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PubMedDate not supplied

Sex chromosome determination in extragonadal teratomas by interphase cytogenetics: clues to histogenesis.

Teratomas are neoplasms that are composed of tissues from all three germinal layers. The exact histogenetic origin of teratomas, however, is still controversial. In order to gain more insight into histogenesis of extragonadal teratomas (EGTs), the gonosomal status in 13 congenital EGTs was studied by means of interphase cytogenetics using nonradioactive in situ hybridization (NISH) with centromere-specific DNA probes. By use of this technique a direct correlation of cytogenetic results with morphology was possible. In all EGTs analyzed the gonosomal status in tissues derived from the different germinal layers was identical to that of the nontumorous fetal and placental tissue. This was true irrespective of localization, age, histological type, and classification of the EGT. Our results strongly suggest that EGTs arise from pluripotent diploid precursor cells, for example, either premeiotic germ cells that have not yet undergone the first meiotic division or pluripotent ectopic embryonal or extraembryonal cells. Our data do not support the theory of parthenogenetic EGT development, at least in males.

Cell Differentiation↗
PubMed1998

The comparison of primordial germ cell populations in embryos of KE and CBA inbred strains of mice.

The changes in primordial germ cell (PGC) populations were compared in embryos of two inbred strains of mice-KE and CBA/Kw on 11, 12, 13 and 14 day of foetal life. The number of PGCs did not differ in 11-day embryos of both strains. In 12-day CBA/Kw embryos the proliferation rate of PGCs was higher and the number of PGC was significantly higher than in 12-day KE embryos. However, on subsequent days the PGC proliferation rate decreased in CBA/Kw but rapidly increased in KE embryos, leading to significantly higher number of PGCs in 14-day KE embryos. These differences in proliferation rate between KE and CBA/Kw PGCs can be regarded as the reason of strong selection against CBA/Kw derived gametes observed in KE<-->CBA aggregation chimaeras.

Alkaline Phosphatase↗
PubMed2006

HIF-2alpha regulates Oct-4: effects of hypoxia on stem cell function, embryonic development, and tumor growth.

The division, differentiation, and function of stem cells and multipotent progenitors are influenced by complex signals in the microenvironment, including oxygen availability. Using a genetic "knock-in" strategy, we demonstrate that targeted replacement of the oxygen-regulated transcription factor HIF-1alpha with HIF-2alpha results in expanded expression of HIF-2alpha-specific target genes including Oct-4, a transcription factor essential for maintaining stem cell pluripotency. We show that HIF-2alpha, but not HIF-1alpha, binds to the Oct-4 promoter and induces Oct-4 expression and transcriptional activity, thereby contributing to impaired development in homozygous Hif-2alpha KI/KI embryos, defective hematopoietic stem cell differentiation in embryoid bodies, and large embryonic stem cell (ES)-derived tumors characterized by altered cellular differentiation. Furthermore, loss of HIF-2alpha severely reduces the number of embryonic primordial germ cells, which require Oct-4 expression for survival and/or maintenance. These results identify Oct-4 as a HIF-2alpha-specific target gene and indicate that HIF-2alpha can regulate stem cell function and/or differentiation through activation of Oct-4, which in turn contributes to HIF-2alpha's tumor promoting activity.

Alleles↗
PubMed2001

Asymmetric inheritance of radial glial fibers by cortical neurons.

Recent studies demonstrated the neuronogenic role of radial glial cells (RGCs) in the rodent. To reveal the fate of radial glial processes, we intensively monitored divisions of RGCs in DiI-labeled slices from the embryonic day 14 mouse cortex. During RGC division, each pia-connected fiber becomes thin but is neither lost nor divided; it is inherited asymmetrically by one daughter cell. In divisions that produce a neuron and a progenitor, the neuron inherits the pial fiber, also grows a thick ventricular process for several hours, and is therefore indistinguishable from the progenitor RGC. The ventricular process in the radial glial-like neuron ("radial neuron") then collapses, leading to ascent of the neuron by using the "recycled" radial fiber.

Aging↗
PubMed1993

Heat-shock gene expression and cell cycle changes during mammalian embryonic development.

