Sequences of liver cDNAs encoding two different mouse insulin-like growth factor I precursors

Elevated levels of the chemokine GRO-1 correlate with elevated oligodendrocyte progenitor proliferation in the jimpy mutant

The dysmyelinating mutant jimpy (jp) arises from a point mutation in the mouse gene encoding proteolipid protein and is characterized by severe dysmyelination attributable to oligodendrocyte death. This mutant was used to investigate the regulation of oligodendrocyte progenitor proliferation in the postnatal spinal cord. At postnatal day 18, jp spinal cord contained a three- to eightfold greater number of proliferating oligodendrocyte progenitor cells than did wild-type (wt) spinal cord. Increased proliferation in jp spinal cord was accompanied by a twofold increase in the number of progenitor cells. Semiquantitative reverse transcriptase-PCR revealed no change in the level of mRNA encoding the platelet-derived growth factor A, transforming growth factor-beta, or insulin-like growth factor-I, all of which have been implicated as regulators of proliferation and differentiation of oligodendrocyte progenitor cells. There was, however, a 17-fold increase in the level of mRNA encoding the chemokine GRO-1 and a 5- to 6-fold increase in GRO-1 protein in the jp spinal cord. Double immunofluorescence labeling revealed elevated levels of GRO-1 in reactive astrocytes in jp spinal cord white matter. In vitro studies indicated that extracts from jp spinal cord stimulated oligodendrocyte progenitor proliferation. Furthermore, removal of GRO-1 from jp extracts by immunoprecipitation reduced the proliferation of progenitor cells to a level similar to that achieved by wt extracts. These findings suggest a novel mechanism by which proliferation of oligodendrocyte progenitor cells is regulated in the postnatal spinal cord in response to insult.

Elevated levels of the chemokine GRO-1 correlate with elevated oligodendrocyte progenitor proliferation in the jimpy mutant

The dysmyelinating mutant jimpy (jp) arises from a point mutation in the mouse gene encoding proteolipid protein and is characterized by severe dysmyelination attributable to oligodendrocyte death. This mutant was used to investigate the regulation of oligodendrocyte progenitor proliferation in the postnatal spinal cord. At postnatal day 18, jp spinal cord contained a three- to eightfold greater number of proliferating oligodendrocyte progenitor cells than did wild-type (wt) spinal cord. Increased proliferation in jp spinal cord was accompanied by a twofold increase in the number of progenitor cells. Semiquantitative reverse transcriptase-PCR revealed no change in the level of mRNA encoding the platelet-derived growth factor A, transforming growth factor-beta, or insulin-like growth factor-I, all of which have been implicated as regulators of proliferation and differentiation of oligodendrocyte progenitor cells. There was, however, a 17-fold increase in the level of mRNA encoding the chemokine GRO-1 and a 5- to 6-fold increase in GRO-1 protein in the jp spinal cord. Double immunofluorescence labeling revealed elevated levels of GRO-1 in reactive astrocytes in jp spinal cord white matter. In vitro studies indicated that extracts from jp spinal cord stimulated oligodendrocyte progenitor proliferation. Furthermore, removal of GRO-1 from jp extracts by immunoprecipitation reduced the proliferation of progenitor cells to a level similar to that achieved by wt extracts. These findings suggest a novel mechanism by which proliferation of oligodendrocyte progenitor cells is regulated in the postnatal spinal cord in response to insult.

The megencephaly mouse has disturbances in the insulin-like growth factor (IGF) system

Megencephaly, enlarged brain, is a major sign in several human neurological diseases. The mouse model for megencephaly, mceph/mceph, has an enlarged brain and a lowered body weight. In addition, it displays several neurological and motoric disturbances. Previous studies suggest that the brain enlargement results from hypertrophy of the brain cells, rather than hyperplasia. No structural abnormalities, edema or increased myelination have been found. In this study, a major imbalance in the mRNA expression of molecules in the insulin-like growth factor (IGF) system was found in brains of 9-10 weeks old mceph/mceph mice compared to +/+ wild-type mice. In mceph/mceph brains, we found upregulation of IGF binding proteins (BP)-2, -4, -5, and -6 mRNA, the regulating hormone transforming growth factor (TGF)beta1 mRNA and also a local downregulation of IGFBP-5 mRNA compared to wild-type brains by in situ hybridization. The altered expression of these mRNA species is colocalized in cerebral cortex, hippocampus, amygdala and piriform/entorhinal cortex. The mceph/mceph mice express less of the myelin component proteolipid protein (PLP) mRNA in corpus callosum. No expression difference of the housekeeping gene glyceraldehyde-3-phosphate dehydrogenase (GAPDH) in brain or IGF system components in liver was found between mceph/mceph and wild-type mice. These data suggest that the IGF system has an important role in the excessive growth of the mceph/mceph brains.

