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S C Barton

Publications and source records attributed to S C Barton.

At least 73 records · Page 4Linked to original sources
PubMed1988

Influence of chromosomal determinants on development of androgenetic and parthenogenetic cells.

We have examined the role of germline-specific chromosomal determinants of development in the mouse. Studies were carried out using aggregation chimaeras between androgenetic----fertilized embryos and compared with similar parthenogenetic----fertilized chimaeras. Several adult chimaeras were found with parthenogenetic cells but none were found with androgenetic cells. Analysis of chimaeras at mid-gestation showed that parthenogenetic cells were detected in the embryo and yolk sac but that androgenetic cells were found only in the trophoblast and yolk sac and not in the embryo. The contribution of parthenogenetic cells to the embryo and yolk sac was increased by aggregating 2-cell parthenogenetic and 4-cell fertilized embryos but the contribution of parthenogenetic cells in extraembryonic tissues remained negligible even after aggregation of 4-cell parthenogenetic and 2-cell fertilized embryos. Furthermore, parthenogenetic cells were primarily found in the yolk sac mesoderm and not in the yolk sac endoderm. These results suggest that maternal chromosomes in parthenogenetic cells permit their participation in the primitive ectoderm lineage but these cells are presumably eliminated by selective pressure or autonomous cell lethality from the primitive endoderm and trophectoderm lineages. Conversely paternal chromosomes in androgenetic cells confer opposite properties since the embryonic cells can be detected in the trophoblast and the yolk sac but not in the embryos, presumably because they are eliminated from the primitive ectoderm lineage. The spatial distribution of cells with different parental chromosomes may occur partly because of differential expression of some genes, such as proto-oncogenes, and partly due to their ability to respond to a variety of diffusible growth factors.

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PubMed1987

Experimental reconstruction of mouse eggs and embryos: an analysis of mammalian development.

The scope of experimental approaches applicable to the study of mammalian eggs and embryos has advanced in recent years to provide unprecedented opportunities for understanding mammalian embryology. Amongst these significant advances has been the ability to alter the genetic constitution of eggs by pronuclear and nuclear transplantation as well as by the introduction of specific cloned genes into eggs and embryos. These techniques can be used in conjunction with the experimental reconstruction of preimplantation embryos to investigate more precisely a number of aspects of mammalian embryology. Recently, a most intriguing aspect of development has been uncovered, one that is apparently unique to mammals; experiments have revealed that the parental genomes are not functionally equivalent during embryogenesis. Hence, the parental origin of chromosomes determines their influence during embryogenesis. The mechanistic aspects responsible for the germ line modifications of homologous chromosomes, their role during development, and the wide-ranging implications of these findings for mammalian development have yet to be fully defined. An understanding of this process will provide the basis for developing genetic and reproductive strategies that can be applied to domestic animals and to humans.

Animals↗
PubMed1987

Nuclear cytoplasmic interactions following nuclear transplantation in mouse embryos.

We have investigated the development of reconstituted embryos in which enucleated 1- or 2-cell embryos received various advanced nuclei. Enucleated 1-cells developed to the blastocyst stage only when an early 2-cell donor nucleus was transferred but very rarely if the donor nucleus was derived from a late 2-cell, early 4-cell or mid 8-cell embryo. Although an 8-cell nucleus could only support development of an enucleated zygote to the 2-cell stage, it did express the hsp 68/70 X 10(3) Mr proteins that are characteristic of the first embryonic gene activity. These polypeptides were absent in enucleated zygotes that did not receive a donor nucleus. Moreover, an 8-cell nucleus transferred to an enucleated late 2-cell blastomere could also support preimplantation development provided that the nuclear:cytoplasmic ratio was maintained as in intact 2-cell blastomeres. 8-cell nuclei transferred to zygotes that retained at least one pronucleus were able to support development to the blastocyst stage provided that the pronucleus was both fully transcriptionally active and present beyond the late 1-cell stage. This study suggests an active and continued helper role of the resident pronucleus for the participation by an 8-cell nucleus in reconstituted eggs.

