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Biomedical subjects

V K Han

Publications and source records attributed to V K Han.

At least 55 records · Page 3Linked to original sources
PubMed1995

Identification and tissue distribution of a novel variant of 11 beta-hydroxysteroid dehydrogenase 1 transcript.

A novel variant of 11 beta-hydroxysteroid dehydrogenase 1 (11 beta-HSD1) mRNA was identified from the ovine liver by reverse transcription-polymerase chain reaction (RT/PCR), and was named 11 beta-HSD1C mRNA. Sequence analysis of the RT-PCR product revealed that 11 beta-HSD1C mRNA was the product of an alternative exon-splicing within the 11 beta-HSD1 gene in which exon 5 was spliced out. Although it caused a deletion of 48 amino acids in the deduced 11 beta-HSD1 protein, this alternative splicing did not result in a shift within the predicted open reading frame of 11 beta-HSD1 cDNA. Thus, 11 beta-HSD1C mRNA was predicted to code for a protein of 244 amino acids. Using RT-PCR, we also examined the expression of 11 beta-HSD1C mRNA in ovine fetal organs and in maternal myometrium, endometrium, chorion, amnion and placenta. The 11 beta-HSD1C mRNA was expressed ubiquitously, similar to 11 beta-HSD1A mRNA, but at a lower abundance. Furthermore, since levels of 11 beta-HSD1C mRNA were directly related to those of 11 beta-HSD1A mRNA, there is no tissue-specificity for this shorter transcript and the only factor regulating its production appears to be 11 beta-HSD1A mRNA itself. To determine whether 11 beta-HSD1C mRNA encoded a functional enzyme, we inserted the cDNA into the expression vector pRc/CMV, and transfected the construct into Chinese hamster ovary cells. The transfected cells expressed a mRNA of expected size but contained no detectable 11 beta-HSD activity. When combined with cellular extracts of 11 beta-HSD1A cDNA transfected cells, they also did not alter either the dehydrogenase or reductase activity. The functional significance of the 11 beta-HSD1 transcript lacking exon 5 (11 beta-HSD1C mRNA) remains to be determined.

11-beta-Hydroxysteroid Dehydrogenases↗
PubMed1995

Insulin-like growth factor-I gene expression in the tibial epiphyseal growth plate of growth hormone-treated uremic rats.

To identify the molecular mechanisms involved in long bone growth of uremic animals, we evaluated the effects of recombinant human growth hormone (rhGH) supplementation on whole body growth, growth plate morphometrics, and insulin-like growth factor-I (IGF-I) gene expression in the tibial epiphyseal growth plates of uremic rats. Uremia was induced by a two-stage subtotal nephrectomy (Nx) of 30-day-old rats, followed by rhGH (N = 6) or saline (N = 6) treatment from day 56 to day 70 of age. Controls (N = 4) were sham decapsulated. Treatment with rhGH on Nx animals caused: (1) a significant increase in weight, (2) longitudinal growth similar to controls, and (3) increased total growth plate width predominantly due to an increase in hypertrophic zone width. rhGH increased IGF-I mRNA abundance in both zones, but the increase was greater in the proliferative zone. These changes were accompanied by concomitant alterations in IGF-I immunoreactivity. In uremic animals, therefore, rhGH treatment induces local IGF-I gene expression in the growth plate and increases the hypertrophic zone width but not the proliferative zone width. The latter suggests resistance to IGF-I action in that zone.

Animals↗
PubMed1995

Placental and fetal hepatic growth are selectively inhibited by prolonged reductions of uterine blood flow in pregnant sheep.

