Esrrb-Cre excises loxP-flanked alleles in early four-cell embryos.

Among transgenic mice with ubiquitous Cre recombinase activity, all strains to date excise loxP-flanked (floxed) alleles either at or before the zygote stage or at nondescript stages of development. This manuscript describes a new mouse strain, in which Cre recombinase, integrated into the Esrrb locus, efficiently excises floxed alleles in pre-implantation embryos at the onset of the four-cell stage. By enabling inactivation of genes only after the embryo has undergone two cleavages, this strain should facilitate in vivo studies of genes with essential gametic or zygotic functions. In addition, this study describes a new, highly pluripotent hybrid C57BL/6J x 129S1/SvImJ mouse embryonic stem cell line, HYB12, in which this knockin and additional targeted alleles have been generated.

Gamete derivation from embryonic stem cells, induced pluripotent stem cells or somatic cell nuclear transfer-derived embryonic stem cells: state of the art.

Generating gametes from pluripotent stem cells (PSCs) has many scientific justifications and several biomedical rationales. Here, we consider several strategies for deriving gametes from PSCs from mice and primates (human and non-human) and their anticipated strengths, challenges and limitations. Although the 'Weismann barrier', which separates the mortal somatic cell lineages from the potentially immortal germline, has long existed, breakthroughs first in mice and now in humans are artificially creating germ cells from somatic cells. Spermatozoa with full reproductive viability establishing multiple generations of seemingly normal offspring have been reported in mice and, in humans, haploid spermatids with correct parent-of-origin imprints have been obtained. Similar progress with making oocytes has been published using mouse PSCs differentiated in vitro into primordial germ cells, which are then cultured after xenografting reconstructed artificial ovaries. Progress in making human oocytes artificially is proving challenging. The usefulness of these artificial gametes, from assessing environmental exposure toxicity to optimising medical treatments to prevent negative off-target effects on fertility, may prove invaluable, as may basic discoveries on the fundamental mechanisms of gametogenesis.

Stem cell therapeutic possibilities: future therapeutic options for male-factor and female-factor infertility?

Recent advances in assisted reproduction treatment have enabled some couples with severe infertility issues to conceive, but the methods are not successful in all cases. Notwithstanding the significant financial burden of assisted reproduction treatment, the emotional scars from an inability to conceive a child enacts a greater toll on affected couples. While methods have circumvented some root causes for male and female infertility, often the underlying causes cannot be treated, thus true cures for restoring a patient's fertility are limited. Furthermore, the procedures are only available if the affected patients are able to produce gametes. Patients rendered sterile by medical interventions, exposure to toxicants or genetic causes are unable to utilize assisted reproduction to conceive a child - and often resort to donors, where permitted. Stem cells represent a future potential avenue for allowing these sterile patients to produce offspring. Advances in stem cell biology indicate that stem cell replacement therapies or in-vitro differentiation may be on the horizon to treat and could cure male and female infertility, although significant challenges need to be met before this technology can reach clinical practice. This article discusses these advances and describes the impact that these advances may have on treating infertility.

Blastocyst development after fertilization with in vitro spermatids derived from nonhuman primate embryonic stem cells.

