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Free access

Margarita M Ivanova, Brandie N Radde, Jieun Son, Fabiola F Mehta, Sang-Hyuk Chung and Carolyn M Klinge

Nuclear respiratory factor-1 (NRF-1) stimulates the transcription of nuclear-encoded genes that regulate mitochondrial (mt) genome transcription and biogenesis. We reported that estradiol (E2) and 4-hydroxytamoxifen (4-OHT) stimulate NRF-1 transcription in an estrogen receptor α (ERα)- and ERβ-dependent manner in human breast cancer cells. The aim of this study was to determine whether E2 and 4-OHT increase NRF-1 in vivo. Here, we report that E2 and 4-OHT increase NRF-1 expression in mammary gland (MG) and uterus of ovariectomized C57BL/6 mice in a time-dependent manner. E2 increased NRF-1 protein in the uterus and MG; however, in MG, 4-OHT increased Nrf1 mRNA but not protein. Chromatin immunoprecipitation assays revealed increased in vivo recruitment of ERα to the Nrf1 promoter and intron 3 in MG and uterus 6 h after E2 and 4-OHT treatment, commensurate with increased NRF-1 expression. E2- and 4-OHT-induced increases in NRF-1 and its target genes Tfam, Tfb1m, and Tfb2m were coordinated in MG but not in uterus due to uterine-selective inhibition of the expression of the NRF-1 coactivators Ppargc1a and Ppargc1b by E2 and 4-OHT. E2 transiently increased NRF-1 and PGC-1α nuclear staining while reducing PGC-1α in uterus. E2, not 4-OHT, activates mt biogenesis in MG and uterus in a time-dependent manner. E2 increased mt outer membrane Tomm40 protein levels in MG and uterus whereas 4-OHT increased Tomm40 only in uterus. These data support the hypothesis of tissue-selective regulation of NRF-1 and its downstream targets by E2 and 4-OHT in vivo.

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C. Collet, R. Joseph and K. Nicholas

ABSTRACT

Analysis of the tammar wallaby β-lactoglobulin cDNA and inferred amino acid sequences reveal extensive sequence divergence from the eutherian β-lactoglobulins. Conserved residues include the cysteines and a number of individual amino acids involved in structure and ligand-binding. The only region of extended similarity is a heptapeptide sequence which may impart specificity to its interaction with a receptor protein. Northern analysis of total mammary RNA revealed two transcripts which result from differential utilization of polyadenylation signals. The concentration of β-lactoglobulin mRNA increased in late lactation and correlates with increases in milk production and levels of milk fat. Quantification of β-lactoglobulin mRNA levels in hormone-stimulated mammary gland explants from tammars in late pregnancy suggests that maximal induction of the gene is dependent on prolactin alone and that expression is not modulated by other hormones known to play a role in the initiation of lactation in eutherians.

Free access

T Kimura, F Saji, K Nishimori, K Ogita, H Nakamura, M Koyama and Y Murata

The oxytocin receptor belongs to the G-protein-coupled seven transmembrane receptor superfamily. Its main physiological role is regulating the contraction of uterine smooth muscle at parturition and the ejection of milk from the lactating breast. Oxytocin receptor expression is observed not only in the myometrium and mammary gland but also in the endometrium, decidua, ovary, testis, epididymis, vas deferens, thymus, heart and kidney, as well as in the brain. The expression profile shows a tissue-specific as well as a stage-specific pattern. The oxytocin receptor gene is a single-copy gene consisting of four exons and three introns, localized at 3p25-3p26.2 in the human chromosome. In transfection studies using a fusion construct containing the promoter region of the oxytocin receptor gene inserted in a reporter plasmid, neither proinflammatory cytokines nor oestrogen directly activate the gene. The nuclear fractions from up-regulated (term myometrium) and down-regulated (non-pregnant myometrium) tIssues show differential patterns of protein binding to the 5'-flanking region, and a human homologue of chicken MafF has been cloned as a term-myometrium-specific oxytocin receptor modulator. The oxytocin receptor gene appears to be highly methylated. Methylation around intron 1 and in intron 3 might contribute to tIssue-specific suppression of the gene. The oxytocin receptor is also regulated by desensitization, whose mechanism appears to involve loss of ligand-binding activity of the protein as well as suppression of the oxytocin receptor mRNA transcription. These findings taken together indicate that the oxytocin receptor is regulated in a very complicated manner, and the transcriptional regulatory elements critical for this regulation should be investigated further.

