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Biomedical subjects

J Grinsted

Publications and source records attributed to J Grinsted.

At least 55 records · Page 3Linked to original sources
PubMed1983

Growth pattern of the sex ducts in foetal mouse hermaphrodites.

In this report the morphology of the gonads and the growth of the Wolffian and Müllerian duct in foetal mouse true hermaphrodites (16 days p.c.) have been studied and compared to that of normal mice. The ducts from the hermaphrodites were placed in one of five groups according to the proportion of male and female characteristic of the gonad. When more than 85% of the gonadal tissue was masculine, the Wolffian ducts showed the same percentage of cells in mitosis (mitotic index, MI) as normal males. The MI of the Wolffian ducts was lower, but constant, if the gonad contained between 0 and 85% of testicular tissue. The number of Leydig cells in the gonads showed a linear relationship with the percentage of testicular tissue. Apparently, the MI of the Wolffian duct does not increase with increasing 'maleness' and with the number of Leydig cells. Four possibilities are put forward to explain the constant level of MI: (1) The Leydig cells of hermaphrodites may be deficient in producing testosterone. (2) The Leydig cells may produce testosterone at a normal rate but the epithelial cells of the Wolffian duct may not respond to increasing levels of testosterone by increasing their mitotic activity. (3) The presence of female gonadal tissue may directly or indirectly inhibit the mitotic activity of the epithelial cells of the Wolffian duct. (4) The epithelial cells of the Wolffian duct may respond to a low threshold level of testosterone, but maximal response is only triggered by a critical higher hormone level present only in group V. In hermaphrodites, the Wolffian duct attached to a gonad without testicular tissue and without Leydig cells, has a MI which is significantly to a gonad without testicular tissue and without Leydig cells, has a MI which is significantly higher than in normal females. It is suggested that circulating testosterone from the contralateral gonad is responsible for this high MI. In the Müllerian duct a mitotic index similar to that of the normal females was only found when the gonad contained from 0 to 15% of testicular tissue. If a gonad contained more than 15% of testicular tissue, the MI of the attached Müllerian duct was much lower equalizing that of normal males. No influence on the growth of the Müllerian duct could be observed from the contralateral gonad.

Animals↗
PubMed1982

Genetic and molecular characterization of Tn21, a multiple resistance transposon from R100.1.

Tge transposon Tn21 has been transposed from R100.1 to plasmid pACYC184 and, from the resulting recombinants, to plasmid R388. The sites of insertion and the orientation of the element in several pACYC184::Tn21 recombinants have been examined. Restriction enzyme analysis of these recombinants has resulted in a detailed map of Tn21; this is compared with the published maps of the relevant part of R100.1. Heteroduplex analysis has shown short inverted repeat sequences at the ends of the element. With various in vitro-generated deletion mutants of Tn21, the internal gene necessary for transposition (tnpA) was localized within the terminal 4.3 kilobases of the right-hand end of the element. Genetic analysis of transposition of Tn21 suggests that the process proceeds via cointegrates. Since the end products of transposition are simple recombinants of the element and the recipient replicon, Tn21 must contain a gene that codes for a resolvase type of activity (tnpR gene).

Conjugation, Genetic↗
PubMed1982

Influence of mesonephros on foetal and neonatal rabbit gonads. I. Sex-steroid release by the testis in vitro.

The experiments were performed to study the influence of mesonephros on gonadal sex hormone release. Foetal and neonatal rabbit testes were cultured for 5 days, with and without their mesonephric tissue. The culture media were harvested every day and analyzed by RIA for the content of testosterone, progesterone and oestradiol. The development of the tissues were evaluated microscopically after culturing. The results show that between day 20 pc and day 1 pp the mesonephric tissue lowered the amounts of testosterone in co-cultures with testis. This effect disappears when the mesonephric derived cells develop the capacity to synthesize a meiosis inducing substance (MIS). A relationship between decrease of testosterone and secretion of MIS is discussed. It is concluded that the steroid producing cells of the testis, the Leydig cells, originate or are heavily influenced by mesonephros during early testicular organogenesis.

