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G Morel

Publications and source records attributed to G Morel.

At least 73 records · Page 4Linked to original sources
PubMed1994

Ultrastructural expression of prolactin receptor in rat liver.

Prolactin (PRL) is a trophic hormone which acts mainly at the plasma membrane level of hepatocyte. The mechanisms involved in the transduction of the signal after binding of PRL to its receptors are not yet well documented. In the present study we have examined the subcellular patterns of PRL receptor expression in rat liver by ultrastructural in situ hybridization and immunocytology. In situ hybridization was performed using digoxigenin-labeled oligonucleotide probes revealed by indirect immunogold reaction. The expression of both the long and short forms of PRL-receptor mRNA was readily identified in the cytoplasmic matrix, and in association with the endoplasmic reticulum, but a low expression of these forms was detected in the nucleus of hepatocyte. Moreover, this expression appeared clearly higher in female rather than in male hepatocytes. On the other hand, immunogold detection of PRL-receptor protein was performed using two monoclonal antibodies (U5 and T6), specific to the extracellular domain of the PRL-receptor. Indirect immunocytological detection confirmed the presence of PRL receptor-like immunoreactivity at the level of the plasma membrane, and in the cytoplasmic matrix associated or not with endocytotic vesicles, the endoplasmic reticulum, the peroxisomes, the Golgi complex, and the nuclei of both male and female hepatocytes. No clear difference was found between U5 and T6 mAbs, with regard to the subcellular localization. These results show the distribution of both PRL-receptor mRNA and PRL receptor protein in numerous subcellular compartments of hepatocyte, and evidence that these compartments are involved in the early stage of the PRL action.

Animals↗
PubMed1994

Visualization of gene expression of short and long forms of prolactin receptor in rat digestive tissues.

Several effects of prolactin have been characterized in various tissues of the gastrointestinal tract. In the present study, the expression of short and long forms of prolactin receptor was explored and quantified in the digestive tract and correlated to the prolactin specific functions. Sections of all digestive tissues were analyzed by in situ hybridization, using 35S-labeled oligoprobes unique to each form of receptor. Macroautoradiogram signals were quantified and expressed in arbitrary units. In rat liver, prolactin receptor mRNAs are expressed to a much greater degree in females than in males. The short-form transcript is significantly expressed to a greater degree in liver, whereas the long form predominates in the pancreas and esophagus. In the remainder of the gastrointestinal tract, there is an equivalent distribution of short- and long-form transcripts. Relatively high signal intensities are seen in the stomach, duodenum, jejunum, ileum, and colon, whereas the rectum is essentially negative. The identification of prolactin receptor gene expression to limited regions should help establish specific functions associated with this hormone in the digestive tissues.

Animals↗
PubMed1994

Prolactin receptor immunoreactivity in rat anterior pituitary.

Prolactin (PRL) receptors have been identified in both classical and nonclassical target organs. Actions of PRL on the secretion of anterior pituitary hormones have been reported. In order to confirm the presence of PRL receptors on specific cell types of the anterior pituitary, immunocytology on ultrathin frozen sections was carried out using monoclonal antibodies specific to the rat PRL receptor. Anterior pituitary glands were removed and fixed in 4% paraformaldehyde or 2.5% glutaraldehyde and postfixed in 1% osmium tetroxide. Tissues were frozen and ultrathin sections were made by cryoultramicrotomy. In anterior pituitary cells, all endocrine cell populations showed PRL-R-like immunoreactivity. The relative labeling frequency based on immunolabeling studies was somatotrophs > lactotrophs > thyrotrophs approximately corticotrophs > gonadotrophs. Within all endocrine cell types, no apparent differences could be observed in the subcellular localization of PRL-R-like immunoreactivity. At the subcellular level, gold particles, either isolated or in groups of two, were seen at the level of the plasma membrane, in the cytoplasmic matrix, in the vicinity of the endoplasmic reticulum and in the nucleus. The identification of receptors specific to PRL within different cells of the anterior pituitary raises the interesting possibility that PRL may act via an autocrine or paracrine network in regulating anterior pituitary function.

Animals↗
PubMed1994

Growth hormone receptor binding protein in rat anterior pituitary.