Experiments were conducted in eight pregnant sheep to determine the effect on fetal growth of mechanical restriction of uterine blood flow (RUBF) between 120 days and 134 days gestation. Uterine blood flow measured in the middle uterine arteries was 40% less in RUBF animals compared with control animals at the end of the experimental period. There was no change in fetal blood gases, bodyweights, or organ weights between the two groups of animals. The rate of DNA synthesis in the right lobe of the liver was significantly less in RUBF animals (581 +/- 34 dpm micrograms-1 DNA) compared with control animals (845 +/- 44 dpm microgram-1 DNA). There was no difference in the rate of DNA synthesis in the left lobe of the liver or in any of the other organs examined. Autoradiographic examination of the placental cotyledons demonstrated that most DNA synthesis in the placenta was occurring in fetal trophoblastic cells and there was a 40% reduction in the nuclear-labelling index of placental trophoblast cells. These studies show that mild mechanical reductions in uterine blood flow in pregnant sheep results in the selective inhibition of growth in the right lobe of the fetal liver and the placental trophoblastic cells. The mechanism underlying this close association remains to be determined.

Animals↗
PubMed1995

Effect of prolonged catecholamine infusion on heart rate, blood pressure, breathing, and growth in fetal sheep.

Norepinephrine and epinephrine were infused into fetal sheep for 24 h to compare the effects on fetal heart rate, blood pressure, breathing movements, and tissue growth with those of prolonged reductions in uterine blood flow. Norepinephrine concentrations increased (p < 0.01) from 871 +/- 71 to 6831 +/- 1090 pg/mL (2 h) with norepinephrine infusion, and epinephrine concentrations increased from 310 +/- 95 to 1424 +/- 288 pg/mL (2 h) with epinephrine infusion. Fetal pH decreased (p < 0.01) from 7.37 +/- 0.01 to 7.29 +/- 0.02 at 0.5 h of the norepinephrine infusion and returned to control values by 2 h, whereas fetal lactate concentrations increased (p < 0.05) from 1.6 +/- 0.2 to 4.6 +/- 1.0 mmol/L at 2 h and remained elevated for 12 h. Lactate concentrations also increased with epinephrine infusion. Fetal heart rate increased (p < 0.05) from 176 +/- 5 to 246 +/- 6 and 220 +/- 6 beats/min in the 1st h of norepinephrine and epinephrine infusions, respectively, with a subsequent decline. Fetal blood pressure increased (p < 0.05) from 43 +/- 3 and 40 +/- 2 to 53 +/- 3 and 47 +/- 2 mmHg (1 mmHg = 133.3 Pa) during the 1st h of norepinephrine and epinephrine infusions, respectively, remaining elevated for 24 h. Fetal body weights were not different between the groups of animals, although liver/body weight ratio was less (p < 0.05) in epinephrine-infused fetuses (0.030 +/- 0.001) compared with vehicle-infused animals (0.036 +/- 0.002). There was no change in DNA synthesis rate in any of the fetal organs, despite changes in organ-specific DNA and protein content. Our results indicate that the changes in fetal cardiovascular and behavioural function, as well as tissue growth, that occur with prolonged reductions in uterine blood flow are not mediated solely by elevated circulating catecholamine concentrations.

Adrenal Glands↗
PubMed1995

Expression, distribution, regulation and function of IGFs in the ovine fetal pituitary.