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T. S. Tiong, J. L. Stevenson and A. C. Herington

ABSTRACT

The nature and tissue distribution of prolactin receptor (PRL-R) mRNA in both male and female rats was studied. A single mRNA species of 2.2kb was identified in the liver, kidney, adrenal, prostate, lactating mammary gland and ovary but not in the male lung, heart, skeletal muscle, thymus, adipose tissue or brain. There were distinct and contrasting sex differences in abundance of PRL-R mRNA in some tissues: liver (female>>male), kidney and adrenal (male >>female). A mRNA species of 4kb was occasionally detected in the male adrenal and female liver. Given previous reports on the effects of thyroid status on PRL binding, the effects of thyroxine (T4), propylthiouracil (PTU) or combined treatment on PRL-R mRNA were assessed. In the male rat, PTU treatment markedly increased (three- to fourfold) PRL-R mRNA in the liver but decreased it (∼50%) in the kidney. These changes were reflected in similar changes in lactogenic binding activity. T4 or PTU treatment increased PRL-R mRNA in the prostate, with no obvious changes in binding. No major changes were seen in adrenal glands. In the female rat, PTU had little effect on PRL-R mRNA in any tissue, although binding of 125I-labelled lactogen was decreased in both the liver and kidney. There was an unexpected threefold rise in PRL-R mRNA in the female kidney following combined T4 and PTU treatment. Overall, there was a quite close correlation between the effects of thyroid status on PRL-R mRNA levels and specific lactogenic binding to membranes prepared from the same tissue samples. These studies provide data on the tissue distribution and size of PRL-R mRNA in rats and suggest a novel and complex tissue- and sex-dependent regulation by thyroid hormone.

Free access

KJ Simpson, P Bird, D Shaw and K Nicholas

A 17.5 kDa protein was isolated from porcine whey by reverse phase HPLC and identified as a putative whey acidic protein (WAP) homologue by sequencing 35 and 40 amino acid residues of the amino- and carboxy-terminus respectively. Degenerate oligonucleotides to both of these amino acid sequences were designed and used in reverse transcriptase PCR with RNA from lactating porcine mammary gland as a template. A 162 bp PCR fragment was detected and sequenced. Compilation of the deduced and determined amino acid sequence revealed a protein of 111 amino acids, which had approximately 75, 50, 40 and 35% similarity at amino acid level to camel, rabbit, rat and mouse WAP respectively. It also included the four-disulphide core characteristic of all WAP proteins and most Kunitz-type protease inhibitors. This provides the first unequivocal evidence for WAP secretion in the pig. SDS PAGE analysis of the whey fraction showed that WAP is secreted as a major protein in sow's milk from farrowing to weaning. The molecular mass of WAP in SDS PAGE was significantly greater than the 11.7 kDa determined from amino acid sequence, indicating that porcine WAP is possibly glycosylated. Northern analysis detected a single mRNA transcript of approximately 600 bp in porcine RNA from the mammary gland of lactating sows. To examine the hormone-regulated expression of the WAP gene the mammary glands of sows at day 90 of pregnancy were biopsied and explants cultured for 3 days in the presence of various combinations of porcine insulin (I), cortisol (F) and porcine prolactin (P). Northern analysis of RNA extracted from the tissue indicated that WAP gene expression was barely detectable in the mammary gland prior to culture and there was no increment in explants cultured in the presence of I and F. However, a significant increase in the accumulation of WAP mRNA was observed in explants cultured in I, F and P. A similar result was observed for beta-casein and alpha-lactalbumin gene expression.

Free access

M Shimada, Y Yamashita, J Ito, T Okazaki, K Kawahata and M Nishibori

The present study aimed to investigate progesterone receptor (PR) gene expression in cumulus cells and their roles during meiotic resumption of porcine oocytes. The amount of PR-A or PR-B mRNA was analyzed by RT-PCR using primer sets for the PR-B region or the PR-A/B common region. The level of PR-B mRNA in cumulus cells was up-regulated by FSH and LH during the first 8 h of cultivation but the level significantly decreased at 12 h. However, a high level of total PR mRNA was maintained up to a cultivation period of 20 h. The level of PR-B protein in cumulus cells reached its maximum at 4 to 12 h, whereas PR-A predominated in cumulus cells of cumulus-oocyte complexes (COCs) at 20 h. Accompanying the shift in expression of PR isoforms, progesterone production in cumulus cells was significantly increased, and both the proliferative activity of cumulus cells during a 10- to 20-h cultivation period and the level of connexin-43, a major component of the gap junction, in cumulus cells significantly decreased. When COCs were cultured with FSH and LH for 10 h and then further cultured with additional RU486, there was a significant suppression in the shift in PR isoforms and in progesterone production, a loss of proliferative activity, and a decrease in connexin-43 mRNA in cumulus cells. Moreover, treatment with RU486 after 10-h cultivation of COCs inhibited the meiotic resumption of oocytes and cumulus cell expansion. These results suggest that the induction of PR isoforms in cumulus cells and their binding to progesterone appear to impact on proliferation and differentiation in a time-dependent manner, and the shift from PR-B to PR-A may help mediate certain events.