OBJECTIVE: To demonstrate that functional spermatids can be derived in vitro from nonhuman primate pluripotent stem cells. DESIGN: Green fluorescent protein-labeled, rhesus macaque nonhuman primate embryonic stem cells (nhpESCs) were differentiated into advanced male germ cell lineages using a modified serum-free spermatogonial stem cell culture medium. In vitro-derived round spermatid-like cells (rSLCs) from differentiated nhpESCs were assessed for their ability to fertilize rhesus oocytes by intracytoplasmic sperm(atid) injection. SETTING: Multiple academic laboratory settings. PATIENTS: Not applicable. INTERVENTIONS: Intracytoplasmic sperm(atid) injection of in vitro-derived spermatids from nhpESCs into rhesus macaque oocytes. MAIN OUTCOME MEASURES: Differentiation into spermatogenic cell lineages was measured through multiple assessments including ribonucleic acid sequencing and immunocytochemistry for various spermatogenic markers. In vitro spermatids were assessed for their ability to fertilize oocytes by intracytoplasmic sperm(atid) injection by assessing early fertilization events such as spermatid deoxyribonucleic acid decondensation and pronucleus formation/apposition. Preimplantation embryo development from the one-cell zygote stage to the blastocyst stage was also assessed. RESULTS: Nonhuman primate embryonic stem cells can be differentiated into advanced germ cell lineages, including haploid rSLCs. These rSLCs undergo deoxyribonucleic acid decondensation and pronucleus formation/apposition when microinjected into rhesus macaque mature oocytes, which, after artificial activation and coinjection of ten-eleven translocation 3 protein, undergo embryonic divisions with approximately 12% developing successfully into expanded blastocysts. CONCLUSIONS: This work demonstrates that rSLCs, generated in vitro from primate pluripotent stem cells, mimic many of the capabilities of in vivo round spermatids and perform events essential for preimplantation development. To our knowledge, this work represents, for the first time, that functional spermatid-like cells can be derived in vitro from primate pluripotent stem cells.

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.

Pedigreed primate embryonic stem cells express homogeneous familial gene profiles.

Human embryonic stem cells (hESCs) hold great biomedical promise, but experiments comparing them produce heterogeneous results, raising concerns regarding their reliability and utility, although these variations may result from their disparate and anonymous origins. To determine whether primate ESCs have intrinsic biological limitations compared with mouse ESCs, we examined expression profiles and pluripotency of newly established nonhuman primate ESC (nhpESCs). Ten pedigreed nhpESC lines, seven full siblings (fraternal quadruplets and fraternal triplets), and nine half siblings were derived from 41 rhesus embryos; derivation success correlated with embryo quality. Each line has been growing continuously for approximately 1 year with stable diploid karyotype (except for one stable trisomy) and expresses in vitro pluripotency markers, and eight have already formed teratomas. Unlike the heterogeneous gene expression profiles found among hESCs, these nhpESCs display remarkably homogeneous profiles (>97%), with full-sibling lines nearly identical (>98.2%). Female nhpESCs express genes distinct from their brother lines; these sensitive analyses are enabled because of the very low background differences. Experimental comparisons among these primate ESCs may prove more reliable than currently available hESCs, since they are akin to inbred mouse strains in which genetic variables are also nearly eliminated. Finally, contrasting the biological similarities among these lines with the heterogeneous hESCs might suggest that additional, more uniform hESC lines are justified. Taken together, pedigreed primate ESCs display homogeneous and reliable expression profiles. These similarities to mouse ESCs suggest that heterogeneities found among hESCs likely result from their disparate origins rather than intrinsic biological limitations with primate embryonic stem cells.

Central Spindle Self-Organization and Cytokinesis in Artificially Activated Sea Urchin Eggs.

The ability of microtubules of the mitotic apparatus to control the positioning and initiation of the cleavage furrow during cytokinesis was first established from studies on early echinoderm embryos. However, the identity of the microtubule population that imparts cytokinetic signaling is unclear. The two main--and not necessarily mutually exclusive--candidates are the central spindle and the astral rays. In the present study, we examined cytokinesis in ammonia-activated sea urchin eggs, which lack paternally derived centrosomes and undergo mitosis mediated by unusual anastral, bipolar mini-spindles. Live cell imaging and immunolabeling for microtubules and the centralspindlin constituent and kinesin-related protein, MKLP1, demonstrated that furrowing in ammonia-activated eggs was associated with aligned arrays of centralspindlin-linked, opposed bundles of antiparallel microtubules. These autonomous, zipper-like arrays were not associated with a mitotic apparatus, but did possess characteristics similar to the central spindle region of control, fertilized embryos. Our results highlight the self-organizing nature of the central spindle region and its ability to induce cytokinesis-like furrowing, even in the absence of a complete mitotic apparatus.

