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M A Surani

Publications and source records attributed to M A Surani.

17 recordsLinked to original sources
PubMed1992

Parental imprinting: potentially active chromatin of the repressed maternal allele of the mouse insulin-like growth factor II (Igf2) gene.

The mouse insulin-like growth factor II (Igf2) gene, which is located on distal chromosome 7 (Chr7), has been shown previously to undergo tissue-specific parental imprinting. This imprinting results in expression of Igf2 from the paternally inherited chromosome and repression of the maternally inherited allele in most tissues of the developing embryo. We are using embryos with the maternal duplication and paternal deficiency of distal Chr7 to characterize the mechanism that underlies repression of the maternal allele. We show that the chromatin of the 5' region of the repressed Igf2 allele is potentially active for transcription rather than heterochromatic. In particular, a CpG island that comprises one of the two strong promoters is unmethylated at both parental alleles, and DNase I hypersensitive sites in and around the strong promoters are consistently present on both parental chromosomes. In agreement with the chromatin state, primary transcripts from the maternal Igf2 allele have been detected at low but significant levels. These findings differ from observations in other instances of imprinting, namely, X-chromosome inactivation and transgene imprinting in mice. Although no parent-specific differences were detected in either DNA methylation or sensitivity to nucleases at these promoters, we have observed parental methylation differences in a region several kilobases upstream of the first exon. The differential activity of the parental Igf2 alleles could be achieved through epigenetic modifications situated outside the promoters or by subtle and yet unidentified modifications at the promoters.

Alleles↗
PubMed1979

Glycoprotein synthesis and inhibition of glycosylation by tunicamycin in preimplantation mouse embryos: compaction and trophoblast adhesion.

The synthesis of glycoproteins and inhibition of protein glycosylation by tunicamycin were examined during development of preimplantation mouse embryos and trophoblast adhesion. Tunicamycin specifically inhibits glycosylation of asparaginyl residues of glycoproteins. Tunicamycin, 0.25-5.0 microgram/ml, had no effect on early cleavage or aggregation between embryos, but the embryos remained irreversibly uncompacted when control embryos developed to the blastocyst stage. Trophoblast adhesion and giant cell outgrowth were reversibly inhibited and the binding of Con A was also reduced. Incorporation of 3H-mannose into blastocysts was inhibited by 80%, but that of 3H-glucosamine and 3H-leucine by only 28 and 18%, respectively, in the presence of 1.0 microgram/ml tunicamycin. Qualitative analysis showed that the incorporation of the sugars was markedly reduced in the majority of the fractions, but the synthesis of these carbohydrate-deficient glycopeptides was essentially normal. However, protein-polysaccharide fractions with nearly 40% of the incorporated glucosamine and only 5% mannose and 1% leucine were insensitive to inhibition by tunicamycin. Membrane-bound N-glycosidically linked glycoproteins therefore evidently play an important role during compaction and in trophoblast adhesion of mouse embryos.

Animals↗
PubMed1979

Affinity of uterine luminal proteins for rat blastocysts.

The binding of 125I-labelled rat uterine luminal proteins from Day-5 pregnant rats showed higher binding affinity to blastocysts than did the binding of proteins in uterine fluid from pro-oestrous rats (Day 0), rat serum albumin (RSA) or bovine serum albumin (BSA). Apparently little uptake of proteins into cells by phagocytosis or entry into the blastocoelic cavity occurred since similar results were obtained in the presence of sodium azide or cytochalasin B. Autoradiographic studies showed that the proteins were localized on the outer surface of the blastocyst. The binding was Ca2+-dependent. Denaturation of Day-5 uterine proteins at 80 degrees C reduced the counts to the values obtained with undenatured RSA and Day-0 fluids; this residual binding was considered as non-specific. The binding of labelled Day-5 uterine proteins was substantially reduced in the presence of unlabelled Day-5 proteins but to a lesser extent in the presence of RSA or rat serum. The dissociation of the bound labelled Day-5 uterine proteins occurred most rapidly in the presence of unlabelled Day-5 proteins. However, dissociation occurred within 2 h in the presence of other macromolecules, suggesting that the binding was not strong.

Animals↗
PubMed1977

Response of preimplantation rat blastocysts in vitro to extracellular uterine luminal components, serum and hormones.