Developing Schwann cells acquire the ability to survive without axons by establishing an autocrine circuit involving insulin-like growth factor, neurotrophin-3, and platelet-derived growth factor-BB

Although Schwann cell precursors from early embryonic nerves die in the absence of axonal signals, Schwann cells in older nerves can survive in the absence of axons in the distal stump of transected nerves. This is crucially important, because successful axonal regrowth in a damaged nerve depends on interactions with living Schwann cells in the denervated distal stump. Here we show that Schwann cells acquire the ability to survive without axons by establishing an autocrine survival loop. This mechanism is absent in precursors. We show that insulin-like growth factor, neurotrophin-3, and platelet-derived growth factor-BB are important components of this autocrine survival signal. The secretion of these factors by Schwann cells has significant implications for cellular communication in developing nerves, in view of their known ability to regulate survival and differentiation of other cells including neurons.

Developing Schwann cells acquire the ability to survive without axons by establishing an autocrine circuit involving insulin-like growth factor, neurotrophin-3, and platelet-derived growth factor-BB

Although Schwann cell precursors from early embryonic nerves die in the absence of axonal signals, Schwann cells in older nerves can survive in the absence of axons in the distal stump of transected nerves. This is crucially important, because successful axonal regrowth in a damaged nerve depends on interactions with living Schwann cells in the denervated distal stump. Here we show that Schwann cells acquire the ability to survive without axons by establishing an autocrine survival loop. This mechanism is absent in precursors. We show that insulin-like growth factor, neurotrophin-3, and platelet-derived growth factor-BB are important components of this autocrine survival signal. The secretion of these factors by Schwann cells has significant implications for cellular communication in developing nerves, in view of their known ability to regulate survival and differentiation of other cells including neurons.

The renal lesions that develop in neonatal mice during angiotensin inhibition mimic obstructive nephropathy

BACKGROUND

Inhibition of angiotensin action, pharmacologically or genetically, during the neonatal period leads to renal anomalies involving hypoplastic papilla and dilated calyx. Recently, we documented that angiotensinogen (Agt -/-) or angiotensin type 1 receptor nullizygotes (Agtr1 -/-) do not develop renal pelvis nor ureteral peristaltic movement, both of which are essential for isolating the kidney from the high downstream ureteral pressure. We therefore examined whether these renal anomalies could be characterized as "obstructive" nephropathy.

METHODS

Agtr1 -/- neonatal mice were compared with wild-type neonates, the latter subjected to surgical complete unilateral ureteral ligation (UUO), by analyzing morphometrical, immunohistochemical, and molecular indices. Agtr1 -/- mice were also subjected to a complete UUO and were compared with wild-type UUO mice by quantitative analysis. To assess the function of the urinary tract, baseline pelvic and ureteral pressures were measured.

RESULTS

The structural anomalies were qualitatively indistinguishable between the Agtr1 -/- without surgical obstruction versus the wild type with complete UUO. Thus, in both kidneys, the calyx was enlarged, whereas the papilla was atrophic; tubulointerstitial cells underwent proliferation and also apoptosis. Both were also characterized by interstitial macrophage infiltration and fibrosis, and within the local lesion, transforming growth factor-beta 1, platelet-derived growth factor-A and insulin-like growth factor-1 were up-regulated, whereas epidermal growth factor was down-regulated. Moreover, quantitative differences that exist between mutant kidneys without surgical obstruction and wild-type kidneys with surgical UUO were abolished when both underwent the same complete surgical UUO. The hydraulic baseline pressure was always lower in the pelvis than that in the ureter in the wild type, whereas this pressure gradient was reversed in the mutant.