GH is synthesized by the somatotrophs in the pituitary, where it may have paracrine actions. In order to identify the GH target cells in rat pituitary, the cellular distributions of rat GH receptor binding protein messenger ribonucleic acid (rGH-RBP mRNA) and protein were investigated at the electronmicroscopic level, using in situ hybridization and immunocytology, respectively, on ultrathin frozen sections of rat pituitary. Ultrastructural distribution of 125I-bGH, 30 min after intracardiac administration was also performed in order to determine the pituitary cell types that bind the labeled hormone. In situ hybridization was performed using digoxigenin-labeled oligonucleotide probe revealed by indirect immunogold reaction. rGH-RBP mRNA was readily identified in the cytoplasmic matrix, associated with the endoplasmic reticulum and the nucleus of the somatotrophs, the lactotrophs and the gonadotrophs. No significant signal was detected in the corticotrophs or thyrotrophs. The number of gold particles in each pituitary cell type was estimated by direct counting, and was compared to the results of hybridization performed on rat liver sections as a control. The results showed that the level of rGH-RBP mRNA was higher in hepatocytes than in the pituitary cells, and was higher in the somatotrophs and lactotrophs than in the gonadotrophs. Immunocytological detection of rGH-RBP was performed using two monoclonal antibodies (mAbs 43 and 263) directed against independent epitopes of the extracellular domain of the rGH-R. Indirect immunocytological detection showed regionalization of rGH-RBP; it was present in the cytoplasmic matrix and the nucleus of the hepatocytes and in discrete pituitary cells: somatotrophs, lactotrophs and gonadotrophs, but not in thyrotrophs or corticotrophs. Gold particle number was also higher in somatotrophs and lactotrophs than in gonadotrophs and higher in the nucleus compared to the cytoplasmic matrix. Radioiodinated GH was uptaken 30 min after injection by the same three pituitary cell types, showing evidence for the functional role of the GH receptor. In conclusion, we find that the cellular localization of rGH-RBP mRNA and protein is similar in discrete cell subpopulations of the pituitary, suggesting a direct effect of GH on somatotrophs, lactotrophs and gonadotrophs, through paracrine, autocrine or intracrine mechanisms.

Animals↗
PubMed1994

Intracellular gonadotropin-releasing hormone immunoreactivity in gonadotrophs of intact or castrated male rats: semiquantitative estimation of testosterone and GnRH antagonist treatment.

Changes in intracellular gonadotropin-releasing hormone (GnRH) immunoreactivity (GnRH-IR) in pituitary gonadotrophs were assessed by the use of a semiquantitative immunocytochemical method in male rats undergoing various manipulations known to greatly modify gonadotropin secretion. In basal conditions, immunoreactive GnRH was localized in the cytoplasmic matrix, the secretory granules and the nucleus of these cells. Following intravenous stimulation with GnRH (100 ng i.v.), the GnRH-IR increased rapidly in all these three subcellular compartments, peaking at 15 min. In untreated, long-term castrated rats, GnRH-IR increased both in the basal state and after administration of GnRH. Injection of the castrated rats with testosterone propionate reduced the observed GnRH-IR to the level observed in intact rats. Acute or chronic treatment of castrated rats with a potent GnRH antagonist rendered GnRH-IR completely undetectable in all the three previously positive subcellular compartments of gonadotrophs, and GnRH-IR did not reappear after stimulation with GnRH. In sum, the fact that modifications of GnRH immunoreactivity are observed in rat gonadotrophs: (1) confirms the GnRH internalization process; (2) suggests different sites of action for GnRH within the cell, and (3) demonstrates rapid clearance of intracellular GnRH after stimulation.

Animals↗
PubMed1994

Expression of the growth hormone receptor gene in human digestive tissue.

