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At least 649 records · Page 36Linked to original sources
PubMed1997

Border controls at the mammalian spinal cord: late-surviving neural crest boundary cap cells at dorsal root entry sites may regulate sensory afferent ingrowth and entry zone morphogenesis.

Boundary caps (BCs) form when neural crest cells, migrating ventrally alongside the neural tube, arrest at sites where axons will enter and exit. However, nothing is known of their subsequent fate and functions. We have found late-surviving neural crest BC cell clusters at proximal dorsal root entry sites throughout rat spinal cord development. Sensory afferents cross BCs to enter the spinal cord, while exiting astrocyte processes, destined to form the dorsal root entry zone (DREZ) after birth, are temporarily stalled in their vicinity. To test whether contact with BC cells influences neurite outgrowth from dorsal root ganglia, neurons were cultured on embryonic dorsal root/spinal cord cryosections. Neurites that entered CNS territory preferentially extended over BC cells. Thus, BC cells could be instrumental in regulating afferent ingrowth and DREZ morphogenesis in mammalian spinal cord development.

Animals↗
PubMed1993

Development, differentiation, and proliferation of macrophages in the rat yolk sac.

Immunohistochemical and immunoelectron microscopic investigation using anti-rat macrophage monoclonal antibody (mAb) RM-1 demonstrated the first emergence of immature macrophages within blood islands of fetal rat yolk sacs at fetal day 9. At fetal day 10, they matured into fetal macrophages, showed intense immunoreactivity to RM-1, developed lysosomal granules, endocytic vesicles or vacuoles, and extended fine cytoplasmic processes. By the rosetting assay with IgG-coated sheep erythrocyte antibody (IgG-EA), both the immature and mature fetal macrophages showed rosette formation and phagocytosis of IgG-EA, but they were negative for peroxidase (PO) reaction. At fetal day 11, fetal macrophages were observed in the mesenchymal layer of the yolk sacs. In the yolk sacs, no promonocytes or monocytes were observed, although there was a very minor population (less than 1%) of immature myeloid cells containing a few small PO-positive cytoplasmic granules from fetal day 11 on. After combination of the vitelline vessels to the embryonic cardiovascular system, fetal macrophages appeared in embryonic rat tissues. By [3H]thymidine autoradiography, yolk sac macrophages were demonstrated to possess a marked proliferative potential. These results suggest that fetal macrophages in the yolk sac differentiate from haematopoietic stem cells without passing through the promonocyte or monocyte stage, proliferate actively, and colonize the embryonic rat tissues.

Animals↗
PubMed2002

Immortalization of a primate bipotent epithelial liver stem cell.

Liver regeneration after partial hepatectomy results primarily from the simple division of mature hepatocytes. However, during embryonic and fetal development or in circumstances under which postnatal hepatocytes are injured, organ regeneration is believed to occur from a compartment of epithelial liver stem or progenitor cells with biliary and hepatocytic bipotentiality. The ability to identify, isolate, and transplant epithelial liver stem cells from fetal liver would greatly facilitate the treatment of hepatic diseases currently requiring orthotopic liver transplantation. Here we report the identification and immortalization by retrovirus-mediated transfer of the simian virus 40 large T antigen gene of primate fetal epithelial liver cells with a dual hepatocytic biliary phenotype. These cells grow indefinitely in vitro and express the liver epithelial cell markers cytokeratins 8/18, the hepatocyte-specific markers albumin and alpha-fetoprotein, and the biliary-specific markers cytokeratins 7 and 19. Bipotentiality of gene expression was confirmed by clonal analysis initiated from single cells. Endogenous telomerase also is expressed constitutively. After orthotopic transplantation via the portal vein, approximately 50% of the injected cells integrated into the liver parenchyma of athymic mice without tumorigenicity. Three weeks after transplantation, cells having seeded in the liver parenchyma expressed both albumin and alpha-fetoprotein but had lost expression of cytokeratin 19. These results provide strong evidence for the existence of a bipotent epithelial liver stem cell in nonhuman primates. This unlimited source of donor cells also should enable the establishment of a model of allogenic liver cell transplantation in a large animal closely related to humans and shed light on important questions related to liver organogenesis and differentiation.