Activation of the fetal pituitary-adrenal axis is crucial for fetal organ maturation and the onset of parturition in sheep. Many factors including corticotrophin-releasing hormone (CRH) and arginine vasopressin secreted from the hypothalamus, and growth factors produced within the pituitary may be involved in the regulation of maturation of the fetal pituitary gland. IGFs have mitogenic and differentiation-promoting capacities in a variety of organs and are synthesized as paracrine factors within developing tissues. However, there is little information concerning the synthesis, distribution, regulation and function of IGFs in the fetal pituitary gland at different times during pregnancy. Therefore, we have localized IGF-I and IGF-II mRNAs and peptides, and determined the effect of cortisol on the level of IGF-II mRNAs in the pituitary glands of developing sheep fetuses. We examined the possible effects of IGFs on corticotroph function in cultures of adenohypophysial cells from term fetuses. Seven species of IGF-II transcripts of 1.2-6.0 kb were identified by Northern blot analysis in the pituitary gland of fetuses between day 60 of gestation and term (day 145). The levels of IGF-II mRNAs did not change significantly during pregnancy, although there was a trend for the presence of higher levels of IGF-II mRNAs at day 60 of gestation. IGF-I mRNA was not detectable. By in situ hybridization, IGF-II mRNA was localized to non-endocrine cells and to cells lining the blood vessels of the pars distalis, to some presumed endocrine cells in the pars distalis and pars intermedia, and to clusters of cells in the pars nervosa. In contrast, IGF-I and IGF-II peptides were detected in the presumed endocrine cells in the pars distalis and pars intermedia but not in the pars nervosa. Incubation of adenohypophysial cells from term fetuses with IGF-I, but not IGF-II, for 48 h increased specific 125I-Tyr-ovine CRH binding. However, neither IGF-I nor IGF-II had any significant effects on the basal or CRH-stimulated immunoreactive (ir)-ACTH output, the level of POMC mRNA or the number of ir-ACTH positive cells. Infusion of cortisol to fetuses starting at day 96 of gestation for 100 h or at days 120-125 of gestation for 84 h did not affect the level of IGF-II mRNAs in the pars distalis but decreased the levels of POMC mRNA. These results are consistent with IGFs having the potential to influence fetal pituitary function, although probably on cell types other than the corticotrophs.(ABSTRACT TRUNCATED AT 400 WORDS)

Adrenocorticotropic Hormone↗
PubMed1994

Brain growth retardation due to the expression of human insulin like growth factor binding protein-1 in transgenic mice: an in vivo model for the analysis of igf function in the brain.

Three lines of transgenic (Tg) mice carrying a fusion gene linking the mouse metallothionein-I promoter to a cDNA encoding human insulin-like growth factor binding protein-1 (hIGFBP-1) were found to express the transgene in brain. As judged by comparing Tg brain weights to those of non-transgenic littermates, adult hemizygotic Tg mice of each line exhibited brain growth retardation (16.2%, 14.4% and 8.1% reductions in weight, respectively in each line). In two lines, total brain DNA and protein content were decreased. Further analysis indicated that the brain growth retardation was manifested in the second week of postnatal life. Given that the insulin-like growth factors (IGFs) stimulate cell proliferation and/or survival in neural cultures and that hIGFBP-1, when present in a molar excess, inhibits IGF interactions with their cell surface receptors, the brain growth retardation in hIGFBP-1 Tg mice likely results from hIGFBP-1 inhibition of IGF-stimulated growth-promoting actions. These hIGFBP-1 Tg mice should prove useful in defining IGF actions during postnatal brain maturation.

Aging↗
PubMed1994

Expression of insulin-like growth factor and binding protein genes during nephrogenesis.

To study the role of insulin-like growth factors (IGFs) and their binding proteins (IGFBPs) in human nephrogenesis, we examined the temporal and spatial pattern of expression of these genes using in situ hybridization. The uninduced metanephric blastema (MB) expressed abundant IGF-II mRNA. With induction by the ureteric duct (UD), the aggregated MB additionally expressed IGFBP-2 and IGFBP-4 mRNAs. The mature UD expressed IGFBP-3 mRNA while the ampulla in contact with the MB lacked IGFBP-3 mRNA and expressed IGFBP-2 exclusively. Upon formation of the S-shape nephron, IGFBP-2 mRNA was expressed in the committed glomerular and epithelial cells which also expressed IGF-II and IGFBP-4, and the mesenchyme of the vascular cleft expressed IGFBP-5 mRNA. In the maturing glomerulus, the glomerular epithelial cells expressed IGF-II mRNA together with IGFBP-2 and IGFBP-4 mRNAs, while IGFBP-5 mRNA was localized to the mesangium and supporting mesenchyme. As the proximal tubule was formed the epithelium expressed less of IGFBP-2 mRNA and more of IGFBP-4 mRNA. The renal mesenchyme in the cortex and medulla expressed abundant IGF-II mRNA, and lower levels of IGFBP-4 and -5 mRNAs. The epithelium of the collecting ducts and pelvicalyceal system expressed abundant IGFBP-3. In contrast, IGF-I, IGFBP-1, and IGFBP-6 mRNAs were expressed at low levels. The specific temporal and spatial pattern of expression of IGFBP genes on the background of abundant IGF-II gene expression suggests that the IGFBP peptides, as modulators of IGF action, are expressed locally at specific points of nephrogenesis to interact with IGF-II to regulate mesenchymal induction, renal epithelial cell commitment, differentiation and growth.

