RESUMEN
Most human embryos are aneuploid. Aneuploidy frequently arises during the early mitotic divisions of the embryo, but its origin remains elusive. Human zygotes that cluster their nucleoli at the pronuclear interface are thought to be more likely to develop into healthy euploid embryos. Here, we show that the parental genomes cluster with nucleoli in each pronucleus within human and bovine zygotes, and clustering is required for the reliable unification of the parental genomes after fertilization. During migration of intact pronuclei, the parental genomes polarize toward each other in a process driven by centrosomes, dynein, microtubules, and nuclear pore complexes. The maternal and paternal chromosomes eventually cluster at the pronuclear interface, in direct proximity to each other, yet separated. Parental genome clustering ensures the rapid unification of the parental genomes on nuclear envelope breakdown. However, clustering often fails, leading to chromosome segregation errors and micronuclei, incompatible with healthy embryo development.
Asunto(s)
Embrión de Mamíferos/metabolismo , Desarrollo Embrionario/genética , Aneuploidia , Animales , Bovinos , Nucléolo Celular/metabolismo , Núcleo Celular/metabolismo , Centrosoma/metabolismo , Segregación Cromosómica/fisiología , Cromosomas/metabolismo , Fertilización/genética , Humanos , Masculino , Microtúbulos/metabolismo , Mitosis , Oocitos/metabolismo , Espermatozoides/metabolismo , Cigoto/metabolismoRESUMEN
Our understanding of the molecular events driving cell specification in early mammalian development relies mainly on mouse studies, and it remains unclear whether these mechanisms are conserved across mammals, including humans. We have shown that the establishment of cell polarity via aPKC is a conserved event in the initiation of the trophectoderm (TE) placental programme in mouse, cow and human embryos. However, the mechanisms transducing cell polarity into cell fate in cow and human embryos are unknown. Here, we have examined the evolutionary conservation of Hippo signalling, which is thought to function downstream of aPKC activity, in four different mammalian species: mouse, rat, cow and human. In all four species, inhibition of the Hippo pathway by targeting LATS kinases is sufficient to drive ectopic TE initiation and downregulation of SOX2. However, the timing and localisation of molecular markers differ across species, with rat embryos more closely recapitulating human and cow developmental dynamics, compared with the mouse. Our comparative embryology approach uncovered intriguing differences as well as similarities in a fundamental developmental process among mammals, reinforcing the importance of cross-species investigations.
Asunto(s)
Vía de Señalización Hippo , Transducción de Señal , Bovinos , Humanos , Femenino , Embarazo , Ratones , Ratas , Animales , Transducción de Señal/fisiología , Proteínas Serina-Treonina Quinasas/genética , Proteínas Serina-Treonina Quinasas/metabolismo , Blastocisto/metabolismo , Placenta/metabolismo , Mamíferos/metabolismo , Linaje de la CélulaRESUMEN
Current understandings of cell specification in early mammalian pre-implantation development are based mainly on mouse studies. The first lineage differentiation event occurs at the morula stage, with outer cells initiating a trophectoderm (TE) placental progenitor program. The inner cell mass arises from inner cells during subsequent developmental stages and comprises precursor cells of the embryo proper and yolk sac1. Recent gene-expression analyses suggest that the mechanisms that regulate early lineage specification in the mouse may differ in other mammals, including human2-5 and cow6. Here we show the evolutionary conservation of a molecular cascade that initiates TE segregation in human, cow and mouse embryos. At the morula stage, outer cells acquire an apical-basal cell polarity, with expression of atypical protein kinase C (aPKC) at the contact-free domain, nuclear expression of Hippo signalling pathway effectors and restricted expression of TE-associated factors such as GATA3, which suggests initiation of a TE program. Furthermore, we demonstrate that inhibition of aPKC by small-molecule pharmacological modulation or Trim-Away protein depletion impairs TE initiation at the morula stage. Our comparative embryology analysis provides insights into early lineage specification and suggests that a similar mechanism initiates a TE program in human, cow and mouse embryos.