Albumins↗
PubMed2003

Conservative segregation of maternally inherited CS histone variants in larval stages of sea urchin development.

Three sets of histone variants are coexisting in the embryo at larval stages of sea urchin's development: the maternally inherited cleavage stage variants (CS) expressed during the two initial cleavage divisions, the early histone variants, which are recruited into embryonic chromatin from middle cleavage stages until hatching and the late variants, that are fundamentally expressed from blastula stage onward. Since the expression of the CS histones is confined to the initial cleavage stages, these variants represent a very minor proportion of the histones present in the plutei larvae, whereas the late histone variants are predominant. To determine the position of these CS in the embryonic territories, we have immunolocalized the CS histone variants in plutei larvas harvested 72 h post-fertilization. In parallel, we have pulse labeled the DNA replicated during the initial cleavage cycle with bromodeoxyuridine (BrdU) and its position was further determined in the plutei larvas by immunofluorescence. We have found that the CS histone variants were segregated to specific territories in the plutei. The position in which the CS histone variants were found to be segregated was consistent with the position in which the DNA molecules that were replicated during the initial cleavage divisions were localized. These results strongly suggest that a specification of embryonic nuclei occurs at the initial cleavage divisions which is determined by a chromatin organized by CS histone variants.

Animals↗
PubMed1991

Repression of the Drosophila fushi tarazu (ftz) segmentation gene.

The striped expression of the Drosophila segmentation gene fushi tarazu in alternate parasegments of the early embryo is controlled by the 740 bp zebra element. Among multiple protein factors that bind to the zebra element, FTZ-F2 behaves as a transcriptional repressor of ftz. Point mutations in the zebra element which disrupt FTZ-F2 binding to DNA cause ectopic expression of zebra-lacZ activity in transformed embryos. The mutant constructs are expressed from the zygotic genome in preblastoderm embryos as early as the third nuclear division cycle. This unprecedented early transcription suggests that ftz requires active repression during initial nuclear division cycles, a novel type of embryonic gene regulation. A putative FTZ-F2 cDNA clone isolated by recognition site screening of an expression library was found to be identical in sequence with the zinc finger protein tramtrack (Harrison and Travers, 1990).

Animals↗
PubMed1983

Control of events during early cleavage of the mouse embryo: an analysis of the '2-cell block'.

Embryos from certain strains of mice do not develop into blastocysts when cultured in vitro from the 1- or 2-cell stages but arrest development as 2-cell embryos--a phenomenon referred to as the '2-cell block'. Reciprocal crosses between eggs and sperm of a 'blocking' (CFLP) and 'non-blocking' (F1) strain show that in this combination the genotype of the egg alone determines whether the embryo 'blocks' at the 2-cell stage (or continues retarded development to the 4- to 6-cell stage in a minority of cases). A comparison of molecular and cellular development in normal and 'blocked 2-cell' embryos was therefore undertaken to investigate the influence of these maternal components on early mouse development. The results show that the majority of 'blocked 2-cells' arrest development at a stage equivalent to the late 2-cell stage in terms of cellular and nuclear division, DNA synthesis, activation of the embryonic genome, qualitative and quantitative changes in amino acid uptake, polypeptide synthesis and morphological maturation of organelles. These observations are compatible with the notion that maternally inherited developmental information plays an important role in controlling early cleavage of the mouse embryo.

Animals↗
PubMed1985

Cell division cycle of cultured neural precursor cells from Drosophila.

In Drosophila neuroblast cells, which give rise to the embryonic nervous system, undergo a limited number of asymmetric cell divisions. These cell lineages result in the formation of clusters of neurons when neuroblasts are isolated and cultured. A significant proportion of these neural cell clusters (NCC) arise from individual precursor cells. The formation of NCC containing more than two neurons is repressed when DNA synthesis is inhibited. Cell division during NCC development was examined by [3H]thymidine autoradiography. The pattern of DNA synthesis by neural cells was that expected based on observations in situ. The pattern in individual NCC was consistent with single precursor origins for more than 80% of NCC, under our conditions of culture. Based on this, we show that the largest neural precursors at gastrulation undergo the most cell divisions in culture. The neuroblast cell division cycle averages approximately 1.5 hr, and is similar to that of blastoderm cells.