Carrier Proteins↗
PubMed1994

Spatial and temporal distribution of insulin-like growth factors I and II during development of rat lung.

Insulin-like growth factors (IGF) I and II genes are expressed in developing lung tissue, but the details of distribution during different stages of lung development have not been delineated. To define the role of IGFs in lung development, the expression of IGF-I and IGF-II mRNAs and peptides was examined in rat lungs from 16-day gestation through adulthood. The expression of stable IGF mRNAs was investigated by Northern analysis, IGF mRNAs were localized by in situ hybridization histochemistry, and IGF peptides were localized by immunohistochemistry. Four IGF-II transcripts (3.5, 2.2, 1.8, and 1.0 kb) were identified; IGF-II mRNA levels were highest early in fetal life (day 16-18) and decreased gradually until 28 days postnatal. Four IGF-I transcripts (7.8, 4.4, 2.1, and 0.6 kb) were detected but were of low abundance. IGF-II mRNA was localized mainly in mesenchymal cells but was also identified in the airway epithelium, with peak expression in the perinatal lung. IGF-II peptide was prominent in late fetal life and for 5 days after birth and was identified in both mesenchymal and epithelial cells. In contrast, there was little evidence of IGF-I mRNA and peptide until after birth: IGF-I was most easily identified between 5 and 14 days postnatal (the height of alveolar multiplication and formation), when both mRNA and peptide were localized to mesenchymal and epithelial cells. Our studies demonstrate that IGF-I and IGF-II are synthesized and distributed in spatially and temporally different patterns in the developing lung. IGF-I and IGF-II peptides are more widely identified than their respective mRNAs, suggesting a paracrine distribution in the developing lung.

Aging↗
PubMed1994

Catecholamines stimulate the synthesis and release of insulin-like growth factor binding protein-1 (IGFBP-1) by fetal sheep liver in vivo.

In fetal sheep, prolonged hypoxia (for 24 h) induced by a reduction in maternal uterine artery blood flow, increases insulin-like growth factor binding protein-1 (IGFBP-1) levels and decreases IGFBP-2 levels in the plasma, with corresponding changes in messenger RNA (mRNA) levels in the liver. Since IGFBP-1 synthesis in liver cells in vitro is stimulated by compounds that increase intracellular cAMP concentrations, we hypothesized that the increased IGFBP-1 synthesis during prolonged hypoxemia may be induced by circulating catecholamines, that are released during hypoxia, and that elevate fetal liver cAMP levels. Our aim was to determine the effect of 24-h catecholamine infusions on the synthesis and release of IGFBP-1 and IGFBP-2 in fetal sheep. Vascular catheters were implanted into fetuses at 110-115 days gestation in 14 pregnant ewes. After a 5-day recovery period, fetuses received a 24-h infusion of either norepinephrine (1 micrograms/kg.min, n = 5), epinephrine (0.25 micrograms/kg.min, n = 5), or vehicle (normal saline, n = 4). Fetal carotid arterial samples were collected at specified intervals throughout the infusion for the determination of blood glucose concentrations, plasma catecholamine concentrations by HPLC, insulin, and glucagon concentrations by RIA, and IGFBP levels by Western ligand blotting. After 24 h, the ewe and fetus were killed and selected fetal tissues (liver and kidney) were collected, and analyzed for IGFBP mRNA levels by northern blotting followed by laser densitometric quantification. Plasma catecholamine concentrations were increased in treated fetuses to levels that may be expected in fetuses subjected to prolonged hypoxia. In epinephrine and norepinephrine infused fetuses, blood glucose and plasma glucagon concentrations were increased significantly, whereas plasma insulin concentrations were decreased significantly. Norepinephrine and epinephrine infusions increased IGFBP-1 levels significantly (2- to 5-fold) in fetal plasma within 8-12 h, and the time course pattern of elevation of plasma IGFBP-1 levels was similar to that observed in prolonged hypoxia. After 24 h of either norepinephrine or epinephrine infusion, IGFBP-1 mRNA levels in the liver of fetuses were increased significantly (5- to 7-fold) compared to those of vehicle infused fetuses. IGFBP-2, -3, and -4 levels in fetal plasma were not affected by either infusion, nor were IGFBP-2 mRNA levels in fetal liver and kidney.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1994