Asunto(s)
Evolución Biológica , Ectodermo/metabolismo , Embrión de Mamíferos/citología , Embrión de Mamíferos/metabolismo , Regulación del Desarrollo de la Expresión Génica , Transcripción Genética , Trofoblastos/metabolismo , Proteínas Adaptadoras Transductoras de Señales/metabolismo , Animales , Masa Celular Interna del Blastocisto/citología , Masa Celular Interna del Blastocisto/metabolismo , Bovinos , Linaje de la Célula , Polaridad Celular , Ectodermo/citología , Embrión de Mamíferos/enzimología , Femenino , Factor de Transcripción GATA3/metabolismo , Vía de Señalización Hippo , Humanos , Ratones , Mórula/citología , Mórula/enzimología , Mórula/metabolismo , Placenta/citología , Placenta/metabolismo , Embarazo , Proteína Quinasa C/metabolismo , Proteínas Serina-Treonina Quinasas/metabolismo , Factores de Transcripción SOXB1/metabolismo , Transducción de Señal , Factores de Transcripción/metabolismo , Trofoblastos/citología , Proteínas Señalizadoras YAP , Saco Vitelino/citología , Saco Vitelino/metabolismoRESUMEN
Current knowledge of the transcriptional regulation of human pluripotency is incomplete, with lack of interspecies conservation observed. Single-cell transcriptomics analysis of human embryos previously enabled us to identify transcription factors, including the zinc-finger protein KLF17, that are enriched in the human epiblast and naïve human embryonic stem cells (hESCs). Here, we show that KLF17 is expressed coincident with the known pluripotency-associated factors NANOG and SOX2 across human blastocyst development. We investigate the function of KLF17 using primed and naïve hESCs for gain- and loss-of-function analyses. We find that ectopic expression of KLF17 in primed hESCs is sufficient to induce a naïve-like transcriptome and that KLF17 can drive transgene-mediated resetting to naïve pluripotency. This implies a role for KLF17 in establishing naïve pluripotency. However, CRISPR-Cas9-mediated knockout studies reveal that KLF17 is not required for naïve pluripotency acquisition in vitro. Transcriptome analysis of naïve hESCs identifies subtle effects on metabolism and signalling pathways following KLF17 loss of function, and possible redundancy with other KLF paralogues. Overall, we show that KLF17 is sufficient, but not necessary, for naïve pluripotency under the given in vitro conditions.
Asunto(s)
Blastocisto/metabolismo , Regulación del Desarrollo de la Expresión Génica , Estratos Germinativos/metabolismo , Células Madre Embrionarias Humanas/metabolismo , Factores de Transcripción/metabolismo , Humanos , Proteína Homeótica Nanog/genética , Proteína Homeótica Nanog/metabolismo , Factores de Transcripción SOXB1/genética , Factores de Transcripción SOXB1/metabolismo , Factores de Transcripción/genéticaRESUMEN
Despite their fundamental biological and clinical importance, the molecular mechanisms that regulate the first cell fate decisions in the human embryo are not well understood. Here we use CRISPR-Cas9-mediated genome editing to investigate the function of the pluripotency transcription factor OCT4 during human embryogenesis. We identified an efficient OCT4-targeting guide RNA using an inducible human embryonic stem cell-based system and microinjection of mouse zygotes. Using these refined methods, we efficiently and specifically targeted the gene encoding OCT4 (POU5F1) in diploid human zygotes and found that blastocyst development was compromised. Transcriptomics analysis revealed that, in POU5F1-null cells, gene expression was downregulated not only for extra-embryonic trophectoderm genes, such as CDX2, but also for regulators of the pluripotent epiblast, including NANOG. By contrast, Pou5f1-null mouse embryos maintained the expression of orthologous genes, and blastocyst development was established, but maintenance was compromised. We conclude that CRISPR-Cas9-mediated genome editing is a powerful method for investigating gene function in the context of human development.