Animals↗
PubMed1990

Rod photoreceptor development in vitro: intrinsic properties of proliferating neuroepithelial cells change as development proceeds in the rat retina.

We describe a reaggregated cell culture system in which retinal neuroepithelial cells from embryonic rats proliferate extensively and give rise to rod photoreceptors on the same schedule in vitro as they do in vivo. Both the proliferative potential of the embryonic neuroepithelial cells and the timing of their differentiation into rods are not changed by the presence of a 50-fold excess of neonatal neural retinal cells, although many more of the embryonic cells develop into rods in these circumstances. In such mixed-age cultures, dividing neonatal cells proliferate much less and give rise to rods much sooner than do dividing embryonic cells, suggesting that the dividing cells at the two ages are intrinsically different. These and other findings suggest that both cell-cell interactions and an intrinsic program in neuroepithelial cells determine cell fate in the developing rat retina.

Aging↗
PubMed1994

Timetable of in vivo embryonic development in the grey short-tailed opossum (Monodelphis domestica).

The timing of development was examined in 496 embryos from female Monodelphis domestica collected at known time intervals after video recorded mating. Ovulation occurred approximately 20 hr (day 1) after mating, and fertilization was observed by 24 hr. Transport through the oviducts was rapid, and pronuclear stage embryos were recovered from the uterus as early as 24 hr after mating. Second cleavage had occurred by 55 hr after mating. Three-celled embryos were among those collected on day 3 after mating, indicating that asynchronous cleavage of blastomeres can occur from the two-cell stage. The four-cell stage persisted for approximately 24 hr, and embryos that had undergone third cleavage were first recovered 74 hr after mating. Embryos that had undergone fourth to fifth cleavage were found 96-100 hr (4 days) after mating and complete unilaminar blastocysts by 5.5 days after mating. Primary endoderm formed from an already distinct embryonic area of the unilaminar blastocyst early on day 7 after mating. Formation of the bilaminar blastocyst was completed rapidly, on day 7 after mating. The primitive streak appeared on day 10 after mating, and organogenesis rapidly ensued on a timetable similar to that reported for Didelphis virginiana (McCrady, 1938). Close contact with the maternal circulation was established on day 11 and by day 12 maternal and embryonic tissues could not be separated without damage. The length of the gestation period from fertilization to birth was approximately 13.5 days. These observations provide the basis for further embryological cellular and molecular studies of this species as a laboratory model for marsupial development.

Animals↗
PubMed1994

Origin and clonal relationship of common inhibitory motoneurons CI1 and CI3 in the locust CNS.

In the primordial thoracic ganglia of locust embryos, the bromodeoxyuridine (BrdU) technique for labelling proliferating cells and their progeny was combined with intracellular dye injection to investigate the origin and the clonal relationship of common inhibitory motoneurons. Common inhibitors 1 (CI1) and 3 (CI3) were found to be siblings, that is, they are produced by the division of one ganglion mother cell. This ganglion mother cell results from the first division of neuroblast 5-5, at about 30% of embryonic development. A large portion, at least, of the ganglion mother cells produced by subsequent divisions of neuroblast 5-5 give rise to interneurons with contralaterally ascending or descending axons and GABA-like immunoreactivity. Thus, CI1 and CI3 are more closely related to putative inhibitory interneurons than they are to other, that is, excitatory, motoneurons. Consistent with this, the CI somata are associated with cell bodies of putative inhibitory interneurons rather than with clusters of excitatory motoneuron somata. These results elicit speculations regarding the evolutionary origin of inhibitory motoneurons.

Animals↗
PubMed1994

The malignant stem cell.

A recent study of embryonic cells at organogenesis revealed that their nucleus was bare of cytoplasm along one section of the envelope, and that they formed aggregates in which nucleus to nucleus contact was a feature. Their behaviour could be divided into three stages, the first when the embryonic cell was small and motile, the second when cell aggregation took place and the third when differentiation occurred. The embryonic cell at organogenesis was considered to be committed and hence stem cell in nature. It is hypothesized that stem cells in the adult also start off as small, motile embryonic-like cells and progress through the same three stages. This embryonic-like structure and behaviour also applies to the malignant stem cell, and evidence is put forward to support this view. Finally the suggestion is made that metastases are due to the small size and motile nature of the malignant stem cell, and not due to a decrease in any adhesive forces between tumour cells.