The influence of extracellular environmental factors on preimplantation rat blastocysts was tested by determining the number of embryos which escaped from their zonae pellucidae, followed by attachment and outgrowth of trophoblast giant cells, after 72 h in culture Uterine luminal ocmponents from individual females, or hormones, were included in Dulbecco's medium which contained 4 mg/ml bovine serum albumin. In about 20% of cases, uterine fluids were embryotonic. However, uterine fluids from day-5 pregnant females, the day of implantation in the rat, were more potent in these tests than uterine fluids obtained from ovariectomized females treated with progesterone alone. The potency of a mixture of the 2 fluids was also high. Uterine fluids obtained at 14 h after an injection of oestradiol and progesterone to the ovariectomized females, were also effective in these tests. Rat serum and foetal calf serum were effective too, but steroids or insulin alone in the medium had no detectable influence on embryos. Serum or uterine luminal proteins appear to be essential for maintaining the viability of the blastocysts and for inducing the responses observed here. In the uterine fluids, some proteins released into the lumen after treatment of females with oestradiol and progesterone appear to be the biologically active components. Differences in the responses of blastocysts in vitro are compared with those in vivo.

Animals↗
PubMed1977

Qualitative and quantitative examination of the proteins of rat uterine luminal fluid during pro-oestrus and pregnancy and comparison with those of serum.

Rat serum and uterine luminal proteins at two distinct endocrinological stages were analyzed electrophoretically. The quantitative relationships between the major macromolecular fractions were calculated from the densitometer scans. At pro-oestrus there was a marked increase in the total luminal proteins which was probably not due to transudation of serum into the lumen because of the presence of large amounts of two proteins, of approximate mol. wt 125,000 and 130,000, which were not detected in serum. Quantitative estimates of proteins of different molecular weight fractions in the fluids showed that there were considerable differences between the three fluids, indicating that the hormones do not merely induce a free passage of serum proteins into the lumen. On Day 5 of pregnancy there was a considerable lower amount of protein in the uterine lumen and qualitatively these proteins differed from those in serum and the uterine lumen at pro-oestrus.

Animals↗
PubMed1977

Radiolabelled rat uterine luminal proteins and their regulation by oestradiol and progesterone.

Radiolabelled uterine luminal proteins were obtained 6 h after instillation of 5--10 muCi [35S]methionine into the lumen of each uterine horn of rats. The proteins were analysed electrophoretically on 6% polyacrylamide gels and incorporation of the precursor into the separated proteins was estimated in 0-18 cm gel slices by scintillation spectrometry. Major incorporation was obtained on Day 5 of pregnancy in a group of proteins of approximate mol. wt 3 X 10(4), 4-5 X 10(4) and 5-5 X 10(4) and in proteins of mol. wt 8--10 X 10(4). During pro-oestrus, substantial incorporation of the precursor occurred in a group of protein of mol, wt 13-5 X 10(4), 12-5 X 10(4) and 7-5--8-0 X 10(4) and slight incorporation in proteins of mol. wt 4-5 X 10(4). These changes were mimicked in ovariectomized females by injections of appropriate steroids: progesterone and oestradiol were necessary to induce the proteins detected during pregnancy, oestradiol alone was able to reproduce the changes observed at pro-oestrus. The proteins in the lumen appear to be of uterine origin because radiolabelled serum proteins were not detected in the lumen after an i.p. injection of the isotope. Also, labelled proteins were detected in the horn receiving the isotope but not in the contralateral horn injected with saline. Cycloheximide, given i.p. simultaneously with the isotope but not in the contralateral horn injected with saline. Cycloheximide, given i.p. simultaneously with the isotope, suppressed synthesis of uterine proteins.

Animals↗
PubMed1977

Effect of dibutyryl cyclic AMP and oestradiol on incorporation of [3H]leucine into the proteins of luminal fluid of the rat uterus.

An injection of 12-5 nmol dibutyryl cyclic AMP (dbcAMP) into each uterine horn of ovariectomized rats maintained on progesterone alone, enhanced incorporation of [3H]leucine into uterine luminal proteins. A value of 11-73 X 10(3) c.p.m. [3H]leucine incorporated/rat was found after injection of dbcAMP compared with 3-69 X 10(3) c.p.m./rat after injection of saline. An injection of 1-0 microgram oestradiol, in contrast, gave 58-05 X 10(3) c.p.m./rat. Electrophoretic analysis showed that the radioactively labelled proteins found after an injection of dbcAMP or oestradiol were qualitatively similar to those detected on day 5 of pregnancy, the day of blastocyst implantation. The nucleotide thus apparently elicits a uterine response similar to that observed after an injection of oestradiol.

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.

Animals↗
PubMed1976

Uterine luminal proteins at the time of implantation in rats.