We have examined the forms and the distribution of the messenger ribonucleic acids (mRNAs) encoding the GH receptor (GHR) in human digestive tissues. GHR mRNAs were identified and characterized by Northern blot, dot blot, and in situ hybridization analyses, using complementary DNAs coding for the extracellular part of the human liver GHR. Amplification using the polymerase chain reaction was also used, as tissues express low levels of GHR mRNAs. Our results demonstrate that the GHR gene is expressed in human liver, pancreas, esophagus, stomach, small intestine, and colon. A single 4.5-kilobase mRNA form, which probably encodes the full-length membrane receptor, was detected. GHR mRNA was visualized by in situ hybridization in hepatocytes, exocrine pancreas, and some islet cells; signal was also present in the mucosa of the digestive tract. No specific GH-binding-protein mRNA was found, suggesting that in man, the soluble form of the receptor is generated through proteolytic cleavage of the membrane receptor.

Adolescent↗
PubMed1994

Signal transduction by the growth hormone receptor.

It has been proposed that dimerization of identical receptor subunits by growth hormone (GH) is the mechanism of signal transduction across the cell membrane. We present here data with analogs of porcine GH (pGH), with GH receptors (GHR) mutated in the dimerization domain and with monoclonal antibodies to the GHR which indicate that dimerization is necessary but not sufficient for transduction. We also report nuclear uptake of GH both in vivo and in vitro, along with nuclear localization of the receptor and GH-binding protein (GHBP). This suggests that GH acts directly at the nucleus, and one possible target for this action is a rapid increase in transcription of C/EBP delta seen in 3T3-F442A cells in response to GH. This tyrosine kinase-dependent event may be an archetype for induction of other immediate early gene transcription factors which then interact to determine the programming of the subsequent transcriptional response to GH.

Animals↗
PubMed1993

Evidence for a direct effect of growth hormone on osteoblasts.

In order to determine whether growth hormone (GH) exerts a direct effect on osteoblasts, in vitro and in vivo immunocytological studies were carried out on newborn rat calvaria and a clonal osteoblast-like cell line (MC3T3-E1) isolated from newborn mouse calvaria. After exposure to human growth hormone (hGH) or 1,25 dihydroxyvitamin D3 (1,25(OH)2D3), a significant increase in alkaline phosphatase activity was observed in MC3T3-E1 cells. Simultaneous exposure of MC3T3-E1 cells to hGH and 10 nM 1,25(OH)2D3 showed a synergistic effect of the two hormones on this activity. The optimal dose of hGH was 0.1 nM. An immunocytological procedure was performed on ultrathin frozen sections from 7-day-old rat calvaria and MC3T3-E1 cells cultured with hGH. GH-like immunoreactivity was observed in both cases. In calvaria, endogenous GH-like immunoreactivity was localized at the same ultrastructural level (plasma membrane, cytoplasmic and nuclear matrices) as exogenous GH-like immunoreactivity in MC3T3-E1 cells. Following the initial step of binding to the plasma membrane, GH may be internalized in the cytoplasmic matrix and nucleus. In situ hybridization revealed the presence of mRNA coding for GH receptor in calvaria cells. The density of these receptors seemed to be lower in osteoblasts than in hepatocytes. In MC3T3-E1 cells, hGH induced a dose-dependent secretion of insulin-like growth factor 1. In conclusion, these results indicate that GH may act directly on osteoblasts.

Alkaline Phosphatase↗
PubMed1993

Visualization of gene expression of short and long forms of prolactin receptor in rat reproductive tissues.

Prolactin receptor gene expression was visualized in various tissues by in situ hybridization. Probes specific to the intracellular domains of the short and long form of receptor were prepared. The specificity of these signals was controlled by competition with excess unlabeled homologous probes or heterologous probes; moreover, some tissues, such as penis and vagina, show no expression of either form of receptor mRNA. Macroautoradiogram signals (optical density) were quantified and expressed in arbitrary units. The long form of receptor mRNA was preferentially expressed in testis, epididymis, prostate, seminal vesicle, and mammary gland from lactating animals, whereas the expression of the two forms of mRNA was equivalent in ovary, uterus, and pregnant mammary gland. Signals were also localized at the light microscopic level to individual cells. This approach has permitted the precise localization of prolactin receptor mRNAs in reproductive tissues. Actions of prolactin have not been demonstrated in all tissues expressing receptor transcripts; thus it will be interesting to correlate the expression of long and short forms of receptor with specific functions.

Animals↗
PubMed1993

Orthodontic treatment needs in Westmead Hospital Dental Clinical School.