Cell Differentiation↗
PubMed1999

What are the spermatocyte's requirements for successful meiotic division?

The consequences of error during meiotic division in spermatogenesis can be serious: aneuploid spermatozoa, embryonic lethality, and developmental abnormalities. Recombination between homologs is essential to ensure normal segregation; thus the spermatocyte must time division precisely so that it occurs after recombination between chromosomes and accumulation of the cell-cycle machinery necessary to ensure an accurate segregation of chromosomes. We use two systems to investigate meiotic division during spermatogenesis in the mouse: pharmacological induction of meiotic metaphase in cultured spermatocytes and transillumination-mediated dissection of stage XII seminiferous tubule segments to monitor progress through the division phase. By these approaches we can assess timing of acquisition of competence for the meiotic division phase and the temporal order of events as division proceeds. Competence for the meiotic division arises in the mid-pachytene stage of meiotic prophase, after chromosomes have synapsed and coincident with the accumulation of the cell-cycle regulatory protein CDC25C. The activity of both MPF and topoisomerase II are required. The earliest hallmarks of the division phase are nuclear envelope breakdown, followed by phosphorylation of histone H3 and chromosome condensation. These events are likely to be monitored by checkpoint mechanisms since checkpoint proteins can be localized in nuclei and DNA-damaging agents delay entry into the meiotic division phase. Understanding how the spermatocyte regulates its entry into the meiotic division phase can help clarify the natural mechanisms ensuring accurate chromosome segregation and preventing aneuploidy. J. Exp. Zool. (Mol. Dev. Evol.) 285:243-250, 1999.

Animals↗
PubMed1984

Growth and differentiation of pluripotent embryonal carcinoma cells in the Snell dwarf mouse.

To investigate the influence of hormones on the process of cellular differentiation the growth and differentiation of a transplantable tumour, induced by inoculation of pluripotent mouse embryonal carcinoma (EC) cells have been studied in athymic nude mice and, normal and hypopituitary Snell dwarf mice. All athymic nude mice developed tumours independent of the numbers of cells inoculated. In contrast, the tumour percentage in normal Snell mice was lower, showing a dose-dependent increase of takes. In dwarfs tumour percentage was comparable with that observed in normal Snell mice. The morphological differentiation of teratocarcinomas grown in athymic nude mice, normal and dwarfed Snell mice shows derivatives of all three germ layers next to undifferentiated embryonal carcinoma cells. This suggests that the pituitary hormonal deficiencies of the dwarfs (growth hormone, thyroid stimulating hormone and prolactin) did not influence the tumour induction nor the development of the different tissues present in this type of tumour.

Animals↗
PubMedDate not supplied

Mathematical modeling of human embryonic and fetal growth rates.

A mathematical model for human embryonic/fetal growth data from implantation to birth is developed. In previous work, it was shown that an unbiased estimate for human fetal growth data from about day 50 post-conception until term could be calculated from the Gompertz equation. This period represents a range of embryonic/fetal weights from one to 3500 g. When the Gompertz equation is extended, with no change of parameters, to the prenatal period before 50 days, the predicted weights have a consistent bias which might have a biological basis. Early embryonic growth immediately following fertilization is exponential; i.e., one cell goes to 2, then 4, then 8... etc., with essentially no decrease in relative growth rate. Except for possible small changes in cell size and cell mitosis cycle time, such exponential growth can be considered as a special case of the Gompertz equation with a, the relative rate of decrease of the relative growth rate, equal to zero. The relative growth rate begins to decrease about 20 days post-conception, at the time of cell differentiation into organ precursors. Although the "Hayflick Limit" of the maximum of 50 to 60 cell divisions for human cells would tend to cause a decrease in growth rate, it can be shown that the effect is insignificant during embryonic/fetal growth. The observed decrease in the growth rate might be a result of a decreasing fraction of cells in the pool of dividing cells. For the Gompertz equation model, a at this time changes from zero to a positive number. Analysis of fetal growth data shows that a rapidly becomes large and then decreases over a period of several days to become a constant positive value for the remainder of the prenatal term. Good fits of empirical embryonic/fetal growth data were obtained by nonlinear regression with calculation of the embryonic/fetal weights through numerical integration of the differential Gompertz equations and the functionality of alpha.

