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Biomedical subjects

M Monk

Publications and source records attributed to M Monk.

At least 37 records · Page 2Linked to original sources
PubMed1988

Sexing of preimplantation mouse embryos by measurement of X-linked gene dosage in a single blastomere.

Single blastomeres were isolated from zona-free 8-cell mouse embryos and assayed for X-linked hypoxanthine phosphoribosyl transferase (HPRT) activity and autosome-linked adenine phosphoribosyl transferase (APRT) activity. At this stage of development both X chromosomes are active in female embryos. Hence, a bimodal distribution of HPRT: APRT ratios, corresponding to male (XY) and female (XX) biopsied samples, was observed due to the 2-fold difference in gene dosage for HPRT activity. Batches of putative male and female embryos identified in this way were transferred to pseudopregnant recipient females. Development of the seven-eighths embryos was equivalent to that of control zona-free intact embryos. Sex determination by measurement of X-linked gene dosage was accurate and rapid enough to allow transfer of embryos of known sex without the need for cryopreservation.

Adenine Phosphoribosyltransferase↗
PubMed1987

Preimplantation diagnosis of deficiency of hypoxanthine phosphoribosyl transferase in a mouse model for Lesch-Nyhan syndrome.

Male mice embryos deficient in hypoxanthine phosphoribosyl transferase (HPRT), derived from heterozygous (carrier) females and normal males, were diagnosed by biochemical microassay of HPRT activity in a single cell isolated from the eight-cell preimplantation embryo. The sampled embryos were transferred to recipient mothers and examined on the 14th day of gestation to confirm the accuracy of the preimplantation diagnosis. The diagnosis was sufficiently rapid that freezing of the embryos before transfer was not necessary. Of the embryos diagnosed as HPRT negative all 4 that grew into fetuses were correctly identified as HPRT-deficient males.

Animals↗
PubMed1987

Temporal and regional changes in DNA methylation in the embryonic, extraembryonic and germ cell lineages during mouse embryo development.

This paper shows stage- and tissue-specific global demethylation and remethylation occurring during embryonic development. The egg genome is strikingly undermethylated and the sperm genome relatively methylated. Following a loss of genomic methylation during preimplantation development, embryonic and extraembryonic lineages are progressively and independently methylated to different final extents. Methylation continues postgastrulation and hence could be a mechanism initiating, or confirming, differential programming in the definitive germ layers. It is proposed that much of the methylation observed in somatic tissues acts to stabilize and reinforce prior events that regulate the activity of specific genes, chromosome domains or the X chromosome (in females). Fetal germ cell DNA is markedly undermethylated and we favour the idea that the germ lineage is set aside before the occurrence of extensive methylation of DNA in fetal precursor cells.

Animals↗
PubMed1985

Differences in methylation on the active and inactive human X chromosomes.

Methylation of CCGG sites was examined in four regions of the X chromosome with four X-chromosome clones, three obtained by cloning random segments and one encoding a structural gene. In DNA from human peripheral blood cells unmethylated sites correlating with the inactive X chromosome were detected in the vicinity of two of the random clones and also in the vicinity of a cloned sequence of the X-linked phosphoglycerate kinase gene (PGK). The third random clone covered a region whose methylation pattern was unchanged between the active and inactive X chromosomes. Differential methylation at the sites detected appears to have no functional role in the maintenance of the inactive X chromosome since both active and inactive X chromosomes were found to be undermethylated in DNA from human lymphoblastoid cells.

Base Sequence↗
PubMed1985

Dog and cat ownership among suicides and matched controls.

In Washington County, Maryland, ownership of cats and/or dogs was compared among 48 residents who committed suicide in the years 1975-83 and 96 living controls matched to the suicides by race, sex, and date of birth. Another comparison used as controls persons of same race, sex, and age who died of causes other than suicide in the same year as the suicide. No material association between pet ownership and suicide was observed.

Adolescent↗
PubMed1978

Problems in suicide statistics for whites and blacks.