Free access

T Muller, M Simoni, E Pekel, CM Luetjens, R Chandolia, F Amato, RJ Norman and J Gromoll

The pituitary gonadotrophins LH and FSH are responsible for regulation of gametogenesis in the testis and ovary. Chorionic gonadotrophin (CG), a third closely related glycoprotein hormone derived by gene duplication of the LHbeta gene and secreted by the placenta in primates, is essential for the rescue of the corpus luteum and maintenance of pregnancy. We have recently shown that marmoset (m) CGbeta mRNA is highly expressed in the pituitary of the common marmoset (Callithrix jacchus) and that LH is less active than human CG in activating the human LH receptor lacking exon 10. To investigate further which gonadotrophin is the actual ligand of the LH receptor (LHR) of the marmoset monkey that naturally lacks exon 10, we identified and characterised the genomic organisation of the mLHbeta gene and its expression. Intergenic PCR amplification of the region encompassing the mLHbeta and the mCGbeta genes revealed that, surprisingly, mCGbeta is located 20 kbp upstream of the LHbeta gene, whereas in other species the intergenic distance is approximately 2-3 kbp. Sequence analysis of the mLHbeta coding region showed 70% identity to mCGbeta and 90% identity to human LHbeta at the amino acid level. Both gonadotrophin beta subunits are present at the genomic level, but RT-PCR of pituitary and placental total RNA using specific oligonucleotides for mCGbeta and mLHbeta showed high expression of mCGbeta mRNA in both tissues, whereas LHbeta was expressed neither in the pituitary nor in the placenta. Thus mLHbeta mRNA is lacking in the marmoset pituitary. Immunohistochemistry of marmoset pituitaries showed that mCG was confined to the gonadotrophes, and partly co-localised in cells stained positively for FSH. Western blot analysis confirmed the presence of mCG in the pituitary. Northern blot analysis using mCGbeta as a probe displayed one transcript of 0.7 kb in the pituitary and detected two transcripts of 1.1 kb and 2 kb in the marmoset placenta. Our results suggest that, in the common marmoset, CG is the only gonadotrophin with luteinising function that is present in the pituitary. We postulate that, owing to an unknown mutational event in evolution, expression of mLH was completely abolished, and CG - which, unlike LH, acts normally even when exon 10 is missing from the LHR - took over its function.

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F. F. Bolander and M. E. Blackstone

ABSTRACT

A radioimmunoassay was developed and validated for the major glycoprotein (gp58) of the mouse mammary tumour virus (MMTV). Using this assay, the expression of gp58 during pregnancy and lactation was found to parallel that for MMTV RNA. In particular, there was a very rapid induction in late pregnancy and a decline in late lactation, although some residual expression persisted well into involution. In cultures of normal mouse mammary tissue, induction of gp58 occurred after a 24-h lag period and began to reach a plateau after 3 days. Both the insulin and prolactin dose—response curves for gp58 resembled those for MMTV RNA; in contrast, the effects of steroid hormones on gp58 and MMTV RNA were disparate. Although progesterone stimulated the RNA, it only slightly increased gp58 levels; however, the presence of cortisol greatly augmented this stimulation, despite the inability of cortisol to induce RNA at physiological concentrations. These results suggest that insulin, prolactin and progesterone act primarily at the level of RNA accumulation in normal mammary epithelium, while cortisol affects some more distal event.

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C. Collet, R. Joseph and K. Nicholas

ABSTRACT

Two marsupial casein genes have been isolated from a tammar wallaby (Macropus eugenii) mammary gland cDNA library. Comparisons of the tammar α- and β-casein genes with their eutherian homologues reveal extensive divergence at the levels of nucleotide and amino acid sequences. Regions of similarity between the tammar and eutherian Ca2+-sensitive caseins are restricted to the major phosphorylation sites and the signal peptides. Quantification of casein mRNA levels in hormone-stimulated mammary gland explants from tammars in late pregnancy suggests that maximal induction of the β-casein gene is dependent upon prolactin and insulin, while maximal induction of the α-casein gene is dependent upon prolactin, insulin and cortisol. These results are in contrast to earlier studies which show that the maximal induction of a putative 19 kDa casein, α-lactalbumin and β-lactoglobulin in the tammar mammary gland is dependent upon prolactin alone. The expression of the latter three genes is not modulated by other hormones known to play a role in the in-vitro initiation of lactation in eutherians.

Free access

D J Flint, M Boutinaud, C B A Whitelaw, G J Allan and A F Kolb

Insulin-like growth factor-binding protein 5 (IGFBP-5) mediates involution of the mammary gland. The decrease in DNA content and mammary gland weight which accompanies involution was inhibited by prolactin (PRL) in wild-type but not transgenic mice expressing IGFBP-5. Phospho-STAT5 protein levels were significantly lower in IGFBP-5 transgenic mice during lactation suggesting that IGFBP-5 antagonises PRL signalling in the mammary epithelium. In contrast, phospho-STAT3 levels increased during involution to a similar extent in both wild-type and transgenic mice and were unaffected by PRL. PRL inhibited gene expression of matrix metalloproteinases (MMPs) 3 and 12 but not tissue plasminogen activator or plasmin in wild-type and transgenic animals. The effects of PRL on MMPs appear to be indirect since PRL failed to inhibit MMP-3, -7 or -12 expression in HC-11 cells or in a co-transfection including an activated PRL receptor, STAT5 and a MMP-3-luciferase reporter gene. PRL is a potent inhibitor, both of cell death, an effect which is suppressed by IGFBP-5, and of MMP expression, which is independent of the actions of IGFBP-5.