Hormonal regulation and biological actions of insulin-like growth factor binding proteins in isolated ovine thyroid follicles.

The ability of TSH to stimulate synthesis and release of thyroid hormones in ovine thyroid follicles in vitro depends partially on a synergy with insulin-like growth factors (IGFs). The cellular availability of IGFs may be influenced by the release of several IGF binding proteins (IGFBPs). The purposes of these studies was to 1) further characterize the species of IGFBPs synthesized by thyroid follicles, 2) examine the ability of TSH and cortisol to alter IGFBP gene expression and protein release, and 3) investigate the actions of exogenous IGFBPs on thyroid cell function. Adult sheep thyroid follicles were isolated after collagenase digestion, grown to confluence in Coon's modified Ham's F12M medium (OH) with the addition of transferrin, glycylhistidyl-lysine, somatostatin (3H), cortisol and insulin, and maintained in serum-free test media with or without further supplements for up to 48 h. Conditioned media were analyzed for IGFBP presence by Western ligand blotting, and by immunoblotting using specific antisera against bovine IGFBP-2 and human IGFBP-5. IGFBP mRNAs from follicles were identified by Northern blot hybridization using [32P]labeled complementary DNAs encoding ovine IGFBP-1 or -2, and rat IGFBP-4, -5, or -6. Uptake and organification of Na[125I] were measured by incorporation into trichloroacetic acid-precipitable material. Isolated thyroid follicles synthesized four species of IGFBPs in either 0H or 3H medium as detected by ligand blotting, of sizes 40-46, 34, 28, and 18 kilodaltons (kDa), respectively. The 32 kDa IGFBP was identified immunologically as IGFBP-2, whereas the 28 kDa and 18 kDa species were identified as IGFBP-5. Northern blot hybridization of total RNA from cells in 3H medium demonstrated an IGFBP-2 messenger RNA (mRNA) [1.4 kilobase (kb)], an IGFBP-4 mRNA (2.6 kb), and two IGFBP-5 mRNAs (6 kb and 1.8 kb). No IGFBP-1 or -6 mRNAs were detected. Incubation of cultured follicles with TSH (30-500 microU/ml) caused a dose-dependent decrease in the abundance of all IGFBP mRNAs and released proteins, which were reduced further by TSH together with cortisol (10 nM). When the inhibitory effect of TSH and cortisol was removed, IGFBP-2 mRNA increased within 3 h and was 7-fold greater within 12 h. IGFBP-2 did not appear in the conditioned medium until 12 h after TSH removal, along with the other IGFBP species.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1994

Regulation of insulin-like growth factor-II gene expression in the ovine fetal adrenal gland by adrenocorticotropic hormone and cortisol.

