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Biomedical subjects

J Grinsted

Publications and source records attributed to J Grinsted.

At least 73 records · Page 4Linked to original sources
PubMed1980

Temperature measurements of rabbit antral follicles.

The temperature of 40 antral follicles in 16 rabbits was measured by microthermoelectrodes and by thermovision during anaesthesia. The temperature in the follicles was 2.8 +/- 0.2 degree C lower than the core body temperature and 1.4 +/- 0.2 degree C lower than in the ovarian stroma. No differences were observed between the temperatures obtained from large and small antral follicles, and different conditions of measurement gave similar results.

Animals↗
PubMed1979

The reactions of the EcoRi and other restriction endonucleases.

The reaction of the EcoRI restriction endonuclease was studied with both the plasmid pMB9 and DNA from bacteriophage lambda as the substrates. With both circular and linear DNA molecules, the only reaction catalysed by the EcoRI restriction endonuclease was the hydrolysis of the phosphodiester bond within one strand of the recognition site on the DNA duplex. The cleavage of both strands of the duplex was achieved only after two independent reactions, each involving a single-strand scission. The reactivity of the enzyme for single-strand scissions was the same for both the first and the second cleavage within its recognition site. No differences were observed between the mechanism of action on supercoiled and linear DNA substrates. Other restriction endonucleases were tested against plasmid pMB9. The HindIII restriction endonuclease cleaved DNA in the same manner as the EcoRI enzyme. However, in contrast with EcoRI, the Sa/I and the BamHI restriction endonucleases appeared to cleave both strands of the DNA duplex almost simultaneously. The function of symmetrical DNA sequences and the conformation of the DNA involved in these DNA--protein interactions are discussed in the light of these observations. The fact that the same reactions were observed on both supercoiled and linear DNA substrates implies that these interactions do not involve the unwinding of the duplex before catalysis.

Coliphages↗
PubMed1979

Induction of meiosis in fetal mouse testis in vitro by rete testis tissue from pubertal mice and bulls.

To test whether a meiosis-inducing substance (MIS) is responsible for the induction of meiosis in the testis at puberty, pubertal mouse rete testis was grown with (1) fetal undifferentiated mouse testis attached to the other side of a filter and (2) the used medium obtained from culture of the rete testis of a pubertal bull for 2 days. In both systems meiosis was induced in the fetal testis showing that MIS is not species specific. No meiosis-preventing effect was seen and it is concluded that meiosis in the testis is triggered at puberty as a result of the activity of the MIS concomitant with decreased activity of the meiosis-preventing substance.

Animals↗
PubMed1979

Sites of insertion of TnA and TnM in RP1 and its derivatives.

The sites of insertion of TnM into the plasmid RP1, into derivatives of RP1 lacking TnA, and into derivatives in which the location of TnA within RP1 has been altered, were determined. Similarly, the sites of insertion of TnA into derivatives of RP1 from which TnA had been deleted, both with and without copies of TnM, have been examined. These studies show the presence in the plasmids of 'hot-spots' for TnA and TnM insertion. It is clear from the observations, however, that a particular DNA sequence in the recipient replicon is not sufficient to definite a 'hot-spot' since particular sequences sometimes do, and sometimes do not, contain many sites of insertion for a given transposon.

Base Sequence↗
PubMed1978

Regional preference of insertion of Tn501 and Tn802 into RP1 and its derivatives.

The sites of insertion of Tn501 into RP1 and into derivatives of this plasmid that either lack the Tn801 (TnA) element or contain it in a different location have been determined. Similarly, the sites of insertion of Tn802 into a derivative of RP1 that lacks the Tn801 element and into recombinants of this plasmid with Tn501 were determined. 'Hot spots' for insertion were observed with both transposons; but it is clear that a particular DNA sequence is not sufficient to define a 'hot spot', since a particular region does contain many insertions when present in one plasmid but does not do so when part of another.

Base Sequence↗
PubMed1978

The stable carriage of two TnA units on a single replicon.

Bacterial plasmids which contain a copy on TnA are refactory to the uptake of a second by transposition. However plasmids containing two such copies can be constructed by in vitro recombination techniques. Some plasmids containing two copies of TnA have been obtained by conventional transposition, but in all cases they arose by the virtually simultaneous insertion of both units into a replicon that carried no TnA. All stable plamids containing two copies of TnA carried the transposons in opposite orientation.

DNA Replication↗
PubMed1978

Follicular growth in fetal and prepubertal ovaries of humans and other primates.