Asunto(s)
Desarrollo Embrionario/genética , Edición Génica , Regulación del Desarrollo de la Expresión Génica , Factor 3 de Transcripción de Unión a Octámeros/genética , Factor 3 de Transcripción de Unión a Octámeros/metabolismo , Animales , Blastocisto/metabolismo , Sistemas CRISPR-Cas/genética , Linaje de la Célula , Ectodermo/metabolismo , Embrión de Mamíferos/citología , Embrión de Mamíferos/embriología , Embrión de Mamíferos/metabolismo , Femenino , Estratos Germinativos/metabolismo , Células Madre Embrionarias Humanas/citología , Células Madre Embrionarias Humanas/metabolismo , Humanos , Masculino , Ratones , Proteína Homeótica Nanog/genética , Proteína Homeótica Nanog/metabolismo , Factor 3 de Transcripción de Unión a Octámeros/deficiencia , Especificidad por Sustrato , Cigoto/metabolismoRESUMEN
This corrects the article DOI: 10.1038/nature24033.
RESUMEN
Assisted reproductive technology is today considered a safe and reliable medical intervention, with healthy live births a reality for many IVF and ICSI treatment cycles. However, there are increasing numbers of published reports describing epigenetic/imprinting anomalies in children born as a result of these procedures. These anomalies have been attributed to methylation errors in embryo chromatin remodelling during in vitro culture. Here we re-visit three concepts: (1) the so-called 'in vitro toxicity' of 'essential amino acids' before the maternal to zygotic transition period; (2) the effect of hyperstimulation (controlled ovarian hyperstimulation) on homocysteine in the oocyte environment and the effect on methylation in the absence of essential amino acids; and (3) the fact/postulate that during the early stages of development the embryo undergoes a 'global' demethylation. Methylation processes require efficient protection against oxidative stress, which jeopardizes the correct acquisition of methylation marks as well as subsequent methylation maintenance. The universal precursor of methylation [by S-adenosyl methionine (SAM)], methionine, 'an essential amino acid', should be present in the culture. Polyamines, regulators of methylation, require SAM and arginine for their syntheses. Cystine, another 'semi-essential amino acid', is the precursor of the universal protective antioxidant molecule: glutathione. It protects methylation marks against some undue DNA demethylation processes through ten-eleven translocation (TET), after formation of hydroxymethyl cytosine. Early embryos are unable to convert homocysteine to cysteine as the cystathionine ß-synthase pathway is not active. In this way, cysteine is a 'real essential amino acid'. Most IVF culture medium do not maintain methylation/epigenetic processes, even in mouse assays. Essential amino acids should be present in human IVF medium to maintain adequate epigenetic marking in preimplantation embryos. Furthermore, morphological and morphometric data need to be re-evaluated, taking into account the basic biochemical processes involved in early life.
Asunto(s)
Metilación de ADN , Fertilización In Vitro , Animales , Blastocisto , Epigénesis Genética , Fertilización In Vitro/métodos , Homeostasis , Ratones , Estrés Oxidativo , Técnicas Reproductivas AsistidasRESUMEN
Medically assisted reproduction, now considered a routine, successful treatment for infertility worldwide, has produced at least 8 million live births. However, a growing body of evidence is pointing toward an increased incidence of epigenetic/imprinting disorders in the offspring, raising concern that the techniques involved may have an impact on crucial stages of early embryo and fetal development highly vulnerable to epigenetic influence. In this paper, the key role of methylation processes in epigenesis, namely the essential biochemical/metabolic pathways involving folates and one-carbon cycles necessary for correct DNA/histone methylation, is discussed. Furthermore, potential contributors to epigenetics dysregulation during the three phases of assisted reproduction: preparation for and controlled ovarian hyperstimulation (COH); methylation processes during the preimplantation embryo culture stages; the effects of unmetabolized folic acid (UMFA) during embryogenesis on imprinting methyl "tags", are described. Advances in technology have opened a window into developmental processes that were previously inaccessible to research: it is now clear that ART procedures have the potential to influence DNA methylation in embryonic and fetal life, with an impact on health and disease risk in future generations. Critical re-evaluation of protocols and procedures is now an urgent priority, with a focus on interventions targeted toward improving ART procedures, with special attention to in vitro culture protocols and the effects of excessive folic acid intake.
