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Biomedical subjects

G Brem

Publications and source records attributed to G Brem.

At least 181 records · Page 10Linked to original sources
PubMed1991

A mammary-specific promoter directs expression of growth hormone not only to the mammary gland, but also to Bergman glia cells in transgenic mice.

The whey acidic protein (WAP) promoter has been previously used to target the expression of heterologous genes to the mammary glands of transgenic mice. To direct the expression of human GH (hGH) to mouse mammary glands, hGH-coding sequences have been coupled to WAP promoter sequences (WAP-hGH). Female transgenic mice carrying the WAP-hGH constructs show expression of hGH in the mammary gland, demonstrating the functionality of the transgenes. However, when other organs from these transgenic mice were examined, high level expression of hGH was unexpectedly observed in the brains of all male and female mice. Using in situ hybridization or immunohistochemistry, hGH expression from the transgene was seen to occur specifically in Bergman glia cells. In contrast, mice carrying hGH-coding sequences linked to the metallothionein promoter do not express hGH in these cells. Neither the endogenous WAP gene nor at least three other transgenes in which heterologous genes have been placed under the transcriptional control of the WAP promoter are expressed in the brain. Thus, we propose that the combination of the WAP promoter and the hGH structural gene results in a novel tissue specificity in the Bergman glia.

Animals↗
PubMed1991

Growth characteristics of metallothionein-human growth hormone transgenic mice as compared to mice selected for high eight-week body weight and unselected controls. I. Body weight gain and external body dimensions.

Body weight gain and external body dimensions of MT-hGH transgenic mice were compared with mice (NMRI) selected for high 8-week body weight (N8) and unselected controls derived from the NMRI strain (Pop). The growth curves from day 30 to 120 of transgenic mice exhibited a significantly steeper slope than those of male and female controls and of female N8 mice and did not show sex-related differences. The continuous pattern of GH secretion in transgenic mice is discussed as a possible reason for this phenomenon. Body weight gain of transgenic mice did not significantly exceed that of male N8 mice. None of the groups showed an obvious prolongation of the period of rapid daily weight gain. Maximum body weights of male and female transgenic mice were significantly higher than those of sex-matched controls but not of N8 mice. A drastic loss of body weight of about 25% of the maximum value was observed in the transgenic group prior to death. External body dimensions were largest in MT-hGH transgenic animals, followed by N8 mice and controls. In addition to these absolute measurements, values were related to the cube root of maximum body weight of the same animal. This is the first study that provides a comparative analysis of the effects of GH gene transfer and selection for body weight gain on body growth of mice derived from an outbred strain.

Animals↗
PubMed1991

Growth characteristics of metallothionein-human growth hormone transgenic mice as compared to mice selected for high eight-week body weight and unselected controls. II. Skeleton.

Growth hormone and mechanical loading are known to be important factors influencing bone growth. We have measured proportions of the skull and the postcranial skeleton of metallothionein-human growth hormone (MT-hGH) transgenic mice expressing high levels of hGH in their serum, of NMRI mice being large as a result of selection for high 8-week body weight (N8), and of unselected controls (Pop) derived from the NMRI strain. Absolute bony dimensions of transgenic mice were as a rule significantly larger than those of controls, the differences ranging between 3% and 32% in males and from 6% to 28% in females. By contrast, the enlargement of skeletal dimensions of N8 mice did not exceed 10% and was restricted to distinct bones. When related to the cube root of maximum body weight of the same animal, bones of controls were as a rule larger than those of N8 and MT-hGH transgenic mice. A detailed analysis of bony dimensions of GH transgenic mice and of mice selected for high body weight was carried out to judge the effects of GH overexpression and mechanical loading due to increased body weight on bone growth. The fact that bones of transgenics were as a rule larger than those of selected mice in spite of both groups reaching similar maximum body weights, suggests that skeletal gigantism in MT-hGH transgenic mice can only in part be a result of increased body weight.

Animals↗
PubMed1991

Expression of metallothionein-human growth hormone fusion genes in transgenic mice results in disproportionate skeletal gigantism.