Maturation and activation of the fetal adrenal gland is crucial to fetal organ maturation and the onset of parturition in sheep. Insulin-like growth factors (IGFs) have been demonstrated to promote fetal adrenal mitogenesis and steroidogenesis in some species. Our previous studies showed that IGF-II mRNA is expressed in the steroidogenic cells of the fetal sheep adrenal, suggesting that IGF-II may be an important regulator of fetal adrenal function. However, the regulation of IGF-II gene expression is poorly understood. In the present study we measured the changes in IGF-II mRNA level in fetal sheep adrenals during late gestation in response to ACTH and cortisol. Either saline (0.5 ml/h) or cortisol (1 mg/24 h) was infused for 100 h to fetal sheep beginning on day 95 or 96 of pregnancy, or saline (0.5 ml/h), ACTH (0.5 micrograms/h) or cortisol (1 mg/h) was infused for 84 h to fetal sheep beginning on days 120-125 of pregnancy (term = 145 days). Adrenal RNA was subjected to Northern blot analysis with an ovine IGF-II cDNA probe. The relative abundance of total IGF-II mRNA decreased significantly in the ACTH- and cortisol-treated fetuses. IGF-II mRNA was localized by in situ hybridization using a 35S-labeled antisense ovine IGF-II cRNA probe, and IGF-II peptide was localized by immunohistochemistry. There were no differences in the cellular distribution patterns of IGF-II mRNA and IGF-II peptide after treatments, but the intensity of the hybridization signal for IGF-II mRNA and of immunostaining for IGF-II peptide decreased in adrenals from fetuses treated with ACTH or cortisol. These results suggest that ACTH and cortisol decrease IGF-II gene expression in the ovine fetal adrenal. We speculate that the cortisol surge observed in the late gestation ovine fetus may be responsible for down-regulation of IGF-II gene expression in the fetal adrenal at or just before birth.

Adrenal Glands↗
PubMed1994

The ontogeny of insulin-like growth factor (IGF) and IGF-binding protein gene expression in the rat pancreas.

Insulin is important for optimal fetal and neonatal growth and development. Its continued availability is due, in part, to ongoing islet cell growth within the pancreas. IGFs and IGF-binding proteins (IGFBPs) have been implicated as paracrine regulators of islet cell growth within the developing pancreas. The purpose of this study was to determine whether the intact rat pancreas expresses mRNAs for IGF-I, IGF-II and IGFBPs, and how these might change with development. Liver was studied as a control tissue. Pancreas and liver were taken from fetal rats at 20-22 days of gestation, from postnatal rats at 1-21 days and from adult animals, and mRNAs for IGFs-I and -II and IGFBPs-1 to -6 were detected by Northern blot hybridization. The amount of IGF-II mRNA was greatest in the liver and pancreas of the fetal rat, and declined in both tissues during the neonatal period. Conversely, IGF-I mRNA levels were low but detectable in fetal life, and rose to adult levels within 2 weeks of birth. Both IGFBP-1 and IGFBP-2 mRNAs were present in fetal rat liver, increasing in amount over the first week of life, and declining in the adult. However, within the pancreas, IGFBP-1 mRNA was undetectable and IGFBP-2 mRNA was very low in the fetus and neonate. Both IGFBP-1 and IGFBP-2 mRNAs transiently appeared in the pancreas between postnatal weeks 2 and 3 and declined in the adult. IGFBP-3 and IGFBP-4 mRNAs were detected in both the liver and pancreas throughout the developmental period studied. IGFBP-3 mRNA increased in amount immediately following birth, while the quantity of IGFBP-4 mRNA increased sharply in liver from postnatal day 21, but declined in the pancreas. mRNA for IGFBP-5 or -6 was undetectable in either tissue. The reslts show that both IGF-I and IGF-II are expressed by rat pancreas from at least 20 days of gestation, the latter being predominant in fetal life and the former during postnatal development. In addition, at least four IGFBP mRNAs (IGFBPs-1, -2, -3 and -4) were expressed within the pancreas with distinct developmental patterns. IGFBP-3 and -4 were predominant in the fetal and neonatal periods, while increased expression of IGFBPs-1 and -2 occurred 2-3 weeks after birth. The ontogeny of IGFBP mRNA expression in pancreas differed from that in liver.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1993

Alterations in the synthesis of insulin-like growth factor binding proteins and insulin-like growth factors in rat C6 glioma cells transfected with a gap junction connexin43 cDNA.