Asunto(s)
Impresión Genómica , Técnicas Reproductivas Asistidas , Metilación de ADN , Epigénesis Genética , Ácido Fólico , Reproducción , Técnicas Reproductivas Asistidas/efectos adversosRESUMEN
Methylation is a universal biochemical process which covalently adds methyl groups to a variety of molecular targets. It plays a critical role in two major global regulatory mechanisms, epigenetic modifications and imprinting, via methyl tagging on histones and DNA. During reproduction, the two genomes that unite to create a new individual are complementary but not equivalent. Methylation determines the complementary regulatory characteristics of male and female genomes. DNA methylation is executed by methyltransferases that transfer a methyl group from S-adenosylmethionine, the universal methyl donor, to cytosine residues of CG (also designated CpG). Histones are methylated mainly on lysine and arginine residues. The methylation processes regulate the main steps in reproductive physiology: gametogenesis, and early and late embryo development. A focus will be made on the impact of assisted reproductive technology and on the impact of endocrine disruptors (EDCs) via generation of oxidative stress.
Asunto(s)
Metilación de ADN , Epigénesis Genética , Código de Histonas , Animales , Desarrollo Embrionario/genética , Gametogénesis , Humanos , Técnicas Reproductivas Asistidas/efectos adversosRESUMEN
Life expectancy has increased since World War II, and this may be attributed to several aspects of modern lifestyles. However, now we are faced with a downturn, which seems to be the result of environmental issues. This paradigm is paralleled with reduced human fertility, decreased sperm quality, increased premature ovarian failure, and diminished ovarian reserve syndromes. Endocrine disruptor chemicals and other toxic chemicals, herbicides, pesticides, plasticizers, to mention a few, are a rising concern in today's environment. Some of these are commonly used in the domestic setting: cleaning material and cosmetics and they have a known impact on epigenesis and imprinting via perturbation of methylation processes. Pollution from polyaromatic hydrocarbons, particulate matter <10 and <2.5 µm, and ozone released into the air, all affect fertility. Poor food processing management is a source of DNA adduct formation, which impairs the quality of gametes. An important concern is the nanoparticles that are present in food and are thought to induce oxidative stress. Now is the time to take a step backward. Global management of the environment and food production is required urgently to protect the fertility of future generations.
Asunto(s)
Metilación de ADN/efectos de los fármacos , Desarrollo Embrionario/efectos de los fármacos , Disruptores Endocrinos/efectos adversos , Contaminantes Ambientales/efectos adversos , Epigénesis Genética/efectos de los fármacos , Animales , Femenino , Inocuidad de los Alimentos , Células Germinativas/efectos de los fármacos , Humanos , Infertilidad/inducido químicamente , Masculino , Ratones , Nanopartículas , Estrés Oxidativo/efectos de los fármacos , Residuos de PlaguicidasRESUMEN
Here, we provide fundamental insights into early human development by single-cell RNA-sequencing of human and mouse preimplantation embryos. We elucidate conserved transcriptional programs along with those that are human specific. Importantly, we validate our RNA-sequencing findings at the protein level, which further reveals differences in human and mouse embryo gene expression. For example, we identify several genes exclusively expressed in the human pluripotent epiblast, including the transcription factor KLF17. Key components of the TGF-ß signalling pathway, including NODAL, GDF3, TGFBR1/ALK5, LEFTY1, SMAD2, SMAD4 and TDGF1, are also enriched in the human epiblast. Intriguingly, inhibition of TGF-ß signalling abrogates NANOG expression in human epiblast cells, consistent with a requirement for this pathway in pluripotency. Although the key trophectoderm factors Id2, Elf5 and Eomes are exclusively localized to this lineage in the mouse, the human orthologues are either absent or expressed in alternative lineages. Importantly, we also identify genes with conserved expression dynamics, including Foxa2/FOXA2, which we show is restricted to the primitive endoderm in both human and mouse embryos. Comparison of the human epiblast to existing embryonic stem cells (hESCs) reveals conservation of pluripotency but also additional pathways more enriched in hESCs. Our analysis highlights significant differences in human preimplantation development compared with mouse and provides a molecular blueprint to understand human embryogenesis and its relationship to stem cells.