Animals↗
PubMed1982

Influence of mesonephros on foetal and neonatal rabbit gonads. II. Sex-steroid release by the ovary in vitro.

To test whether the mesonephros influences the steroid hormone release by the foetal and neonatal ovary, rabbit ovaries were cultured with and without the mesonephros for a period of 5 days. The media were harvested once every day and analyzed by RIA for the content of testosterone, oestradiol and progesterone. Mesonephros produced progesterone only at day 20 pc. At day 21 and 28 pc significant amounts of all three hormones were produced. The media of the co-cultures of ovaries with the mesonephros contained on day 23 and 28 pc less testosterone. On day 23 pc less les and on day 3 pp more oestradiol was found in the media of the co-cultures. At day 21 pc progesterone release was increased by the mesonephros. It could be concluded that the mesonephros is able to synthetize steroids and possesses the capacity both to lower and to increase ovarian steroid release in culture. The enhancement of ovarian steroid synthesis in cocultures with the mesonephros at certain ages might be due either to increased substrate production and/or increased enzymatic activity. The lowering of steroids seen at different ages might be due to mesonephric steroid binding. The mesonephros appeared to influence the male and female rabbits differently at the same ages.

Animals↗
PubMed1981

Feminizing effect of mesonephros on cultured differentiating mouse gonads and ducts.

Gonads were removed from fetal mice at about the time that gonadal sex differentiation occurs. The gonads were cultured in vitro with or without their mesonephric tissue. When gonads and ducts removed from sexually undifferentiated fetuses were cultured together, the gonads of both sexes developed female characteristics, whereas gonads cultured without mesonephros developed according to the sex of the fetus from which they were removed. Gonads of sexually differentiated fetuses developed whether they were cultured with or without the mesonephros.

Animals↗
PubMed1981

Molecular nature of a plasmid specifying beta-lactamase production in Haemophilus ducreyi.

We characterized pJB1, the plasmid previously reported to mediate beta-lactamase production in Haemophilus ducreyi. We studied its relationship to pMR0360 and RSF0885, the plasmids responsible for beta-lactamase production in Neisseria gonorrhoeae and Haemophilus parainfluenzae, respectively. Although pJB1 was maintained as a multicopy pool in Escherichia coli, it was not stably maintained in the absence of antibiotic selection. Electron microscope heteroduplex studies showed that it carried 100% of the transposable ampicillin resistance sequence TnA. This sequence was transposed to plasmid pUB307 at a low rate. Heteroduplexes between pMR0360 and pJB1 showed that they contained 3.3 megadaltons of homologous sequences. Two sets of nonhomologous sequences, one a TnA sequence and the other a non-TnA sequence, took the form of insertion loops. For plasmids pMR0360 and RSF0885, previously shown to be highly related, the nonhomologous sequences took the form of a substitution loop. We concluded that all three plasmids shared major portions of their sequences but differed in discrete segments. pJB1 was the first such plasmid to have a physically and functionally intact TnA sequence.

Ampicillin↗
PubMed1981

Meiosis-inducing and meiosis-preventing substances in human male reproductive organs.

The initiation of meiosis is controlled by two substances, a meiosis-inducing substance (MIS) and a meiosis-preventing substance (MPS). These have been shown to be present in reproductive organs of both sexes of different mammals. In this investigation MIS and MPS were also shown to be present in man. MIS was found in fetal and adult epididymides and testes. MPS was obtained from the tests of one fetus, which was delivered by laparotomy. MPS could not be found in the testes of another fetus, which was aborted by prostaglandin F2 alpha and oxytocin. No or only weak MPS activity was detectable in the adult testis. This report indicates that continued spermatogenesis might be influenced by the MIS:MPS ratio. MPS was shown not to be species-specific. MIS and MPS activity have been evaluated by qualitative scoring of the different germ cell stages present in fetal gonads after culture in used media containing MIS or MPS.

Adult↗
PubMed1980

The EcoRI restriction endonuclease with bacteriophage lambda DNA. Kinetic studies.