Transgenic mice harbouring mouse metallothionein I-human growth hormone (MT-hGH) fusion genes were produced using the microinjection technique. The bones of adult MT-hGH transgenic mice, which continuously expressed high levels of hGH in their serum, and age-matched controls lacking detectable concentrations of hGH were measured microscopically. In addition to analyzing absolute skeletal dimensions, measurements were related to the cube root of the maximum body weight of the same animal. Absolute values obtained from transgenic mice were significantly higher than those obtained from controls for most of the defined measurements. However, the increase in skeletal dimensions was mostly not as pronounced as the increase in body weight and all bones were not affected to the same extent. There was no significant correlation between the serum GH concentration in individual mice and their degree of bony overgrowth. A disproportionate skeletal gigantism in MT-hGH transgenic mice may result from time differences in epiphyseal union of various bones of both sexes as well as differences in mechanical bone loading due to a drastically increased body weight. Individual concentrations of locally produced tissue insulin-like growth factor I (IGF I) might also play a role. Possible effects of these factors are discussed. The results presented in this study show that MT-hGH transgenic mice provide a powerful tool for the investigation of hormonal regulation of bone growth.

Amino Acid Sequence↗
PubMed1991

[Unexpected transgene expression of a mammary-specific growth hormone gene construct in Bergmann glial cells of the mouse].

Pronuclear microinjection was used to produce transgenic mice harboring gene constructs, in which 110 base pairs (WAP1) or 2.4 kilobases (WAP2) of the 5' flanking sequences of the whey acidic protein (WAP) gene were fused to human growth hormone (hGH)-coding sequences. Female WAP-hGH transgenic mice expressed the transgenes in the mammary gland, the expression of the WAP2-hGH transgene mirroring that of the endogenous WAP gene. When other organs were examined, high level expression of hGH was observed in the brains of WAP2-hGH transgenic mice. Using in situ hybridization and immunohistochemistry, hGH expression from the transgene was seen to occur specifically in Bergmann glia cells. While normally neither WAP nor hGH is expressed in this type of cell, it appears that a combination of the regulatory region of the WAP gene and the hGH structural gene results in a novel tissue specificity in Bergmann glia cells.

Animals↗
PubMed1991

[In vitro embryo production from oocytes from ovaries of a single slaughtered cow].

This communication describes the in vitro maturation and in vitro fertilization of bovine follicular oocytes. Further development of the embryos was achieved by using a granulosa cell culture system. The in vitro development of oocytes to morula/blastocyst stages obtained from individual cows was compared to the results of pooled simultaneous cultured oocytes and to our over-all results of this method. While there were no statistical differences in the developmental rates between these three groups (individual cows: 28.1%, simultaneous pool: 34.0%, over-all results: 32.7%) marked differences were found between the 22 animals investigated separately. These results indicate that there were great individual variabilities due to the oocyte population comparable to the variations in ovarian response to superovulation.

Animals↗
PubMed1990

[The reproductive function in experimentally-produced monozygotic twin bulls].

Reproductive functions were evaluated in 12 experimentally derived monozygotic cattle twins (6 pairs). In 4 twin pairs GnRH (20 micrograms Receptal i.m.) was administered in monthly intervals from 6 through 12 months of age. LH-secretion was determined by radioimmunoassay up to 6 hours after the GnRH-challenge in hourly collected peripheral blood samples. In 5 twin pairs (age 14 to 20 months) semen was collected 5 times and processed for cryoconservation. In fresh and in frozen-thawed semen samples sperm motility was determined by means of a computerized system. Twins showed a remarkable uniform response to the GnRH-challenge. One set of twins (HF-breed) had a significantly reduced response compared to the other pairs (DFV-breed). Both individuals of this particular pair had a low percentage of progressively motile spermatozoa. In pairs with physiological sperm motility, variance of this parameter within pairs and between pairs was not different. In contrast, twin uniformity concerning the average velocity of motile spermatozoa was high; differences between set of twins explained most of the total variance. According to this study, reproductive parameters in monozygotic cattle twins are strongly influenced by twin uniformity.

Animals↗
PubMed1990

Transgenic offspring by transcaryotic implantation of transgenic ovaries into normal mice.