When C6 glioma cells are stably transfected with a connexin43 cDNA and gap junctions are increased, the rate of cellular proliferation is decreased. To determine if this phenomenon is related to alterations in IGFBP and IGF synthesis, we have compared IGFBPs and IGFs in the conditioned media from primary rat astroglia, C6, and transfected C6 clones Cx43-13 (high expresser), and Cx43-12 and Cx43-14 (intermediate expressers). Primary astroglia produced IGFBP-2 (34 kDa) and IGFBP-3 (40-45 kDa). C6 cells synthesized high levels of IGFBP-3 and low levels of IGFBP-2, and a 24 kDa IGFBP (IGFBP-4). Cx43-13 cells did not synthesize IGFBP-3, but produced low levels of IGFBP-2 and high levels of IGFBP-4. Cx43-12 and Cx43-14 secreted IGFBP profiles similar to the parent C6 line, but with reduced levels of IGFBP-2. The lack of IGFBP-3 in Cx43-13 cells was not due to the presence of proteases. Northern analysis showed IGFBP-2 mRNA to be readily detectable only in the primary astroglia. IGFBP-3 mRNA was detected in the primary astroglia, C6, Cx43-12 and Cx43-14, but not in Cx43-13. In contrast, IGFBP-4 mRNA was readily detected only in the Cx43-13. IGF-II concentrations in the media were low to undetectable for both C6 and transfected cells. IGF-I concentrations were significantly lower in the media from transfected cells compared to the C6 cells. Stable mRNA levels for IGF-I were lower in transfected cells, with the lowest levels observed in the Cx43-13 cells. Although C6 cells did not respond mitogenically to exogenous IGF-I or IGF-II, Cx43-13 cells responded to IGF-I or IGF-II in a dose dependent manner. Conditioned media from Cx43-13 cells decreased the DNA synthesis of C6 cells, and this effect could be reversed by the addition of IGF-II. The decreased synthesis of the autocrine/paracrine growth factor IGF-I together with decreased levels of a positive modulator IGFBP-3, and the increased levels of a negative modulator IGFBP-4 in the extracellular milieu, may be responsible for the reduced proliferative capacity in cells expressing abundant connexin43.

Animals↗
PubMed1993

Transcription termination/polyadenylation occurs at multiple sites in the human type I interferon receptor gene.

Based on the previously reported sequence, we isolated an independent cDNA clone encoding a binding component of the human type I interferon receptor (IFN-R). This cDNA is identical to the published sequence except that it lacks 62 bases of 5' untranslated sequence and terminates at the first of two potential polyadenylation sites. In Northern blot analyses of poly(A)+RNAs from both IFN-sensitive and IFN-resistant Daudi cells, this cloned cDNA hybridized to a predominant mRNA of 2.4 kb, as well as to mRNAs of 1.8, 4.8, and 5.6 kb, and occasionally 6.9 kb. These various transcripts, which were also observed at similar levels in Raji B cells and two T-cell lines, Jurkat and MOLT-4, were detected after high-stringency washes, and by alternate probes corresponding to subfragments of the cDNA. In contrast, only the 4.8- and 5.6-kb transcripts hybridized to a polymerase chain reaction (PCR)-derived probe that corresponded to genomic sequences immediately down-stream from the second polyadenylation site. These results indicate that the latter transcripts arise from the same gene as the predominant 2.4-kb mRNA due to incomplete transcription termination at either of the known polyadenylation sites. Finally, Northern blot analysis of total RNAs revealed the presence of the predominant 2.4-kb type I IFN-R transcript in numerous tissues from second trimester human fetuses, suggesting that the type I IFN-R gene is constitutively expressed in multiple cell types.

Cell Line↗
PubMed1993

Localization of transforming growth factor alpha in the human placenta and decidua: role in trophoblast growth.

