertilized oocytes developed to advanced preimplantation stages than did the oocytes inseminated immediately after metaphase II arrest.