One hundred and fifty-four adolescents, 76 female and 78 male consented to take part in this survey. The two authors examined and assessed them for dental aesthetics, malocclusion related features and TMJ related signs. The patients were also questioned about their opinion of dental aesthetics, their interest in having orthodontic treatment and their TMJ symptoms. Only 63 per cent of the adolescents who were considered suitable for orthodontic treatment expressed an interest in wanting treatment. Twenty-seven per cent of patients had signs and/or symptoms of TMJ disturbance. No association was found between individual malocclusion problems and TMJ signs and symptoms. The authors considered 56.5 per cent of the total group for orthodontic treatment, the majority for aesthetic reasons, and placed them into high, medium and low priority groups. Fixed appliance therapy for both arches was the recommended type of treatment for most patients.

Adolescent↗
PubMed1993

Visualization of gene expression of short and long forms of prolactin receptor in the rat.

PRL receptor gene expression was visualized in various tissues by in situ hybridization, using 35S-labeled probes unique to each form of receptor. Tissues were removed rapidly from adult male and female rats and placed in liquid nitrogen. Cryostat sections (10 microns) were prepared, fixed, pretreated, and dehydrated before incubation with the various probes. Hybridization was performed overnight, after which the slides were first exposed to autoradiographic film and then dipped in nuclear emulsion and exposed for 1-2 weeks. The specificity of the signal was studied by competition and using radiolabeled heterologous probes. Some tissues show no expression of either form of receptor mRNA, such as olfactory bulb and penis. Macroautoradiogram signals (optical density) were compared to a standard curve to observe the variation in mRNA expression, which was expressed in arbitrary units. Sex differences in the expression of PRL receptors were seen in a number of tissues, such as adrenal gland and pituitary. Expression of mRNAs specific to the long form of PRL receptor was predominant in adrenal gland, pituitary, thymus, spleen, skin, heart, and skeletal muscle, whereas the short form was expressed to a greater extent in kidney and lung. At the light microscopic level, the silver grains observed by epipolarization or light field were seen in the specific regions or cells that express PRL receptor mRNAs. In conclusion, the long form transcript predominates in most tissues, except kidney and lung. The advantage of in situ hybridization is that it allows the identification of specific regions or cells expressing mRNAs to be identified. The actions of PRL have not been identified in all tissues expressing PRL receptor transcripts, nor has any definitive correlation been made with the expression of short and long forms of PRL receptor and function.

Adrenal Glands↗
PubMed1993

Evidence for the presence of alpha and beta-related T3 receptors in rat liver mitochondria.

Although the dependence of mitochondrial structure and function on thyroid hormone status is well established, several attempts to demonstrate a direct pathway of T3 action on mitochondria have been made during the last decade without being firmly conclusive. In this study, we present evidence firstly for the presence of specific binding sites for [125I]-T3 in rat liver mitochondria 5 min after injection, as assessed by ultrastructural autoradiography. In the same way, using immunocytological techniques and protein immunoblotting, T3 receptor-like immunoreactivity was revealed mainly in the nucleus and mitochondria of hepatocytes. Whereas the colloidal gold labeling over mitochondria was found to be specific at the ultrastructural level, these results were confirmed biochemically by Western blotting experiments which revealed the presence of two protein bands in mitochondria: a stronger one of 55 kDa and a weaker one of 48 kDa. At the opposite, receptor T3 mRNAs were not detected in mitochondria by ultrastructural in situ hybridization thus confirming that the synthesis of receptor T3 occurs in the cytoplasm and that nuclear-encoded T3 receptors may belong to the bulk of cytosolic precursor polypeptides which are targeted to and imported into mitochondria. These results confirm that a direct pathway of T3 action on mitochondria occurs in situ which could now explain how the rapid activation of several mitochondrial functions can take place within minutes after thyroid hormone injection.

Animals↗
PubMed1993

[Ultrastructural in situ hybridization. A review].

After the first studies of hybridization in 1961, Jacob et al. developed an ultrastructural in situ hybridization technique in 1971. Advances in molecular biology (preparation of probes, labeling techniques...) allowed to refine this method. The radioisotope-labeled probes used initially required prolonged exposure times to achieve autoradiographic detection. Commercially available nonradioactive antigen-labeled nucleotides decreased revelation time and increased signal resolution. The three currently used methods are respectively performed on non-embedded material, pre-embedded material, and material embedded in a hydrophilic resin. Main applications include detection of viral nucleic acids, studies of ribosome maturation, detection of animal and plant mRNAs, and chromosome mapping studies.