Asunto(s)
Blastocisto/citología , Linaje de la Célula/fisiología , Regulación del Desarrollo de la Expresión Génica/fisiología , Análisis de Secuencia de ARN/métodos , Análisis de la Célula Individual/métodos , Animales , Perfilación de la Expresión Génica , Regulación del Desarrollo de la Expresión Génica/genética , Humanos , Ratones , Análisis de Componente Principal , Especificidad de la EspecieRESUMEN
There were errors published in Development 142, 3151-3165.In the issue published online on 22 September 2015, Fig. 3 was mislabelled: panels A, B, C and D should have been B, C, D and A, respectively. In the legend, the text prior to '(A) Cytoscape enrichment map ' should not have been included. The correct version of the figure and legend now appear online and in print.We apologise to the authors and readers for this mistake.
RESUMEN
PURPOSE: Gametocyte-specific factor 1 has been shown in other species to be required for the silencing of retrotransposons via the Piwi-interacting RNA (piRNA) pathway. In this study, we aimed to isolate and assess expression of transcripts of the gametocyte-specific factor 1 (GTSF1) gene in the human female germline and in preimplantation embryos. METHODS: Complementary DNA (cDNA) libraries from human fetal ovaries and testes, human oocytes and preimplantation embryos and ovarian follicles isolated from an adult ovarian cortex biopsy were used to as templates for PCR, cloning and sequencing, and real time PCR experiments of GTSF1 expression. RESULTS: GTSF1 cDNA clones that covered the entire coding region were isolated from human oocytes and preimplantation embryos. GTSF1 mRNA expression was detected in archived cDNAs from staged human ovarian follicles, germinal vesicle (GV) stage oocytes, metaphase II oocytes, and morula and blastocyst stage preimplantation embryos. Within the adult female germline, expression was highest in GV oocytes. GTSF1 mRNA expression was also assessed in human fetal ovary and was observed to increase during gestation, from 8 to 21 weeks, during which time oogonia enter meiosis and primordial follicle formation first occurs. In human fetal testis, GTSF1 expression also increased from 8 to 19 weeks. CONCLUSIONS: To our knowledge, this report is the first to describe the expression of the human GTSF1 gene in human gametes and preimplantation embryos.
Asunto(s)
Desarrollo Embrionario/genética , Células Germinativas , Meiosis/genética , Proteínas/genética , Adulto , Blastocisto/metabolismo , ADN Complementario , Femenino , Feto , Regulación del Desarrollo de la Expresión Génica , Humanos , Péptidos y Proteínas de Señalización Intracelular , Oocitos/crecimiento & desarrollo , Oocitos/metabolismo , Folículo Ovárico/crecimiento & desarrollo , Folículo Ovárico/metabolismo , Proteínas/metabolismoRESUMEN
The negative effect of oxidative stress on the human reproductive process is no longer a matter for debate. Oxidative stress affects female and male gametes and the developmental capacity of embryos. Its effect can continue through late stages of pregnancy. Metabolic disorders and psychiatric problems can also be caued by DNA methylation and epigenetic errors. Age has a negative effect on oxidative stress and DNA methylation, and recent observations suggest that older men are at risk of transmitting epigenetic disorders to their offspring. Environmental endocrine disruptors can also increase oxidative stress and methylation errors. Oxidative stress and DNA methylation feature a common denominator: the one carbon cycle. This important metabolic pathway stimulates glutathione synthesis and recycles homocysteine, a molecule that interferes with the process of methylation. Glutathione plays a pivotal role during oocyte activation, protecting against reactive oxygen species. Assisted reproductive techniques may exacerbate defects in methylation and epigenesis. Antioxidant supplements are proposed to reduce the risk of potentially harmful effects, but their use has failed to prevent problems and may sometimes be detrimental. New concepts reveal a significant correlation between oxidative stress, methylation processes and epigenesis, and have led to changes in media composition with positive preliminary clinical consequences.