Synchronized regulation of cell division during gastrulation is essential for the regional proliferation of cells and pattern formation of the early CNS. The neural plate and neuroectoderm cells are a rapidly dividing and differentiating population of cells with a unique and rapid heat-shock response. Heat shock and the heat-shock genes were studied during neural plate development in a whole rat embryo culture system at 9.5-11.5 days. A lethal shock can cause cell death and severe developmental defects to the forebrain and eye during organogenesis. Heat shock can also result in acquired thermotolerance whereby cell progression is delayed at the G1/S and S/G2 boundaries of the cell cycle. This delay in cell cycle progression caused an overall lengthening of the cell cycle time of at least 2 hr. The heat shock genes may therefore function as cell cycle regulators in neuroectoderm induction and differentiation. The kinetics and expression of the hsp genes were examined in neuroectodermal cells by flow cytometry and Northern analysis. The levels of hsp mRNA 27, 71, 73, and 88 were identified following exposure at 42 degrees C (nonlethal), 43 degrees C (lethal) and 42 degrees/43 degrees C (thermotolerant) heat shock. Examination of hsp gene expression in the neural plate showed tight regulation in the cell cycle phases. Hsp 88 expression was enhanced at Go and hsp71 induction at G2 + M of the cell cycle. Cells exposed to a thermotolerant heat shock of 42 degrees C induced hsp71 mRNA expression in all phases of the cell cycle with the mRNA levels of hsp27, 73, and 88 increased but relatively constant. Following a lethal heat shock, dramatic changes in hsp expression were seen especially enhanced hsp71 induction in late S phase. The regulated expression of hsps during the cell cycle at various phases could play a unique and important role in the fate and recovery of neuroectoderm cells during early mammalian embryo development.

Animals↗
PubMed1980

Cell cycle and experimental pattern duplication in the chick wing during embryonic development.

Transient stimulation of cell division within chick wingbud mesenchyme is associated with the reorganization of limb pattern that follows insertion of a small graft from the posterior zone of limb polarizing activity into the anterior border of a host bud. This increase is initiated as an enhanced rate of entry to S phase, correlated with a decrease in packing density among mesenchyme cells, through much of the limb rudiment a few hours after the operations.

Animals↗
PubMed1989

Chromosome malsegregation and embryonic lethality induced by treatment of normally ovulated mouse oocytes with nocodazole.

The mouse egg is ovulated with its nucleus arrested at the metaphase-II stage of meiosis. Sperm entry triggers the completion of the second meiotic division. It has been speculated that damage to the meiotic spindle of normally ovulated eggs at around the time of sperm entry could result in chromosome malsegregation and the death of conceptuses with numerical chromosome anomalies. This hypothesis was tested using nocodazole, a microtubule inhibitor. Nocodazole was administered either to maturing preovulatory oocytes or to normally ovulated eggs at one of the following stages: (1) the time of sperm entry, (2) early pronuclear stage, (3) pronuclear DNA synthesis, (4) prior to first cleavage division, (5) early 2-cell stage, or (6) prior to the second cleavage division. Little or no effect was observed for treatment times other than the time of sperm entry, when the egg is being activated to complete the second meiotic division. Remarkably high frequencies of embryonic lethality, expressed at around the time of implantation, were induced at this stage. Cytogenetic analysis of first cleavage metaphases of zygotes treated at the time of sperm entry revealed a high incidence of varied numerical chromosome anomalies, with changes in ploidy being predominant.

Aneuploidy↗
PubMed1992

The foramen meningo-orbitale and its relationship to the development of the ophthalmic artery.

The incidence of the foramen meningo-orbitale is reported from a sample of 50 adult dried skulls. The foramen meningo-orbitale is not an inconsistent finding, being identifiable in half of the samples studied. Multiple foramina may exist. Although the location of the foramen meningo-orbitale is not fixed, it lies along or near the suture leading superolaterally from the superior orbital fissure. The foramen represents the remnant of an embryonic conduit for the supraorbital division of the stapedial artery en route to the orbit and the developing ophthalmic artery. An alternative, more medial, pathway exists through the superior orbital fissure. The embryonic anastomosis that occurs between the internal and external carotid systems does not occur at the level of this foramen, but closer to the optic nerve as a portion of the primitive 'ring' artery. The term 'stapedial-ophthalmo-lacrimal' foramen is proposed to proclaim the embryonic significance of this foramen.