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PubMed1986

Nuclear transplantation in the mouse: heritable differences between parental genomes after activation of the embryonic genome.

Paternal and maternal genomes apparently have complementary roles during embryogenesis in the mouse, and both are essential for development to term. However, there is no direct evidence to show that functional differences between parental genomes remain intact after activation of the embryonic genome at the 2-cell stage. In this study we demonstrate that transfer of paternal or maternal nuclei from early haploid preimplantation embryos back to fertilized eggs from which one pronucleus was removed resulted in development to term, but only if the remaining pronucleus was of the parental type opposite to the donor nucleus. Hence, functional differences between parental chromosomes are heritable and they survive activation of the embryonic genome and probable reprogramming of donor embryonic nuclei by epigenetic factors in the egg cytoplasm.

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PubMed1985

Development of gynogenetic and parthenogenetic inner cell mass and trophectoderm tissues in reconstituted blastocysts in the mouse.

The developmental potential of inner cell mass (ICM) and trophectoderm (TE) derived from parthenogenetic or biparental gynogenetic embryos was examined in reconstituted blastocysts with normal TE or ICM, respectively. The results demonstrate that when a normal ICM was introduced inside a trophectoderm vesicle derived from parthenogenetic or gynogenetic blastocysts, postimplantation development was characterized by the almost complete failure of trophoblast proliferation and without compensating cellular contribution from the normal ICM to the outer trophoblast lineage. Consequently, the normal ICMs also failed to develop adequately and only a few retarded embryos were detected on day 11-12 of pregnancy. In most respects, development of these reconstituted blastocysts resembled that obtained with unoperated gynogenetic and a parthenogenetic blastocyst. By contrast, an ICM from a parthenogenetic or gynogenetic embryo introduced inside a normal trophectoderm vesicle induced substantial proliferation of the trophoblast but again without a detectable cellular contribution from the ICM to the outer trophoblast lineage. However, with the improved development of the trophoblast, both the parthenogenetic and gynogenetic ICMs developed substantially better and without a detectable cellular contribution from the TE to the embryo. Almost all the embryos developed at least up to the 25-somite stage and many of them reached the 30- to 40-somite stage. Some of the most advanced day-11 and -12 gynogenones and parthenogenones yet seen have now been obtained in this way. Nevertheless, all the embryos were still smaller than the equivalent control embryos and showed signs of some tissue degeneration. The yolk sac was also suboptimal with poor blood supply and may need to be improved to obtain further improvement in the development of the embryos. The combined results demonstrate that the trophoblast proliferates very poorly even in the presence of a normal ICM, if the TE tissue lacks a paternal genome. However, ICM tissues which lack a paternal genome can develop to an advanced embryonic stage if they are introduced inside a normal trophectoderm vesicle. The results give further insight into the differential roles of maternal and paternal genomes during development of the embryo and extraembryonic tissues in the mouse.

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PubMed1984

Spatial distribution of blastomeres is dependent on cell division order and interactions in mouse morulae.

Spatial distribution of blastomeres was examined in 16- to 30-cell morulae obtained from aggregates of 1/2----1/2 and 1/2----2/4 blastomeres. The advanced blastomeres (2/4) contributed disproportionately more inner cells while there was a corresponding decline in the contribution from the delayed blastomere (1/2) so that a balance between the total number of inner and outer cells was retained. There was, however, no marked change in the relative number of outer cells. It is suggested that once formed, the inner more adhesive cells divide relatively faster than the outer cells whose behaviour is dictated by the inner cells. The outer less adhesive cells spread over the inner cells; cell spreading is incompatible with division. The degree to which cell spreading and retardation of division of outer cells occurs may be dictated by the number of inner cells present at any one time and this partly determines the entry of further cells inside. The suggested mechanism for cell allocation is highly flexible and, indeed, essential to encompass the wide variety of patterns of cell interactions and distribution observed in morulae. It is also proposed that the retardation of division of outer cells may trigger differentiation of trophectoderm by inducing endoreduplication and the blastomeres delayed from dividing for the longest period of time may mark down the abembryonic pole and establish the embryonic-abembryonic axis.