Asunto(s)
Metilación de ADN , Estrés Oxidativo , Reproducción/fisiología , Animales , Antioxidantes/química , Blastocisto , Endometriosis/fisiopatología , Epigénesis Genética , Femenino , Fertilidad , Radicales Libres/química , Humanos , Infertilidad Masculina/fisiopatología , Masculino , Enfermedades Metabólicas/fisiopatología , Ratones , Oocitos/citología , Oocitos/metabolismo , Ovario/metabolismo , Síndrome del Ovario Poliquístico/fisiopatología , Embarazo , Especies Reactivas de Oxígeno/metabolismo , Técnicas Reproductivas Asistidas , Riesgo , Espermatozoides/metabolismoRESUMEN
The oviduct has long been considered a 'pipeline', a tube allowing transit of spermatozoa and embryos; this perspective has been reinforced by the success of human IVF. Evidence accumulated over several decades, however, indicates that embryos can modulate the metabolism of tubal cells in their environment. Human IVF culture media is based on formulations that pass mouse embryo assays as quality control: the requirements of mouse embryos differ from those of human embryos, and therefore conditions for human IVF are far removed from the natural environment of the oviduct. The preimplantation environment, both in vitro and in vivo, is known to affect the health of offspring through mechanisms that influence imprinting. Recent studies also show that male accessory glands act in synergy with the oviduct in providing an optimal environment, and this represents a further perspective on the oviduct's contribution to harmonious embryo development and subsequent long-term health. The metabolism of the human embryo is far from being understood, and a 'return' to in-vivo conditions for preimplantation development is worthy of consideration. Although results obtained in rodents must be interpreted with caution, lessons learned from animal embryo culture must not be neglected.
Asunto(s)
Ectogénesis , Técnicas de Cultivo de Embriones/métodos , Transferencia de Embrión/efectos adversos , Trompas Uterinas/fisiología , Infertilidad Femenina/terapia , Modelos Biológicos , Semen/fisiología , Animales , Células Cultivadas , Técnicas de Cocultivo , Desarrollo Embrionario , Trompas Uterinas/citología , Trompas Uterinas/metabolismo , Trompas Uterinas/fisiopatología , Femenino , Fertilización In Vitro/efectos adversos , Transferencia Intrafalopiana del Gameto/efectos adversos , Humanos , Infertilidad Femenina/metabolismo , Infertilidad Femenina/fisiopatología , Masculino , Embarazo , Transferencia Intrafalopiana del Cigoto/efectos adversosAsunto(s)
Blastocisto/metabolismo , Ensamble y Desensamble de Cromatina , Cromatina/efectos de los fármacos , Medios de Cultivo/farmacología , Metilación de ADN , Técnicas de Cultivo de Embriones , Técnicas Reproductivas Asistidas , Aminoácidos/metabolismo , Aminoácidos/farmacología , Blastocisto/efectos de los fármacos , Ensamble y Desensamble de Cromatina/efectos de los fármacos , Anomalías Congénitas/etiología , Anomalías Congénitas/prevención & control , Reparación del ADN , Desarrollo Embrionario/efectos de los fármacos , Disruptores Endocrinos/toxicidad , Femenino , Impresión Genómica , Glucosa/metabolismo , Glucosa/farmacología , Humanos , Recién Nacido , Metionina/administración & dosificación , Metionina/toxicidad , Metilación , Metilenotetrahidrofolato Reductasa (NADPH2)/genética , Oocitos/efectos de los fármacos , Oocitos/metabolismo , Estrés Oxidativo , Embarazo , Técnicas Reproductivas Asistidas/efectos adversos , S-Adenosilmetionina/metabolismoRESUMEN
