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M I Sherman

Publications and source records attributed to M I Sherman.

At least 73 records · Page 4Linked to original sources
PubMed1978

Changes in the surface of the mouse blastocyst at implantation.

Implantation is a critical event, and perhaps the earliest one, in the maternal recognition of pregnancy. Information transfer from conceptus to mother might occur during, and subsequent to, implantation at the level of cell surface interaction. Therefore, attempts have been made both to identify the phases of implantation during which changes in the blastocyst surface occur and to characterized such changes. In vitro, blastocysts have been found to go through a series of discrete steps which are analogous to implantation in utero, and these steps can be retarded or prevented by the use of either suboptimal culture media or an inappropriate substratum. Morphological surface changes are not apparent when the blastocyst becomes adherent to the substratum; however, marked differences in blastocyst surface structure are revealed by scanning electron microscopy at the onset of trophoblast outgrowth. Studies at the molecular level implicate collagen as having a role in blastocyst adhesiveness, but other cell surface components are also likely to be involved.

Animals↗
PubMed1978

In vitro studies of mouse embryos bearing mutations in the T complex: t6.

Cultured blastocysts homozygous for the t6 mutation lose their inner cell mass within a few days of attachment to the culture dish. At about the same time it becomes apparent that putative t6-mutant trophoblast cells and their nuclei fail to enlarge to the degree of their normal counterparts. These abnormalities in mutant embryos are reflected by an abrupt drop on the seventh equivalent gestation day in the rate of increase of beta-glucuronidase activity. The failure of t6/t6 trophoblast nuclei to enlarge normally appears to be due partially to endoreduplication at a slower rate than normal trophoblast nuclei and partially to premature cessation of DNA synthesis. Analyses indicate that this abnormality is not reversed when mutant embryos are placed in chimeric association with normal ones. Trophoblast outgrowths from mutant and normal trophectodermal vesicles are similarly distinguishable by differences in outgrowth and nuclear size as well as DNA content and synthesis. Despite the fact that t6/t6 embryos and trophectodermal vesicles are phenotypically different from normals from early times in culture, the trophoblast cells in the mutant structures acquire and continue to produce two enzymes characteristic of trophoblast differentiation, delta 5, 3 beta-hydroxysteroid dehydrogenase and plasminogen activator. On the basis of these and previous observations, we propose that the primary effect of the t6 mutation is to cause a metabolic lesion which kills inner cell mass cells relatively quickly but which has a more gradual effect upon trophoblast cells. The fact that phenotypically recognizable t6/t6 trophoblast cells can survive for several days before dying makes this a potentially useful system in which to search for the t6 gene product(s).

Animals↗
PubMed1977

Nature of lethality of t mutations in embryos.

Mutations in the genes of the T complex in mice can lead to death at various stages of embryogenesis. It has been suggested that the T genes specify cell surface antigens which are essential for normal organisation of certain cells within the embryo. But, there is now evidence that at least some of these T complex mutations are simply generalised cell lethals.

Animals↗
PubMed1977

Histologic analyses of experimental tumors from mouse blastocyst-derived cell lines.

Previous work has shown that established cell lines can be derived from cultured mouse blastocysts. Although these cell lines differed from one another morphologically, immunologically, and biochemically, it has not been easy to determine what embryonic cell type (if any) each cell line represents. We showed in this report that these blastocyst-derived lines could produce tumors in syngeneic mice at low yields and presented the results of histologic analyses of the tumors which we carried out to learn more about the kinds of cells present in each of the lines. Tumors derived from cell line MB2 contained two kinds of cells. Most of the cells were similar to those found in so-called "parietal yolk sac carcinomas," secreted Reichert's membrane-like material, and could be found in subsequent transplant generations. The other cell type resembled trophoblast giant cells morphologically and did not survive transplantation. These results showed that MB2 contained cells which were either parietal endoderm cells or a closely related precursor. The tumor derived from MB4 consisted of small, closely packed cells intermixed with larger cells with foamy cytoplasm and occasional giant cells. Cells in subsequent passages of the tumor were often organized into acinar clusters. Biochemical evidence has suggested that MB4 cells resembled one or both components of visceral yolk sac. Visceral yolk sac sarcomas have not previously been reported; the MB4-derived tumor may prove to be the first. Tumors derived from line MB31 contained both fibroblastic and epithelioid cell types which could not be more definitively identified. Cultures derived from each kind of tumor in each case contained cells morphologically characteristic of those in the originally inoculated population. Our results showed that tumors produced from blastocyst-derived cell lines did not resemble the teratocarcinomas which formed when blastocysts were implanted into an ectopic site in vivo: They did not contain a wide variety of cell types, nor did they possess pluripotent embryonal carcinoma "stem" cells characteristic of the teratocarcinoma. That each blastocyst-derived line gave rise to a different kind of tumor suggested that each line may have been made up of cells "trapped" at some stage characteristic of the development of a particular embryonic or extraembryonic tissue. However, each tumor did contain at least two distinct cell types; this suggested that cells in the blastocyst-derived lines, though restricted to their developmental potential, may not yet have been completely determined.