The accuracy of suicide statistics was assessed by comparing published Health Department suicide rates for an area of New York City with Medical Examiner records. For the period 1968--1979, records from the Medical Examiner's Office were searched to determine all deaths classified as definite suicides. Another group of deaths was considered suicide by the Medical Examiner but never classified as such. These deaths we labeled "assigned suicides." When definite suicides were compared with all deaths considered suicide by the Medical Examiner (definite and assigned suicides), black suicide was underestimated by 80 per cent and white suicide by 42 per cent. Underestimation was the same for males and females but varied by age group. In 1968, when the seventh revision of the International Classification of Deaths (ICD) was used, Health Department suicide rates for blacks were almost identical to Medical Examiner rates, while white rates were underestimated by 25 per cent. In 1969--1970, when the eighth revision was used, Health Department statistics underestimated black suicides by 82 per cent and white suicides by 66 per cent. Reasons for the underestimations were related to the methods used in committing suicide by the two ethnic groups and to the ways that suicide classification has changed from the seventh to eighth revision. Implications for research using official death certificate reports are discussed.

Adolescent↗
PubMed1978

X-chromosome activity in preimplantation mouse embryos from XX and XO mothers.

Embryos from XO female mice begin development with half the activity levels of an enzyme (HPRT) coded for by a gene on the X chromosome, compared with embryos from XX females. Groups of unfertilized eggs and individual embryos at the 8-cell, morula and blastocyst stages were assayed for HPRT activity. An autosomally coded enzyme (APRT) was assayed simultaneously in the same reaction mix as a control. There is a substantial increase in HPRT activity by the 8-cell stage. However, the mean activity of HPRT in embryos of XO mothers remains half that in embryos of XX mothers. This suggests a significant maternally inherited component of HPRT activity in 8-cell embryos. By the 9- to 16-cell morula stage the HPRT activities in the two groups of embryos become similar due, presumably, to a transition to embryo-coded activity; HPRT activities in individual morulae from XX mothers show a bimodal distribution consistent with the hypothesis that both X-chromosomes are active in XX embryos at this stage.

Adenine Phosphoribosyltransferase↗
PubMed1976

Patterns of lactic dehydrogenase isozymes in mouse embryos over the implantation period in vivo and in vitro.

Following blastocyst implantation, or outgrowth in vitro, the LDH isozyme pattern changes from that of the maternally inherited B subunit isozyme form (LDH-1) to a pattern dominated by A subunits (Auerbach & Brinster, 1967, 1968). In preimplantation embryos we have observed additional isozyme bands, as yet unidentified. An analysis of the pattern of newly synthesized LDH isozymes and specific activity of LDH in different regions of early postimplantation embryos suggests that there is a sequantial activation of A and B subunits, and that activity first appears in ICM- (inner cell mass) derived tissues and then in trophoblast-derived tissues. In vitro, in the absence of ICM cells, the transition of LDH-isozyme pattern does not occur in outgrowing trophoblast giant cells. This suggests a possible inductive interaction between ICM and trophoblast.

Animals↗
PubMed1975

The kinetics of derepression of prophage lambda following ultraviolet irradiation of lysogenic cells.

Double lysogens for prophages lambda cI+ and lambda cI ind-ts-857 are induced only by the combined effects of ultraviolet (UV) irradiation and high temperature, not by either treatment alone (Sussman and Jacob, 1962). We have followed the kinetics of inactivation of the cI+ repressor brought about by irradiation in asynchronously and synchronously growing cultures of B/r (lambda cI ind- ts-857). Assays of the yield of phage released as a result of temporary thermal inactivation of the UV-resistant ind- ts-857 repressor at intervals after the irradiation accurately reflect the time course of UV-induced inactivation of the cI+ repressor. The results show that UV-induced derepression takes place in all cells of the population approximately 20 min after the irradiation whether the cells were growing asynchronously or synchronously. Hence UV induction of prophage lambda is not triggered at a particular stage in the cell cycle.

Cell Count↗