Recent advances in single-cell omics have transformed characterisation of cell types in challenging-to-study biological contexts. In contexts with limited single-cell samples, such as the early human embryo inference of transcription factor-gene regulatory network (GRN) interactions is especially difficult. Here, we assessed application of different linear or non-linear GRN predictions to single-cell simulated and human embryo transcriptome datasets. We also compared how expression normalisation impacts on GRN predictions, finding that transcripts per million reads outperformed alternative methods. GRN inferences were more reproducible using a non-linear method based on mutual information (MI) applied to single-cell transcriptome datasets refined with chromatin accessibility (CA) (called MICA), compared with alternative network prediction methods tested. MICA captures complex non-monotonic dependencies and feedback loops. Using MICA, we generated the first GRN inferences in early human development. MICA predicted co-localisation of the AP-1 transcription factor subunit proto-oncogene JUND and the TFAP2C transcription factor AP-2γ in early human embryos. Overall, our comparative analysis of GRN prediction methods defines a pipeline that can be applied to single-cell multi-omics datasets in especially challenging contexts to infer interactions between transcription factor expression and target gene regulation.
Asunto(s)
Redes Reguladoras de Genes , Multiómica , Humanos , Redes Reguladoras de Genes/genética , Factores de Transcripción/metabolismo , Transcriptoma/genética , Embrión de MamíferosRESUMEN
Development requires coordinated interactions between the epiblast, which generates the embryo proper; the trophectoderm, which generates the placenta; and the hypoblast, which forms both the anterior signalling centre and the yolk sac. These interactions remain poorly understood in human embryogenesis because mechanistic studies have only recently become possible. Here we examine signalling interactions post-implantation using human embryos and stem cell models of the epiblast and hypoblast. We find anterior hypoblast specification is NODAL dependent, as in the mouse. However, while BMP inhibits anterior signalling centre specification in the mouse, it is essential for its maintenance in human. We also find contrasting requirements for BMP in the naive pre-implantation epiblast of mouse and human embryos. Finally, we show that NOTCH signalling is important for human epiblast survival. Our findings of conserved and species-specific factors that drive these early stages of embryonic development highlight the strengths of comparative species studies.
Asunto(s)
Embrión de Mamíferos , Estratos Germinativos , Embarazo , Femenino , Humanos , Embrión de Mamíferos/metabolismo , Desarrollo Embrionario/genética , Transducción de Señal , Implantación del EmbriónRESUMEN
Mouse embryos segregate three different lineages during preimplantation development: trophoblast, epiblast and hypoblast. These differentiation processes are associated with restricted expression of key transcription factors (Cdx2, Oct4, Nanog and Gata6). The mechanisms of segregation have been extensively studied in the mouse, but are not as well characterised in other species. In the human embryo, hypoblast differentiation has not previously been characterised. Here we demonstrate co-exclusive immunolocalisation of Nanog and Gata4 in human blastocysts, implying segregation of epiblast and hypoblast, as in rodent embryos. However, the formation of hypoblast in the human is apparently not dependent upon FGF signalling, in contrast to rodent embryos. Nonetheless, the persistence of Nanog-positive cells in embryos following treatment with FGF inhibitors is suggestive of a transient naïve pluripotent population in the human blastocyst, which may be similar to rodent epiblast and ES cells but is not sustained during conventional human ES cell derivation protocols.