Until now, animal cloning and the production of embryonic stem cell lines by somatic cell nuclear transfer have relied on introducing nuclei into meiotic oocytes. In contrast, attempts at somatic ...cell nuclear transfer into fertilized interphase zygotes have failed. As a result, it has generally been assumed that unfertilized human oocytes will be required for the generation of tailored human embryonic stem cell lines from patients by somatic cell nuclear transfer. Here we report, however, that, unlike interphase zygotes, mouse zygotes temporarily arrested in mitosis can support somatic cell reprogramming, the production of embryonic stem cell lines and the full-term development of cloned animals. Thus, human zygotes and perhaps human embryonic blastomeres may be useful supplements to human oocytes for the creation of patient-derived human embryonic stem cells.
Diploidy is a fundamental genetic feature in mammals, in which haploid cells normally arise only as post-meiotic germ cells that serve to ensure a diploid genome upon fertilization. Gamete ...manipulation has yielded haploid embryonic stem (ES) cells from several mammalian species, but haploid human ES cells have yet to be reported. Here we generated and analysed a collection of human parthenogenetic ES cell lines originating from haploid oocytes, leading to the successful isolation and maintenance of human ES cell lines with a normal haploid karyotype. Haploid human ES cells exhibited typical pluripotent stem cell characteristics, such as self-renewal capacity and a pluripotency-specific molecular signature. Moreover, we demonstrated the utility of these cells as a platform for loss-of-function genetic screening. Although haploid human ES cells resembled their diploid counterparts, they also displayed distinct properties including differential regulation of X chromosome inactivation and of genes involved in oxidative phosphorylation, alongside reduction in absolute gene expression levels and cell size. Surprisingly, we found that a haploid human genome is compatible not only with the undifferentiated pluripotent state, but also with differentiated somatic fates representing all three embryonic germ layers both in vitro and in vivo, despite a persistent dosage imbalance between the autosomes and X chromosome. We expect that haploid human ES cells will provide novel means for studying human functional genomics and development.
Inactivation of the β-cell transcription factor NEUROD1 causes diabetes in mice and humans. In this study, we uncovered novel functions of NEUROD1 during murine islet cell development and during the ...differentiation of human embryonic stem cells (HESCs) into insulin-producing cells. In mice, we determined that Neurod1 is required for perinatal proliferation of α- and β-cells. Surprisingly, apoptosis only makes a minor contribution to β-cell loss when
is deleted. Inactivation of
in HESCs severely impaired their differentiation from pancreatic progenitors into insulin-expressing (HESC-β) cells; however, survival or proliferation was not affected at the time points analyzed. NEUROD1 was also required in HESC-β cells for the full activation of an essential β-cell transcription factor network. These data reveal conserved and distinct functions of NEUROD1 during mouse and human β-cell development and maturation, with important implications about the function of NEUROD1 in diabetes.
Haploid human pluripotent stem cells (PSCs) integrate haploidy and pluripotency, providing a novel system for functional genomics and developmental research in humans. We have recently derived ...haploid human embryonic stem cells (ESCs) by parthenogenesis and demonstrated their wide differentiation potential and applicability for genetic screening. Because haploid cells can spontaneously become diploid, their enrichment at an early passage is key for successful derivation. In this protocol, we describe two methodologies, namely metaphase spread analysis and cell sorting, for the identification of haploid human cells within parthenogenetic ESC lines. The cell sorting approach also enables the isolation of haploid cells at low percentages, as well as the maintenance of highly enriched haploid ESC lines throughout passaging. The isolation of essentially pure populations of haploid human ESCs by this protocol requires basic PSC culture expertise and can be achieved within 4-6 weeks.
Human cleavage-stage embryos frequently acquire chromosomal aneuploidies during mitosis due to unknown mechanisms. Here, we show that S phase at the 1-cell stage shows replication fork stalling, low ...fork speed, and DNA synthesis extending into G2 phase. DNA damage foci consistent with collapsed replication forks, DSBs, and incomplete replication form in G2 in an ATR- and MRE11-dependent manner, followed by spontaneous chromosome breakage and segmental aneuploidies. Entry into mitosis with incomplete replication results in chromosome breakage, whole and segmental chromosome errors, micronucleation, chromosome fragmentation, and poor embryo quality. Sites of spontaneous chromosome breakage are concordant with sites of DNA synthesis in G2 phase, locating to gene-poor regions with long neural genes, which are transcriptionally silent at this stage of development. Thus, DNA replication stress in mammalian preimplantation embryos predisposes gene-poor regions to fragility, and in particular in the human embryo, to the formation of aneuploidies, impairing developmental potential.
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•1-cell embryos show replication fork stalling, with replication extending into G2 phase•Incompletely replicated DNA is converted to chromosome breaks and aneuploidy in mitosis•Spontaneous chromosome breaks and G2 DNA synthesis occur in congruent gene-poor regions•Chromosome fragility in human embryos occurs independently of embryonic genome activation
In human preimplantation embryos, DNA replication in G2 phase results in chromosome breakage, segmental aneuploidies, and poor embryo quality.
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