Female transgenic mice may be unable to reproduce successfully if the product encoded by the transgene results in pathological changes or affects the fertility of the mouse. To approach this problem, we have produced chimaeras by transferring the ovaries of transgenic mice into normal mice of the same strain. Such chimaeras will be an ideal tool for investigating the interactions between transgenic ovaries and normal mice or vice versa. Here we show that, using this method, we were able to get large numbers of transgenic offspring even from founder transgenic female mice that were themselves infertile as a result of the overexpression of growth hormone genes. Although none of the ovary recipients were given immunosuppressant treatment, 60% of the recipients had biologically active ovaries over a mean period of about 100 days.

Animals↗
PubMed1990

naf, a trans-regulating negative-acting factor encoded within the mouse mammary tumor virus open reading frame region.

The mouse mammary tumor virus (MMTV) long terminal repeat (LTR) open reading frame (ORF) encodes a negative acting factor (naf). In our test system, naf mediates its effect in trans on another MMTV provirus in which the 5' LTR has been replaced by that of Rous sarcoma virus. naf effects are evidenced at the level of transcriptional initiation rather than as reduced mRNA stability. The introduction of a premature termination codon into the MMTV LTR-encoded ORF abolishes the transcriptional down regulation localizing naf within the ORF. In addition, sequences in the gag/pol genes between +320 and +646 and between +3626 and +4590 relative to the site of transcription initiation are also involved in the MMTV-mediated transcriptional down regulation.

Amino Acid Sequence↗
PubMed1990

Tissue concentration, mRNA expression and stimulation of IGF-I in luteal tissue during the oestrous cycle and pregnancy of cows.

The expression of IGF-I in bovine luteal tissue was demonstrated by parallel measurement of IGF-I tissue concentration and its mRNA; highest synthesis was observed during Days 12-17 of the cycle and the first months of pregnancy. Tissue levels of IGF-I increased from Days 1-5 to Days 12-17 of the cycle followed by a rapid decrease at luteolysis; there was a continuous decline from early pregnancy until Months 6-9. Microdialysis perfusion experiments with corpora lutea in vitro at Days 8-11 of the cycle revealed a major effect: release of progesterone and oxytocin were highly stimulated in a dose-dependent manner. We suggest that IGF-I could be important in regulating the function of the bovine corpus luteum and may act in an autocrine/paracrine way.

Animals↗
PubMed1990

HLA class-I-transgenic mice as model system to study MHC-restricted antigen recognition in man.

In order to develop a possible animal model to study HLA linked diseases of man, we established HLA-B27 transgenic mice (TGM). As aberrant and overexpression of MHC molecules can be toxic for cells, we aimed at obtaining a physiological expression of the human antigen and used a genomic 25kb Sal I fragment for embryo injection, coding for the HLA-B* 2705 heavy chain. Five independent founder mice were obtained containing varying copies of the fragment (1 to 10). RNA analysis from different tissues showed an expression pattern similar to endogenous H-2 class I genes. HLA-B27 antigen could be detected on lymphocytes derived from all five founder mice, even in the absence of human beta 2-microglobulin (hu beta 2m). It was found that the presence of hu beta 2m strongly enhances HLA-B27 cell surface expression in mice with few copies of the transgene, but was not necessary for efficient and high cell surface presentation in the 10 copy line. In all HLA-B27 TGM lines, the HLA molecule functions as restriction element in anti-viral responses. In addition, we could show that T lymphocytes of the transgenic animals respond to the same HLA-B27 restricted influenza peptide as is recognized by human influenza-specific, HLA-B27 restricted cytotoxic T cell lines.

Animals↗
PubMed1990

[Transgenic mice as disease models].

The methods used for making transgenic mice such as DNA microinjection in pronuclei, transformation of embryonic stem cells and production of chimeras, infection by retroviral vectors and sperm cells as carriers for foreign DNA are reported. Furthermore some characteristics of transgenic mice are mentioned, in particular factors influencing integration and expression of gene constructs. Different kinds of disease models using transgenic mice are available. This has been achieved by insertional mutagenesis, dominant negative mutations, changes caused by overexpression of transgenes, gene ablation, targeted mutation, and transfer of oncogenes. The importance of ongoing research in transgenic animals is emphasized.

Animals↗