Animals↗
PubMed1984

Cryoprotection of day-4 mouse embryos by methanol.

Methanol was examined as a cryoprotective additive that permits the direct transfer of frozen--thawed Day-4 mouse embryos to foster mothers without dilution of the cryoprotectant. Methanol permeated the embryos rapidly, was not toxic and exerted a cryoprotective action. The highest level of survival (50%) of embryos in vitro was observed after equilibration in Medium PB1 containing 3.0 M-methanol, slow cooling (0.5 degrees C/min) to a temperature between -30 and -40 degrees C, rapid cooling (800 degrees C/min) and storage in liquid nitrogen (-196 degrees C), rapid warming (800 degrees C/min), and rapid dilution. A high rate of development in vivo to late-stage fetuses (up to 81%) was observed when cryopreserved embryos were transferred to pseudopregnant recipients immediately after thawing.

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PubMed1983

Development of gynogenetic eggs in the mouse: implications for parthenogenetic embryos.

Mouse eggs with different genetic constitutions were prepared by micromanipulation of fertilized diploids and triploids. The diploid gynogenones, activated by the male gamete which was then removed, developed at best to about the 25-somite stage as did the genetically similar diploid parthenogenones stimulated to develop in the complete absence of the male gamete. The failure of development to term in both cases may be due to homozygosity and does not appear to be due to a lack of extragenetic contribution from spermatozoa.

Animals↗
PubMed1983

Microdissection of the mouse egg.

A rapid and efficient method for microdissection of the mouse egg is described. The dissection is carried out in hanging drops of medium surrounded by heavy liquid paraffin oil at room temperature. Eggs are first deformed into a cylindrical shape and then dissected at a predetermined site with a glass needle on a Leitz micromanipulator. The survival rate of the dissected fragments is 75-90% and between 20 and 30 eggs can be dissected in an hour. Development of the dissected eggs is at least as good as that described after other types of manipulation. Cytoplasts and karyoplasts of various sizes can be prepared, as well as gynogenetic and androgenetic eggs with different amounts of cytoplasm. This procedure may help to examine nuclear-cytoplasmic interactions in eggs reconstituted from a variety of fragments.

Animals↗
PubMed1982

Interactions of blastomeres suggest changes in cell surface adhesiveness during the formation of inner cell mass and trophectoderm in the preimplantation mouse embryo.

Whole 8-cell morulae can be aggregated with isolated inner cell masses from blastocysts. On examining semithin light microscope sections of such aggregates we found that cells of the morula changed shape and spread over the surface of the ICM, thus translocating it to the inside of the aggregate. Using single cells from 8-cell embryos in combination with single cells from other stage embryos or isolated ICMs we show that 1/8 blastomeres spread over other cells providing a suitably adhesive surface. The incidence of spreading is high with inner cells from 16-cell embryos (56%) and 32-cell embryos (62%) and isolated inner cell masses (64%). In contrast, the incidence of spreading of 1/8 blastomeres is low over outer cells from 16-cell embryos (26%) and 32-cell embryos (13%). Blastomeres from 8-cell embryos do not spread over unfertilized 1-cell eggs, 1/2 or 1/4 cells or trophectoderm cells contaminating isolated ICMs. When 1/8 cells are aggregated in pairs they flatten on one another (equal spreading) as occurs at compaction in whole 8-cell embryos. However, if 1/8 is allowed to divide to 2/16 in culture one of the cells engulfs the other (51-62% pairs). Based on the ideas of Holtfreter (1943) and Steinberg (1964, 1978) these results are interpreted to indicate an increase in adhesiveness at the 8-cell stage as well as cytoskeletal mobilization. Following the 8-cell stage there is an increase in adhesiveness of inside cells while the outside cells decrease in adhesiveness. The difference in adhesiveness between inside and outside cells in late morulae is probably central to the divergent differentiation of (inner) ICM and (outer) trophectoderm cell populations.