The kinetics of the reactions of the EcoRI restriction endonuclease at individual recognition sites on the DNA from bacteriophage lambda were found to differ markedly from site to site. Under certain conditions of pH and ionic strength, the rates for the cleavage of the DNA were the same at each recognition site. But under altered experimental conditions, different reaction rates were observed at each recognition site. These results are consistent with a mechanism in which the kinetic stability of the complex between the enzyme and the recognition site on the DNA differs among the sites, due to the effect of interactions between the enzyme and DNA sequences surrounding each recognition site upon the transition state of the reaction. Reactions at individual sites on a DNA molecule containing more than one recognition site were found to be independent of each other, thus excluding the possibility of a processive mechanism for the EcoRI enzyme. The consequences of these observations are discussed with regard to both DNA-protein interactions and to the application of restriction enzymes in the study of the structure of DNA molecules.

Bacteriophage lambda↗
PubMed1980

Nucleotide sequences at the ends of the mercury resistance transposon, Tn501.

The nucleotide sequences at the ends of the mercury-resistance transposon, Tn501, have been determined. The terminal sequences are inverted repeated sequences 38 nucleotide pairs in length, which differ in 3 nucleotide pairs. The transposon is flanked by directly repeated sequences of 5 nucleotide pairs, originating from a single pentanucleotide sequence in the recipient replicon. There is no obvious homology between recipient replicons at the site of insertion of the transposon. The structures of the ends of Tn501 are compared with those of other transposons and insertion sequences. The use of Tn501 to locate an EcoRI site within a genetically defined sequence of interest is discussed.

Base Sequence↗
PubMed1980

Persistence and spread of a chloramphenicol resistance-mediating plasmid in antigenic types of Escherichia coli, pathogenic for piglets.

All chloramphenicol-resistant Escherichia coli strains isolated from piglets in the State veterinary Serum Laboratory, Copenhagen, in 1974-1975 harbored plasmids of IncFII group with largely the same resistance markers. Two strains from 1978 carried plasmids with similar characters. Restriction enzyme analysis of DNA from these plasmids with restriction endonucleases EcoRI, BglII, and PstI shows that the Cm plasmids are extremely closely related; but the patterns obtained (particularly from PstI digests) enable the classification of the plasmids into groups. These bear a strong relation to time and place of isolation so that plasmids isolated on the same farm belong to the same group even when their host strains are of different antigenic types. It is concluded that these plasmids have evolved from a single plasmid.

Animals↗
PubMed1980

Non-disjunction in trisomy 21: study of chromosomal heteromorphisms in 110 families.

QM variants on chromosome 21 and silver staining of NOR regions were applied in the study of non-disjunction in 110 families from different parts of Denmark. In 76% of the families the study was informative. Paternal failures were observed in 11% on Funen as compared 23.5% on Zealand. In one family, crossing-over on the short arms of chromosome 21 in the mother and mitotic non-disjunction of chromosome 21 was observed. Maternal first meiotic error predominates in both high maternal and low maternal age. Also in paternal non-disjunction failures of first meiotic division predominate. Two maternally and one paternally originated cases of de novo translocations were observed.

Adolescent↗
PubMed1980

New translocation sequence mediating tetracycline resistance found in Escherichia coli pathogenic for piglets.

A discrete piece of deoxyribonucleic acid coding for tetracycline (Tc) resistance was found to move from one R plasmid to another in an Escherichia coli strain which is pathogenic for piglets. Since this phenomenon took place also in rec strains, the Tc segment was classified as a transposon and called Tn804. Restriction enzyme analysis with EcoRI, BglII, and HindIII indicated that Tn804 is related to Tn10, a well-known transposon that codes for resistance to tetracycline. Hybridization between plasmids carrying the two transposons provided proof of homology between Tn10 and prt of Tn804. Electron microscopic studies showed a transposon-like structure composed of one loop-stem structure with inverted repetitions of approximately 0.9 megadaltons inserted into the loop of a second loop-stem structure. It is suggested that Tn804 is composed of Tn10 plus another transposable sequence.

Animals↗