Body Weight↗
PubMed2003

Disruption of the regulatory beta subunit of protein kinase CK2 in mice leads to a cell-autonomous defect and early embryonic lethality.

Protein kinase CK2 is a ubiquitous protein kinase implicated in proliferation and cell survival. Its regulatory beta subunit, CK2beta, which is encoded by a single gene in mammals, has been suspected of regulating other protein kinases. In this work, we show that knockout of the CK2beta gene in mice leads to postimplantation lethality. Mutant embryos were reduced in size at embryonic day 6.5 (E6.5). They did not exhibit signs of apoptosis but did show reduced cell proliferation. Mutant embryos were resorbed at E7.5. In vitro, CK2beta(-/-) morula development stopped after the blastocyst stage. Attempts to generate homozygous embryonic stem (ES) cells failed. By using a conditional knockout approach, we show that lack of CK2beta is deleterious for mouse ES cells and primary embryonic fibroblasts. This is in contrast to what occurs with yeast cells, which can survive without functional CK2beta. Thus, our study demonstrates that in mammals, CK2beta is essential for viability at the cellular level, possibly because it acquired new functions during evolution.

Animals↗
PubMed1998

[Nucleolar apparatus of proliferating and differentiating cells of human embryonic neocortex during formation of the cortical plate].

Human neocortex was studied using light and electron microscopy in embryos 6-10 wks of development. Vast majority of proliferating cells was established to be concentrated in ventricular zone. Nuclear, nucleolar and cytoplasmic organelle structure indicate various level of synthetic processes activity in cells of different layers of the developing human neocortex. The dynamics in nucleolar number in the cells of ventricular zone and cortical plate was demonstrated.

Cell Differentiation↗
PubMedDate not supplied

[Embryonic stem cells: from fundamental studies--to clinical application].

A short history of embryonic stem cell (ESC) discovery, cell line isolation, phenotyping and cell behavior both in situ and in vitro is outlined. The path of ESC differentiation into restricted specialized cell types mediated by signal network in culture and by grafting cell into recipient tissues is considered. Potentialities of ESC as the generator of spare parts of organs for regenerative medicine and related bioethical issues are briefly outlined.

Animals↗
PubMed1989

Generation of cell diversity during early embryogenesis in the nematode Caenorhabditis elegans.

Caenorhabditis elegans zygotes undergo a series of four differentiative divisions to generate 5 somatic founder cells and a germ-line progenitor cell by the 16- to 24-cell stage of embryogenesis. The pattern of divisions, cell positions, and development of the embryonic cells are invariant from embryo to embryo. Through a combination of embryo manipulation, treatment of embryos with pharmacologic agents, and genetic analysis of maternal-effect embryonic-lethal mutants, researchers in several laboratories have investigated when and how cell differences are generated and cell fates are specified during embryogenesis: 1. Most blastomeres develop in a cell-autonomous manner. They do not need to undergo cell division and they do not require their normal neighbors to express differentiation products characteristic of their lineage. In embryos in which specific cells have been ablated, the fates of neighboring cells do not change to compensate for the missing cells. These observations suggest that most embryonic cells are determined by lineally transmitted internally segregated information. 2. There is at least one clear-cut example of inductive interactions during early development. The anterior daughter of AB gives rise to hypodermis, neurons, pharyngeal muscles, and body wall muscles. Interactions between ABa cells and P1-derived blastomeres are required between the 4- and 28-cell stage for ABa to generate pharyngeal and body wall muscles. ABa appears to be directed to generate hypodermis by internally segregated cues and directed to generate muscle by external cues. 3. Certain of the early internal segregation events require the participation of microfilaments. Disruption of the microfilament array leads to the missegregation of germ granules and of the potential of cells to undergo unequal germ-line-like divisions. Microfilaments may be involved in many other segregation events as well. 4. Several maternal-effect lethal mutants also perturb zygotic segregation events. These par mutants, which divide symmetrically and fail to segregate germ granules, may identify genes whose products interact with microfilaments or otherwise participate in cytoplasmic localization during the early divisions.

Animals↗