Animals↗
PubMed1976

In vitro studies of mouse embryos bearing mutations at the T locus: tw5 and t12 .

Lethal mutations in the T region of chromosome 17 in the mouse cause death at specific stages of embryonic development. It is widely believed that death of homozygous mutant embryos occurs as a result of aberrant cell-cell interaction followed by disorganization and death of specific cell types within the embryo. In vitro culture of blastocysts homozygous for one of these mutations, tw5, has revealed that this mutation is lethal for all cells of the mutant embryo. In addition, measurements of beta-glucuronidase activity indicate that the lethal period of the tw5 mutation is the same in vitro as it is in vivo. Similar biochemical studies with t12 mutant embryos demonstrate that cessation of macromolecular synthesis occurs rather abruptly at the morula stage, the time at which those mutant embryos die in vivo. These results lead us to propose that all cells within the conceptus are directly and profoundly affected by early acting t mutations, and that failure of some cell types to organize properly is not an adequate explanation of the death of these mutants.

Animals↗
PubMed1976

Plasminogen activator in early embryogenesis: enzyme production by trophoblast and parietal endoderm.

We have surveyed the early stages in the development and differentiation of cultured mouse embryos for plasminogen activator production. This enzyme is first detectable by the sixth equivalent gestation day. Thereafter, cultured blastocysts produce plasminogen activator with a biphasic time course: in the first phase, enzyme secretion rises to a maximum at about the eighth day and then decreases; a second phase, during which more enzyme accumulates, begins somewhat later and continues to at least the fifteenth day. By fractionating the blastocyst into its constituent cell types, we have identified the trophoblast as the cells responsible for the first phase of enzyme synthesis. The pattern of enzyme production by the trophoblast is closely correlated with the invasive period of these cells in vivo and implies that plasminogen activator is involved in embryo implantation. The second phase of plasminogen activator production is due to parietal endoderm, which initiates enzyme synthesis upon differentiation from the inner cell mass. The properties of the parietal endoderm suggest that plasminogen activator may participate in the migration of these cells and/or in the metabolism of Reichert's membrane which accompanies embryo growth. These results are consistent with the concept, deveolped from work on other cell types, that plasminogen activator may represent a generalized mechanism for tissue remodeling and cell migration.

Animals↗
PubMed1976

Gonadotrophin stimulation of progesterone synthesis by midpregnancy mouse ovarian cells in vitro.

The ability of cultured midpregnancy mouse ovarian cells to synthesize progesterone de novo and from oxogenous pregnenolone has been assessed. The conversion of pregnenolone to progesterone is almost completely blocked by cyanoketone, a known inhibitor of delta5,3beta-hydroxysteroid dehydrogenase (3beta-HSD) activity, but is unaffected by aminoglutethimide, which inhibits the cholesterol side-chain cleavage enzyme complex (desmolase). Since there is little metabolism of the formed progesterone, the ability of ovarian cells to convert exogenous pregnenolone to progesterone in vitro reflects the activity of 3beta-HSD in these cells. Cultured ovarian cells are also capable of endogenous progesterone production in the absence of added pregnenolone, although the absolute amount of progesterone produced is considerably less than that produced from exogenous pregnenolone. Since endogenous progesterone accumulation is almost completely blocked by the addition of aminoglutethimide to the culture medium, it is concluded that this response does represent de novo progesterone synthesis. Neither bovine luteinizing hormone (LH) nor human chorionic gonadotrophin (hCG) affects 3beta-HSD activity in cultured ovarian cells. The ability of the cells to secrete or to further metabolize the progesterone formed is also unaffected. However, both LH and hCG stimulate endogenous progesterone production within one hour of their addition to the culture medium. The stimulation, 2-10 fold in several experiments, can be maintained for at least six days of culture, and is not a result of an increase in the growth rate of the ovarian cells. As would be expected, the stimulation is blocked by the addition of aminoglutethimide to the culture medium. Taken together, these facts suggest that gonadotrophic hormones stimulate progesterone production by ovarian cells specifically by their action at steps prior to the conversion of pregnenolone to progesterone.