Follicular growth begins in the fetal ovary as soon as the first follicles are formed. Although orderly follicular growth is found in the fetal ovary, many of the early growing follicles show abnormalties. Follicles with irregular granulosa layers, with hypertrophied or with underdeveloped theca layers, are characteristic. Such follicles are rarely seen after birth. The ovary during childhood is an active organ in which follicular growth and follicular atresia normally take place. Follicles begin to grow at all ages, differentiate to preantral and antral follicles, but degenerate at various stages of their development before they reach pre-ovulatory sizes. Follicular growth in the fetus and children is dependent on hormones. Fetal gonadotrophins are necessary to ensure normal and sequential follicular growth before birth. During childhood a close correlation between follicle growth, hormone response and hormone production seems to exist. Certain diseases and treatment with cytotoxic agents or radiation to the abdomen influence ovarian development and follicular growth. Chromosome abnormalities, especially Turner's syndrome, trisomy 18 or 21, alter normal ovarian development by reducing the pool of available follicles and inhibiting follicular growth. Treatment with cytotoxic drugs inhibits follicular growth, while abdominal irradiation in childhood unless the ovaries are adequately shielded causes permanent damage by destroying the small follicles.

Abdominal Neoplasms↗
PubMed1977

Transposition of TnA does not generate deletions.

We have examined the incidence of loss of the TnA unit, Tn801, from RP1 under conditions where transposition of Tn801 to another replicon. R388, was readily detected. We found that the frequency of transposition of Tn801 from RP1 to R388 exceeded, by at least a factor of one hundred, the frequency at which it was deleted from RP1. We conclude that, in general, transposition of Tn801 does not generate derivatives of the donor plasmid which specifically lack Tn801. The relevance of these findings to the mechanism of transposition is discussed.

Chromosome Aberrations↗
PubMed1976

R-plasmid transfer in vivo in the absence of antibiotic selection pressure.

The persistence of an O18 Escherichia coli strain resistant to tetracycline, streptomycin, and sulfonamide has been followed in the fecal flora of a single individual over a period of 9 months. The strain in question carrying an R plasmid was detectable from the beginning of the survey, but it was only after a 10-day period of tetracycline therapy that it reached an all but permanent dominance in the fecal flora. No transfer of the R plasmid carried by the strain to any other coliform could be detected for 202 days after the end of tetracycline treatment. At this point, however, an O88 E. coli carrying the same plasmid as the O18 strain appeared briefly as a predominant component of the flora. The two plasmids isolated from the O18 and the O88 E. coli strains have been characterized in molecular terms and found to be similar. This suggests that R-plasmid transfer between two E. coli strains occurred in an individual who was living a normal daily life and who was not receiving antibiotics.

Anti-Bacterial Agents↗
PubMed1976

Properties of pGC1, a lac plasmid orginating in Yersinia enterocolitica 842.

pGC1, a self-transmissible lac plasmid that originated in Yersinia enterocolitica 842, is described. This plasmid is freely transmissible between strains of Y. enterocolitica and from such strains to strains of Escherichia coli. The plasmid can also be transferref among G. coli strains and back to Y. enterocolitica, although at a greatly reduced frequency. pGC1 has a molecular weight of about 33.0 x 10(6), has a base composition of about 44 mol% guanine plus cytosine, and is fi-.

Conjugation, Genetic↗
PubMed1976

Acceptance and transfer of R-factor RP1 by members of the "herbicola" group of the genus Erwinia.

The R-factor RP1 was transferred by conjugation from Pseudomonas aeruginosa PAO12r(RPI) to various strains of Erwinia herbicola and to one strain of Erwinia stewartii. The exconjugate strains had minimum inhibitory concentration values for carbenicillin, kanamycin, neomycin, and tetracycline somewhat lower than the corresponding values for the pseudomonad RP1 donor strain. The biochemical characteristics of the exconjugant strains displayed minor variation in some instances from those of the corresponding R- strains. Sensitivity of the RP1+ strains to the RP1-specific bacteriophages PRD1 and PRR1 varied from an efficiency of plating [compared with P. aeruginosa PA067(RP1)] of 0 [E. herbicola Y46(RP1)] to 133 [E. herbicola Y190(RP1)] and 148 [E. stewartii SS104R(RP1)] for PRD1, and from 0 [E. herbicola Y46(RP1)] to 0.0002 [E. herbicola Y185(RP1)] and 18.4 [E. stewartii SS104R(RP1)] for PRR1. The phage-resistant strain E. herbicola Y46(RP1), would donate, by conjugation, the R-factor to E. herbicola Y46rifr, P, aeruginosa PAT900, or Escherichia coli UB1005 only at extremely low frequencies, if at all. Transformation of E. coli JC7620 by covalently closed circular DNA from E. herbicola Y46(RP1) gave and E. coli R+ strain exhibiting the expected antibiotic resistance pattern and having the ability to donate RP1 by conjugation. It is suggested (i) that some strains of E. herbicola RP1 either do not produce RP1 pili or produce defective pili, and (ii) that sensitivity to the bacteriophages PRD1 and PRR1 is not a suitable means of diagnosing the presence RP1 in E. herbicola strains.

Bacteriophages↗