In Situ Hybridization↗
PubMed1993

[Ultrastructural in situ hybridization on ultrathin sections of frozen tissues].

In situ hybridization on ultrathin frozen sections can be performed with either complementary DNA or synthetic oligonucleotide probes, labeled with 35S or an antigen (biotin or digoxigenin) respectively revealed by ultrastructural autoradiographic and immunocytological techniques. Using this method, GH mRNA was found in somatotrophs, mainly in the cytoplasm (endoplasmic reticulum and cytoplasmic matrix). Ultrastructural deterioration is the main drawback of this method but is more than outweighed by high sensitivity.

Autoradiography↗
PubMed1992

Immunocytological localization of endogenous calcitonin-like molecules in the crustacean Orchestia.

Immunocytological mapping of calcitonin-like molecules (human form) performed in the terrestrial crustacean Orchestia, using PAP procedure on paraffin sections and immunogold method on ultrathin cryosections, reveals two reactive organs: central nervous system and posterior caeca of the midgut. Immunoreactivity within the nervous system is mainly located throughout perikarya and nerve fibers from both dueto- and tritocerebron and ventral nervous chain. Immunolabeling in the posterior caeca is detected on both cell components of the epithelium, with significant quantitative differences between molt and intermolt periods. The role of calcitonin-like substances in these organs is then discussed: at the nervous system level, a neuro transmitter function is suggested; the direct participation of these peptides in the regulation of calcium shifts through the caecal epithelium is hypothesized.

Animals↗
PubMed1992

Evaluation of the interaction of benzene and toluene on the urinary excretion of t,t-muconic acid in rats.

The influence of simultaneous exposure to benzene and toluene on the urine excretion of t,t-muconic acid (t,t-MA) was examined in rats. t,t-MA was measured from 24-h urine of rats subjected to a single 4-h exposure to 5 or 20 ppm benzene and/or 50, 100, 200 or 1000 ppm toluene. Coexposure lowered t,t-MA excretion in a concentration-dependent manner, especially in the 20 ppm benzene group where the decrease averaged 28, 44 and 85% after exposure to 100, 200 and 1000 ppm toluene, respectively, as compared to benzene-exposed groups alone. The data confirm the sensitivity of t,t-MA as an indicator of benzene exposure and point out that measurement of t,t-MA may underestimate the exposure to benzene in the presence of toluene.

Administration, Inhalation↗
PubMed1992

Ultrastructural non-radioactive in situ hybridization of GH mRNA in rat pituitary gland: pre-embedding vs ultra-thin frozen sections vs post-embedding.

In situ hybridization at the ultrastructural level can be carried out using three different methods: on vibratome sections before embedding in epoxy resin, on ultra-thin frozen sections, or on ultra-thin sections of tissues embedded in hydrophilic resin such as Lowicryl. With the purpose of comparing the sensitivity, resolution, and ultrastructural preservation of these three methods, we examined the expression of the growth hormone (GH) gene in anterior pituitary cells by in situ hybridization at the ultrastructural level, using a synthetic oligonucleotide complementary to the codons of the mRNA from Gln 45 to Ser 54 labeled at the 3' end of biotin-21dUTP. All these methods gave similar results: mRNA was located on the lamellar endoplasmic reticulum of somatotrophs. The pre-embedding method gave the best ultrastructural preservation, with low resolution with the enzymatic detection system and an intermediate sensitivity. A probe concentration of 10 pmol/ml was sufficient to obtain a signal. With this method gold particles could not be used without pre-treatment. The frozen section method gave the best sensitivity (a signal was observed with 4 pmol/ml of probe) but the lowest ultrastructural preservation. On ultra-thin Lowicryl sections, resolution was as high as with the frozen-section method, ultrastructural conservation was intermediate, and sensitivity was low. These results indicate that the last method seems to be a good compromise between sensitivity and ultrastructural preservation.

Animals↗