Changes in rat urerine luminal proteins were analysed during pregnancy and after ovariectomy on Day 3 of pregnancy plus daily administration of progesterone, when delay of implantation is imposed. Total protein levels reached a peak level on Day 5 of pregnancy, the day of implantation, in the intact but not the ovariectomized females. Qualitative analyses of protein-SDS complexes showed an increase in a protein of molecular weight of approximately 70.000 and others of higher molecular weight during pregnancy, but in ovariectomized females the proteins of higher molecular weight were virtually undetectable by Day 10. The entry of blastocysts into quiescence after ovariectomy appears to be an adaptation by the embryos to suboptimal uterine luminal conditions.

Animals↗
PubMed1975

Hormonal regulation of proteins in the uterine secretion of ovariectomized rats and the implications for implantation and embryonic diapause.

Uterine secretions were obtained from long-term ovariectomized rats given progesterone for 10 days followed by oestrogen and progesterone. Analysis of the protein content was carried out using polyacrylamide disc gel electrophoresis at pH8-9 AND ALSO OF THE PROTEIN-SODIUM DODECYL SULPHATE COMPLEXES. When progesterone was given alone, there was a lack of high molecular weight proteins. When oestradiol was also given, a protein (mol. wt 70,000) was detected within 1 hr. At 13 to 20 hr after oestrogen, there was a shift towards the secretion of high molecular weight proteins when the secretion profiles were similar to those of normal pregnant animals at Day 5, the day of implantation in the rat. The hormonal regulation of the secretion proteins is discussed. The physiological aspects of implantation in terms of zona lysis, embryonic diapause and the release from diapause after oestrogen treatment are discussed with reference to the changes in the intraluminal proteins.

Albumins↗
PubMed1975

Zona pellucida denudation, blastocyst proliferation and attachment in the rat.

The mode of zona pellucida denudation and blastocyst proliferation and attachment was investigated in Wistar rats during day 5 of pregnancy and in ovariectomized pregnant animals given 5-0 mg progesterone daily until the 10th day, when 0-2 mug oestradiol was injected together with progesterone. During day 5 of pregnancy, when only 5 empty zonae were detected from 32 animals, zona denudation occurred by lysis, which took 6 h. Zona denudation occurred by shedding in the ovariectomized pregnant animals; 190 empty zonae were detected from 40 animals. Oestradiol administration to the experimental animals caused lysis of the shed zonae 24-30 h after oestradiol treatment. Air-dried preparations of the embryos showed that the blastomeres proliferated exponentially from a mean of 27-52 +/- 4-0 cells per embryo at 12.00 h on day 5 of pregnancy to 53-96 %/- 2-58 cells per embryo at 22.00 h, with a cell doubling time of 10 h in normal animals. In the ovariectomized animals, blastocysts were arrested at about the 100-cell stage on the 10th day. Oestradiol administration to the experimental animals did not induce mitosis; the embryos implanted without further cell division. The number of free embryos recovered declined from a mean of 12-0 per animal at 12.00 h to 4-25 per animal at 22.00 h on day 5 of pregnancy. The number of embryos recovered from the ovariectomized animals varied between one and 11 per animal. The results show that cell division continued in embryos within ovariectomized pregnant animals in the absence of oestrogen, until about the 100-cell stage. There was no further cell division before nidation when oestradiol was administered. The empty zonae were, however, lysed between 24 and 30 h after oestradiol treatment. The zona lytic factor appears to be oestradiol dependent and of maternal origin. A causal relationship exists between zona lysis and embryo attachment, which is independent of the number of cells per blastocyst.

Animals↗
PubMedDate not supplied

Factors affecting cellular mosaicism in the expression of a lacZ transgene in two-cell stage mouse embryos.

In the present study, we have analysed the expression pattern of a lacZ transgene (CMZ12) in preimplantation stage mouse embryos. The transgene is expressed at the two-cell stage, where it shows cellular mosaicism due to variable expressivity. The variable gene expression indicates a partial penetrance of the transgene. The extent of variation in expression is influenced by the genetic background of the oocyte. DBA/2 and CFLP genetic backgrounds promote high expression of the transgene, while Balb/c, C57BL/6, DDK, and F1 (C57BL/6 x CBA) genetic backgrounds give none or very little lacZ activity. In vitro culture of one-cell embryos to the two-cell stage induces the expression of lacZ in all strain backgrounds tested. The variation in CMZ12 expression is a transient phenomenon and does not affect later stage activity of the transgene. Nuclear transfer experiments and DNA methylation analysis suggests that a heritable modification of the transgene locus has not occurred.

Animals↗