CONCLUSION

The abnormal kidney structure that develops in neonates during angiotensin inhibition is attributed largely to "functional obstruction" of the urinary tract caused by the defective development of peristaltic machinery.

Expression of insulin-like growth factor binding protein-4, insulin-like growth factor-I receptor, and insulin-like growth factor-I in the mouse uterus throughout the estrous cycle

Recent evidence suggests that a regulated insulin-like growth factor (IGF) system mediates the effects of estrogen, promoting the proliferation and differentiation of specific uterine cell types throughout the estrous cycle and during gestation in the rodent. Previous studies have shown that IGFs are differentially expressed in the mouse uterus during the periimplantation period. In the current study, we examined the expression of IGF binding protein-4 (IGFBP-4), IGF-I receptor (IGF-IR), and IGF-I in the mouse uterus throughout the estrous cycle. Ligand blot analysis was conducted on uterine homogenates using [125I]IGF-I. IGFBP-4 was detected in all uterine homogenates, varying in intensity throughout the estrous cycle. In situ hybridization studies at metestrus and diestrus demonstrated an intense IGFBP-4 mRNA signal in antimesometrial stromal cells between the luminal epithelium and the myometrium, but at proestrus and estrus, no IGFBP-4 signal was detected. No IGF-I mRNA was detected at any stage of the estrous cycle by in situ hybridization. However, by RT-PCR analysis, IGF-I mRNA was detected at all stages of the estrous cycle. RT-PCR analysis also showed IGF-IR mRNA throughout the estrous cycle. Using immunohistochemistry, IGF-IR immunostaining was detected throughout the estrous cycle and on days 2-7 of gestation, but was restricted to the glandular epithelium. These results suggest that uterine IGFBP-4 expression may not be dependent on uterine IGF-I expression. They also suggest that IGFBP-4 may play a role in uterine physiology independent of the inhibition of IGF-I action, and that IGF-IR is constitutively expressed in the mouse uterus.

A role for the POU-III transcription factor Brn-4 in the regulation of striatal neuron precursor differentiation

Both insulin-like growth factor-I (IGF-I) and brain-derived neurotrophic factor (BDNF) induce the differentiation of post-mitotic neuronal precursors, derived from embryonic day 14 (E14) mouse striatal multipotent stem cells. Here we ask whether this differentiation is mediated by a member of the POU-III class of neural transcription factors. Exposure of stem cell progeny to either IGF-I or BDNF resulted in a rapid upregulation of Brn-4 mRNA and protein. Indirect immunocytochemistry with Brn-4 antiserum showed that the protein was expressed in newly generated neurons. Other POU-III genes, such as Brn-1 and Brn-2, did not exhibit this upregulation. Basic FGF, a mitogen for these neuronal precursors, did not stimulate Brn-4 expression. In the E14 mouse striatum, Brn-4-immunoreactive cells formed a boundary between the nestin-immunoreactive cells of the ventricular zone and the beta-tubulin-immunoreactive neurons migrating into the mantle zone. Loss of Brn-4 function during the differentiation of stem cell-derived or primary E14 striatal neuron precursors, by inclusion of antisense oligonucleotides, caused a reduction in the number of beta-tubulin-immunoreactive neurons. These findings suggest that Brn-4 mediates, at least in part, the actions of epigenetic signals that induce striatal neuron-precursor differentiation.

Gene and cDNA structures of flounder insulin-like growth factor-I (IGF-I): multiple mRNA species encode a single short mature IGF-I