The expression of mitochondrial DNA transcription factors during early cardiomyocyte in vitro differentiation from human embryonic stem cells.

Mitochondrial biogenesis and activation of both oxidative phosphorylation, as well as transcription and replication of the mitochondrial genome, are key regulatory events in cell differentiation. Mitochondrial DNA transcription and replication are highly dependent on the interaction with nuclear-encoded transcription factors translocated from the nucleus. Using a human embryonic stem cell line, HSF 6, we analyzed the proliferation of mitochondria and the expression of mtDNA-specific transcription factors in undifferentiated, migratory embryonic stem cells and spontaneously derived cardiomyocytes. Mitochondrial proliferation and mtDNA transcription are initiated in human embryonic stem cells as they undergo spontaneous differentiation in culture into beating cardiomyocytes. Undifferentiated, pluripotent human embryonic stem cells have few mitochondria, and, as they differentiate, they polarize to one extremity of the cell and then bipolarize the differentiating cell. The differentiated cell then adopts the cytoplasmic configuration of a somatic cell as evidenced in differentiating cardiomyocytes. Transcription and replication of the extranuclear mitochondrial genome is dependent on nuclear encoded factors exported to the mitochondrion. However, the differentiating cardiomyocytes have reduced or absent levels of these transcription and replication factors, namely mitochondrial transcription factors A, B1, B2, and nuclear respiratory factor 1 and polymerase gamma. Therefore, final embryonic stem cell commitment may be influenced by mitochondrial proliferation and mtDNA transcription. However, it is likely that differentiating cardiomyocytes are in mitochondrial arrest, awaiting commitment to a final cell fate.

Fate of sperm components during assisted reproduction: implications for infertility.

Studies in non-human primates highlight their suitability as preclinical models for investigating assisted reproduction techniques. The cytoskeletal events of fertilization in non-human primates are similar to those in humans in that they require a paternally derived centrosome. The centrosome, introduced by the sperm at fertilization, organizes a microtubule array that is responsible for bringing the parental genomes together at first mitosis. Incomplete functioning of the sperm centrosome during fertilization has been identified as a novel form of infertility that would not necessarily benefit from intracytoplasmic sperm injection (ICSI). The global use of ICSI to overcome male infertility has been very successful, although concerns remain regarding the long-term effects on children born after ICSI. The cytoskeletal events that occur during ICSI are quite different from the events of in vitro fertilization: a sperm selected for ICSI does not undergo typical oocyte interactions, and abnormal remodelling of the male pronucleus may result. The implications of these findings are discussed in relation to the safety of the ICSI technique.

Adult somatic cells to the rescue: nuclear reprogramming and the dispensability of gonadal germ cells.

With advances in cancer therapies, survival rates in prepubescent patients have steadily increased. However, a number of these surviving patients have been rendered sterile owing to their rigorous oncologic treatment regimens. In addition to cancer treatments, men and women, who are genetically fertile, can become infertile owing to immune suppression treatments, exposure to environmental and industrial toxicants, and injury. Notwithstanding the great emotional burden from an inability to conceive a child with their partner, the financial burdens for testing and treatment are high, and successful treatment of these patients' sterility is rare. Recent advances in pluripotent stem cell differentiation and the generation of patient-specific, induced pluripotent stem cells indicate that stem cell replacement therapies or in vitro differentiation followed by IVF may be on the horizon. Here we discuss these recent advances, their relevance to treating male-factor and female-factor infertility, and what experimental procedures must be carried out in animal models before these exciting new treatments can be used in a clinical setting. The goal of this research is to generate functional gametes from no greater starting material than a mere skin biopsy.

Ex vivo reconstitution of arterial endothelium by embryonic stem cell-derived endothelial progenitor cells in baboons.