Humans↗
PubMed1996

Onset of C. elegans gastrulation is blocked by inhibition of embryonic transcription with an RNA polymerase antisense RNA.

Cleavage and gastrulation initiation in Caenorhabditis elegans embryos are characterized by an invariant temporal and spatial pattern of cell divisions and cell movements. Although bulk embryonic transcription does not begin until gastrulation onset, some transcription can be detected as early as the 4-cell stage. To determine whether any early transcripts are required for normal cleavage-stage patterning, we blocked transcription in embryos by injecting hermaphrodite parental gonads with RNA antisense to the ama-1 gene, which encodes the large subunit of RNA polymerase II. This treatment prevented the expression of a reporter gene driven by an early embryonic promoter but did not detectably perturb the maternally controlled segregation of the germ line P granules or the pattern of cell division through the first four cleavages. In the fifth cell cycle, however, the two endodermal precursor (E) cells divided early and abnormally and failed to initiate gastrulation. The embryos arrested between the sixth and seventh cell cycles with less than 100 cells. These results indicate that embryonically transcribed gene products are required for gastrulation initiation. They also demonstrate the efficacy of a method for blocking embryonic transcription that may be useful in other organisms.

Animals↗
PubMed1993

Effect of zidovudine on preimplantation murine embryos.

It previously has been demonstrated that zidovudine (AZT) is lethal to early murine embryos. The effect of the drug on pre- and postimplantation embryos was examined to delineate the timing of this toxicity and to investigate its possible mechanisms. Embryos exposed in the whole mouse during preblastocyst development were unable to proceed beyond the blastocyst stage. Similarly, when two-cell embryos harvested from unexposed females were exposed to low-concentration (1 microM) AZT in vitro over 24 h, development beyond the blastocyst stage was inhibited. In contrast, drug exposure during in vitro blastocyst and postblastocyst development resulted in little or no morphologic toxicity. Further investigation revealed that preblastocyst AZT exposure resulted in the development of blastocysts with significantly lower cell numbers than control embryos. While embryonic exposure to AZT at the blastocyst and postblastocyst stages also resulted in retarded cell division, the effects were milder than those recorded after preblastocyst exposure. These data demonstrate that the critical period of AZT toxicity toward murine embryos is between ovulation and implantation and indicate that AZT directly suppresses cell division in the preimplantation embryo.

Animals↗
PubMedDate not supplied

[Embryonic stem cells: spontaneous and directed differentiation].

The specific structural features of embryonic stem cells and embryoid bodies and mechanisms of their differentiation in different cell types are considered. The mouse embryonic stem cells (line R1) formed multilayer colonies which enlarged as a result of fast cell division. Embryoid bodies that derived from embryonic stem cells consisted of an outer layer, an inner layer, and an internal cavity. The structure of cells of the outer and inner layers markedly differed. Spontaneous and directed differentiation of embryoid bodies is determined by some unspecific and specific factors (growth and differentiation factors and extracellular matrix proteins). Retinoic acid, the most commonly used inducer of differentiation of the embryonic stem cells, induces different types of differentiation when applied at different concentrations. The sequence of expression of tissue specific genes and proteins during differentiation of the embryonic stem cells in vitro is similar to that in vivo.

Animals↗
PubMed1983

DNA and cholesterol biosynthesis in synchronized embryonic rat fibroblasts. II. Effects of sterol biosynthesis inhibitors on cell division.

The relationships between cholesterogenesis and cell division were studied by using two inhibitors of hydroxymethylglutaryl-CoA reductase activity--25-hydroxycholesterol and compactin. The effects of both compounds on DNA synthesis were compared in synchronized rat fibroblasts cultured in a cholesterol-containing medium. Compactin did not inhibit DNA synthesis, except after a long time of contact and at high and almost cytotoxic concentrations. 25-Hydroxycholesterol inhibited DNA synthesis (without cytotoxic effects) after only 9-16 h of contact, depending on the phase of the cell cycle at which this compound was added to the culture medium. Sensitivity of cells to 25-hydroxycholesterol was maximal at the end of the S phase/beginning of the G2M phase. The rapid effect of 25-hydroxycholesterol on DNA synthesis appears to be separate from the inhibitory effect on sterol or non-sterol mevalonate-derived compound synthesis. Indeed, under our experimental conditions, the suppression of cholesterol biosynthesis is compensated by the presence of cholesterol in the culture medium, as demonstrated by the lack of effect of compactin on DNA synthesis; moreover, addition of mevalonolactone to the culture medium did not reverse the effect of 25-hydroxycholesterol. 25-Hydroxycholesterol could inhibit DNA synthesis by a direct action on the nucleus, after transfer by the intermediary of a specific hydroxysterol-binding protein.