Aminoglutethimide↗
PubMed1976

Differentiation of early mouse embryonic and teratocarcinoma cells in vitro: plasminogen activator production.

Cultured mouse blastocysts produce plasminogen activator, a protease that converts the zymogen plasminogen into the trypsin-like enzyme, plasmin. We have fractionated the blastocyst and cultured the constituent cell types. Trophoblast outgrowths free of inner cell mass derivatives secrete plasminogen activator during a time period that closely parallels the invasive phase of trophoblast cells in utero. Isolated inner cell masses also produce plasminogen activator; further fractionation of the inner cell mass as well as studies with primary cultures obtained from midgestation tissues demonstrate that enzyme formation is restricted entirely to parietal endoderm cells. Secretion of the enzyme may facilitate the migration of parietal endoderm cells along the trophoblast layer as the yolk sac cavity enlarges during gestation. F9 embryonal carcinoma cells do not secrete detectable amounts of plasminogen activator. However, when these cells are induced to differentiate, the resulting parietal endoderm-like cells are capable of producing the enzyme. These results are consistent with previous findings suggesting that plasminogen activator production may be a characteristic of invasive and/or migratory cells.

Blastocyst↗
PubMed1975

Long term culture of cells derived from mouse blastocysts.

The development of mouse blastocysts in primary culture has been followed for up to two months. The trophectoderm layer of the blastocyst gives rise to a monolayer of trophoblast cells; cells resembling both ectoplacental cone cells and primary giant cells are observed. The former can transform to giant cells, presumably secondary trophoblast, after several days in culture. Giant trophoblast cells are evident in the culture for much longer than the normal gestation period. Under the culture conditions described, the proportion of blastocysts showing substantial inner cell mass (ICM) proliferation in vitro is higher than that noted in previous studies. The ICM clumps develop into either egg cylinder-like structures, or, more commonly, into spherical, fluid-filled vesicles. The vesicles, which resemble yolk sac morphologically and biochemically [10, 11], continue to enlarge in size during several weeks of culture. The vesicles are attached to the underlying trophoblast monolayers by a stalk. Cells appear to migrate from this stalk out along the culture dish. The result after two to four weeks of culture is the appearance of a mixed monolayer containing a variety of different cell types. Secondary cultures of blastocyst cells have been continuously maintained in vitro for more than one year. Four lines of cells, all developing from the same pool of blastocysts, have been monitored for morphological, growth and biochemical properties, as well as chromosome number. Each line contained two or more morphologically distinct cell types, clearly indicated by cloning studies after eight months of culture. Doubling times and saturation densities among the four lines differed, as did biochemical properties. Although none of the cell lines resembled trophoblast biochemically after 7.5 months in culture, one line, MB4, possessed a number of biochemical properties in common with midgestation yolk sac. After a further five months of culture, some enzymes in the four lines were relatively unchanged; in other cases, notably with alkaline phosphatase, a sharp drop in enzyme activity was observed. One cell line, MB2, and specifically one of the cell types in this line, produced a yellow-orange pigment with a spectrum resembling that of a heme protein. After 7.5 months of culture, two of the four lines, MB21 and MB31, contained large numbers of cells with a diploid number of chromosomes. However, by 12.5 months in culture, the large majority of metaphases in all four cell lines possessed a hypotetraploid chromosome number. In a number of studies carried out to date, none of the cell lines generated tumors when injected into syngeneic hosts.

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