There is an increasing need for an animal model that can be used to translate basic research into clinical therapy. We documented the differentiation and functional competence of embryonic stem cell (ESC)-derived endothelial cells in baboons. Baboon angioblasts were sequentially differentiated from embryoid body cultures for 9 days in an angioblast differentiation medium with varying concentrations of BMP-4, FLT-3 ligand, stem cell factor, thrombopoietin, basic fibroblast growth factor (FGF), vascular endothelial growth factor (VEGF), and knockout serum replacement. Real-time polymerase chain reaction results showed that ESC-derived angioblasts downregulated NANOG and OCT3/4, upregulated T-brachyury and GATA2, and moderately expressed CD34; they did not express CD144, TEK, or VWF, and varied in levels of CD31 expression. Several populations of putative angioblasts appeared 3 days and 9 days after differentiation, as identified by flow cytometry. Angioblasts at this stage exhibited dual paths of differentiation toward hematopoietic and vascular fates. To examine whether derived angioblasts could reconstitute the endothelium, we built an ex vivo culture system and seeded fluorescently labeled angioblast cultures onto a denuded segment of the femoral artery. We found that the seeded cells were able to grow into the endothelium on the interior surface of denuded artery segments within 5 days after seeding. After 14 days of ex vivo culture, the transplanted cells expressed CD31, an endothelial marker. The control arteries, seeded with vehicle only, did not harbor cells with endothelial markers. We conclude that ESC-derived angioblasts are promising therapeutic agents for repairing damaged vasculature, and that the baboon model will be vital for optimizing therapies for human clinical studies.

Direct differentiation of human pluripotent stem cells into haploid spermatogenic cells.

Human embryonic stem cells (hESCs) and induced pluripotent stem cells (hiPSCs) have been shown to differentiate into primordial germ cells (PGCs) but not into spermatogonia, haploid spermatocytes, or spermatids. Here, we show that hESCs and hiPSCs differentiate directly into advanced male germ cell lineages, including postmeiotic, spermatid-like cells, in vitro without genetic manipulation. Furthermore, our procedure mirrors spermatogenesis in vivo by differentiating PSCs into UTF1-, PLZF-, and CDH1-positive spermatogonia-like cells; HIWI- and HILI-positive spermatocyte-like cells; and haploid cells expressing acrosin, transition protein 1, and protamine 1 (proteins that are uniquely found in spermatids and/or sperm). These spermatids show uniparental genomic imprints similar to those of human sperm on two loci: H19 and IGF2. These results demonstrate that male PSCs have the ability to differentiate directly into advanced germ cell lineages and may represent a novel strategy for studying spermatogenesis in vitro.

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.

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.

Freeze-dried primate sperm retains early reproductive potential after intracytoplasmic sperm injection.

Oocytes inseminated by intracytoplasmic sperm injection using fresh ejaculated or freeze-dried rhesus macaque sperm showed similar activation, sperm aster assembly, and male-female pronuclear apposition rates.

Bipolar, anastral spindle development in artificially activated sea urchin eggs.

The mitotic apparatus of the early sea urchin embryo is the archetype example of a centrosome-dominated, large aster spindle organized by means of the centriole of the fertilizing sperm. In this study, we tested the hypothesis that artificially activated sea urchin eggs possess the capacity to assemble the anastral, bipolar spindles present in many acentrosomal systems. Control fertilized Lytechinus pictus embryos and ammonia-activated eggs were immunolabeled for tubulin, centrosomal material, the spindle pole structuring protein NuMA and the mitotic kinesins MKLP1/Kinesin-6, Eg5/Kinesin-5, and KinI/Kinesin-13. Confocal imaging showed that a subset of ammonia-activated eggs contained bipolar "mini-spindles" that were anastral; displayed metaphase and anaphase-like stages; labeled for centrosomal material, NuMA, and the three mitotic kinesins; and were observed in living eggs using polarization optics. These results suggest that spindle structural and motor proteins have the ability to organize bipolar, anastral spindles in sea urchin eggs activated in the absence of the paternal centriole.