Acetates↗
PubMed2003

Survivin - an anti-apoptosis protein: its biological roles and implications for cancer and beyond.

Survivin is a protein that inhibits apoptosis and regulates cell division. Survivin contains a baculovirus inhibitor of apoptosis repeat (BIR) protein domain that classifies it as a member of the inhibitor of apoptosis protein (IAP) family. Survivin inhibits apoptosis, via its BIR domain, by either directly or indirectly interfering with the function of caspases. Survivin is also a chromosomal passenger protein that is required for cell division. Survivin is expressed in embryonic tissues as well as in the majority of human cancers, but is not expressed in most normal adult tissues. The cancer-specific expression of survivin, coupled with its importance in inhibiting cell death and in regulating cell division, makes it a useful diagnostic marker of cancer and a potential target for cancer treatment. Recently, there is emerging evidence that survivin is involved in tissue injury and its healing. Understanding the mechanism of survivin function can potentially allow for the development of therapeutic strategies for cancer and other diseases.

Animals↗
PubMed2000

Control of plant growth and development through manipulation of cell-cycle genes.

The plant embryo is a relatively simple structure consisting of a primordial shoot and root, whose development is frozen in the form of a seed. Most development of the mature plant takes place post-embryonically, and is the consequence of cell division and organogenesis in small regions known as meristems, which originate in the embryonic shoot and root apices. Significant recent progress has been made in understanding the mechanisms that control the plant cell cycle at a molecular level, and the first attempts have been made to control plant growth through modulation of cell-cycle genes. These results suggest that there is significant potential to control plant growth and architecture through manipulation of cell division rates. However, a full realisation of the promise of such strategies will probably require a much greater understanding of cell division control and how its upstream regulation is co-ordinated by spatial relationships between cells and by environmental signals.

Cell Cycle↗
PubMed2006

A mosaic genetic screen for novel mutations affecting Drosophila neuroblast divisions.

BACKGROUND: The asymmetric segregation of determinants during cell division is a fundamental mechanism for generating cell fate diversity during development. In Drosophila, neural precursors (neuroblasts) divide in a stem cell-like manner generating a larger apical neuroblast and a smaller basal ganglion mother cell. The cell fate determinant Prospero and its adapter protein Miranda are asymmetrically localized to the basal cortex of the dividing neuroblast and segregated into the GMC upon cytokinesis. Previous screens to identify components of the asymmetric division machinery have concentrated on embryonic phenotypes. However, such screens are reaching saturation and are limited in that the maternal contribution of many genes can mask the effects of zygotic loss of function, and other approaches will be necessary to identify further genes involved in neuroblast asymmetric division. RESULTS: We have performed a genetic screen in the third instar larval brain using the basal localization of Miranda as a marker for neuroblast asymmetry. In addition to the examination of pupal lethal mutations, we have employed the MARCM (Mosaic Analysis with a Repressible Cell Marker) system to generate postembryonic clones of mutations with an early lethal phase. We have screened a total of 2,300 mutagenized chromosomes and isolated alleles affecting cell fate, the localization of basal determinants or the orientation of the mitotic spindle. We have also identified a number of complementation groups exhibiting defects in cell cycle progression and cytokinesis, including both novel genes and new alleles of known components of these processes. CONCLUSION: We have identified four mutations which affect the process of neuroblast asymmetric division. One of these, mapping to the imaginal discs arrested locus, suggests a novel role for the anaphase promoting complex/cyclosome (APC/C) in the targeting of determinants to the basal cortex. The identification and analysis of the remaining mutations will further advance our understanding of the process of asymmetric cell division. We have also isolated a number of mutations affecting cell division which will complement the functional genomics approaches to this process being employed by other laboratories. Taken together, these results demonstrate the value of mosaic screens in the identification of genes involved in neuroblast division.

Animals↗