Animals↗
PubMed1978

Isolation and development of the inner cell mass after exposure of mouse embryos to calcium ionophore A23187.

Compacted morulae and blastocysts were obtained from CBA, BALB/c and CFLP strains of mice. The embryos were incubated in medium containing 2 X 10(-5) M or 2 X 10(-6) M ionophore A23187. With 2 X 10(-6) M ionophore, morulae survived for up to 12 h showing slight decompaction. Normal development resumed when the morulae were explanted to fresh medium. There was no detectable effect on blastocysts. With 2 X 10(-5) M ionophore, morulae survived for about 20 min and then extensive cell death occurred after this time. With blastocysts however, selective lysis of trophectoderm cells occurred after approximately 30 min following their swelling and vesiculation but the inner cell mass cells (ICM) remained apparently intact and viable. Nearly 80% of the early blastocysts obtained 87 h post-ovulation and all of the late blastocysts used after 12 h in culture (99 h blastocysts) showed this response. Individual fluid accumulating cells were detected in a few isolated ICMs after their overnight culture in vitro, especially in those obtained from early blastocysts, but the majority of the ICMs did not have these cells. All aggregates of three to five ICMs, except one which reformed into a blastocyst, developed as embryoid bodies after 2 days in culture and these survived for up to 10 days; in some cases they developed into cystic embryoid bodies or attached to the culture dish displaying a variety of cell types. The development of the isolated ICMs in vivo was judged to be normal after their transfer to intact host blastocysts as these developed as chimaeric embryos to term.

Animals↗
PubMed1977

Evaluation of the technique of immunosurgery for the isolation of inner cell masses from mouse blastocysts.

Inner cell masses (ICMs) immunosurgically-isolated from 31/2-day mouse blastocysts were examined for trophoblast cell contamination and developmental capacity. Blastocysts were preincubated in rabbit anti-mouse antiserum, washed thoroughly and then incubated in complement. The ICMs were then easily dissected by drawing through a fine pipette. Various experiments confirmed that the trophectoderm had been completely removed by this treatment. Firstly, the ICMs did not bind a fluorescein-conjugated antibody directed against rabbit IgG, indicating the absence of cells exposed to the rabbit antiserum during the immunosurgical procedure. Secondly, ICMs dissected from blastocysts preincubated in a suspension of melanin granules did not include any of the trophoblast cells that had phagocytosed the granules. And, thirdly, the protein synthetic profile of these ICMs was similar to microsurgically dissected ICMs, and in particular, trophoblast specific spots were absent. The developmental capacity of immunosurgically-isolated ICMs was tested by injecting them into blastocysts and transferring to the uterus of 2 1/2-day pseudopregnant recipients. Extensive chimaerism was detected in the majority of implants, 5-6 days after transfer, but only in ICM-derived tissues. This demonstrates both the lack of trophoblast cell contamination and functional viability of these ICMs.

Animals↗
PubMed1977

Trophoblastic vesicles of preimplantation blastocysts can enter into quiescence in the absence of inner cell mass.

Preimplantation mouse blastocysts were dissected into inner cell mass (ICM) and trophoblast cells. These fragments were transferred to pseudo-pregnant mice which were left intact or ovariectomized. The latter group received progesterone to permit blastocysts and the dissected fragments to enter into quiescence, prior to injection of oestradiol to induce implantation. Trophoblastic vesicles, without ICM, entered into quiescence and implanted whereas the ICM did not. The entry of trophoblast into quiescence does not appear therefore to be governed by the ICM.

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