Transforming growth factor alpha (TGF alpha) is an important growth regulatory molecule, the location and function of which at the human fetomaternal interface remain to be determined. The present study examined the presence of TGF alpha in the human placenta, decidua, and fetal membranes throughout gestation (from a total of 29 subjects) as well as its functional role in the proliferation of first trimester trophoblasts. The peptide was localized immunocytochemically with a monoclonal anti-TGF alpha antibody (Ab) (MF9) on paraffin-embedded tissues via the avidin-biotin complex-peroxidase technique with diaminobenzidine (DAB) as the chromogen. Omission or TGF alpha absorption of the primary Ab served as negative controls. Specific (cytoplasmic) staining was noted in typical stromal-type decidual cells, including cells of the decidua basalis and parietalis and chorionic decidua, throughout gestation. Villous trophoblast cells (syncytiotrophoblast and to a minor extent cytotrophoblast) at all gestational ages as well as extravillous cytotrophoblast cells (intermediate and cytotrophoblastic shell) also showed specific cytoplasmic staining. Chorionic trophoblasts showed variable staining, and little or no immunoreactivity was seen in the amniocytes. Second-passage first trimester human trophoblast cells (characterized by their expression of cytokeratin as well as other markers) were cultured in the presence of TGF alpha or neutralizing anti-TGF alpha Ab (TAb-1) or no additive for 18 h prior to exposure to 3H-TdR for 6 h to measure 3H-TdR uptake. TGF alpha (0-100 ng/ml) caused a dose-dependent stimulation of proliferation, reaching a near plateau at 6-100 ng/ml to slightly more than double the basal level. The presence of anti-TGF alpha Ab alone (25 micrograms/ml) did not significantly influence the proliferation of the cells, indicating the absence of significant endogenous TGF alpha in these cultures; however, the Ab was able to abolish the stimulatory function of exogenous TGF alpha. Exogenous TGF alpha also increased the number of trophoblast nuclei immunoreactive for proliferating cell nuclear antigen and reduced the incidence of multinucleate cells in culture. These results indicate that TGF alpha is present in the cells of the fetomaternal interface throughout human gestation and may function as a stimulator of trophoblastic growth in situ.

Cell Division↗
PubMed1993

Pathophysiology, cellular and molecular mechanisms of foetal growth retardation.

In mammals, size at birth is the outcome of length of gestation and rate of foetal growth. In the absence of premature delivery, foetal size within species is determined principally by foetal growth rate which is dependent on both genetic and epigenetic factors. Failure of either of these mechanisms leads to foetal growth retardation. In mammals, including human infants, foetal growth retardation can occur naturally or pathologically. One major cause for natural foetal growth retardation or runting is the increase in litter size. In many cases, however, the cause of runting is unknown. Parental genotype or antigenic differences between the mother and the developing conceptus may be potential causes. Pathological foetal growth retardation or intrauterine growth retardation (IUGR) is due to genetic causes (chromosomal abnormalities or inherited syndromes) or epigenetic causes (intrauterine infections, toxins and chemicals, maternal diseases of pregnancy affecting the placenta). The underlying pathophysiological processes that occur at the cellular and molecular level in IUGR are still unknown. Reduction in the supply of substrates that are necessary for normal cellular function, and alteration in mediator molecules that regulate cellular growth and differentiation, are important mechanisms. A decrease in growth promoting factors or an increase in growth inhibitory factors may lead to growth failure. Growth factors and their receptors are expressed in the developing embryo (as early as the 1-2-cell stage), placenta and maternal uterine tissues, suggesting that these molecules may play a role in regulating normal growth and differentiation of the conceptus as well as maternal reproductive tissues. The local expression within developing tissues indicates that these factors act in either autocrine or paracrine mechanism. Recent studies using gene targeting to knock out one allele of insulin-like growth factor II (IGF II) gene in mice which resulted in growth retarded pups at birth, strongly support the importance of local IGF II in regulating tissue growth. Foetal growth retardation has also been induced experimentally in several species using one of the following methods: (i) maternal undernutrition, (ii) chronic hypoxia, (iii) prolonged reduction in uterine blood flow, (iv) reduction in placental size, and (v) endocrine alterations. These models provide useful information on the physiological mechanisms underlying a specific type of growth retardation. These in-vivo models and in-vivo tissue culture models can now be analysed by biochemical and molecular biological techniques to unravel the basic mechanisms that underlie foetal growth retardation.

Animals↗