To understand the comprehensive mechanisms of gene expression and processing for insulin-like growth factor-I (IGF-I) in vertebrates, we have investigated the gene organization, promoter and transcriptional initiation sites, alternative splicing and polyadenylating sites, and the cDNA structures of this gene in the Japanese flounder, Paralichthys olivaceus. The flounder IGF-I gene was found to be composed of five exons and four introns spanning 17.5 kb. By Northern blot analysis, two major mRNA classes of 4.7 kb and 2.9 kb were found in the liver. cDNA cloning and reverse transcription polymerase chain reaction (RT-PCR) analysis indicated that these two mRNA classes result from two different-sized 3'-noncoding regions generated by alternative usage of two polyadenylating signals. Further analysis by RT-PCR and sequencing revealed that these mRNA classes both contain two subclasses of mRNA encoding two forms of IGF-I prepropeptide, preproIGF-I-1 and preproIGF-I-2. The two forms of preproIGF-I share the identical signal peptide and mature IGF-I domain but contain different E domains as a result of alternative splicing in exon 3. The mature form of flounder IGF-I was found to comprise 68 amino acid residues, showing a small molecular weight, 7486. In the 5'-flanking region, one major and four minor transcription start sites have been identified by ribonuclease protection assay between -230 and -130 from the translation initiation codon, but no canonical TATA box or GC box was detected in their upstream regions up to -724. The results suggest that some unknown transcription initiation factors are functioning in the promotion of IGF-I gene expression.

Antisense fosB RNA inhibits thrombin-induced hypertrophy in cultured pulmonary arterial smooth muscle cells

BACKGROUND

We have previously reported that fosB mRNA is induced by hypertrophic stimuli (thrombin, angiotensin II) but not proliferative stimuli (platelet-derived growth factor, basic fibroblast growth factor) in pulmonary arterial smooth muscle cells (PASMCs) (J Biol Chem. 1994;9:6399-6404). Our aim in the present study was to investigate the potential role of FosB in PASMC hypertrophy.

METHODS AND RESULTS

Adenoviruses carrying sense or antisense fosB RNA expression cassettes were used to infect cultured PASMCs with the aim of increasing or inhibiting fosB expression, respectively. We examined whether fosB expression modification affected the growth of quiescent PASMCs, thrombin-induced hypertrophy, or platelet-derived growth factor-induced proliferation. PASMC growth was assessed by daily cell number count, determination of [3H]leucine incorporation, and quantification of total cellular protein. Neither an increase nor a decrease in FosB protein expression caused a significant change in the growth of quiescent PASMCs over a period of 96 hours, indicating that FosB alone is not sufficient to induce hypertrophy. Modification of FosB levels did not affect platelet-derived growth factor-induced PASMC proliferation. An increase in FosB expression did not augment thrombin-induced hypertrophy; however, inhibition of FosB expression resulted in a diminution of thrombin-induced hypertrophy by 58+/-6% (P<0.005).

CONCLUSIONS

These results suggest that FosB is necessary but not sufficient for thrombin-induced hypertrophy in cultured PASMCs.

The phylogeny of the insulin-like growth factors

The insulin-like growth factors are major regulators of growth and development in mammals and their presence in lower vertebrates suggests that they played a similarly fundamental role throughout vertebrate evolution. While originally perceived simply as mediators of growth hormone, on-going research in mammals has revealed several hierarchical layers of complexity in the regulation of ligand bioavailability and signal transduction. Our understanding of the biological role and mechanisms of action of these important growth factors in mammals patently requires further elucidation of the IGF hormone system in the simple model systems that can be found in lower vertebrates and protochordates. This review contrasts our knowledge of the IGF hormone system in mammalian and nonmammalian models through comparison of tissue and developmental distributions and gene structures of IGF system components in different taxa. We also discuss the evolutionary origins of the system components and their possible evolutionary pathways.

Cloning of a full-length insulin-like growth factor-I complementary DNA in the goldfish liver and ovary and development of a quantitative PCR method for its measurement

Five forms of insulin-like growth factor-I (IGF-I) complementary DNA (cDNA) were isolated by PCR from goldfish liver and ovary, using primers based on common carp IGF-I sequence. In the goldfish liver, we cloned and sequenced three IGF-I forms (1,2, and 3), and elucidated the full-length cDNA sequence using the 5'-and 3'-RACE. Two IGF-I forms (1 and 2) were cloned from the goldfish ovary and were found to have differences with respect to both size and nucleotide sequence compared to liver IGF-I. The entire liver IGF-I form 1 sequence was found to be 833 nucleotides long, containing a 483-nucleotide open reading from encoding 161 amino acids. The deduced amino acid sequence of the mature peptide was compared to IGF-I sequences of other vertebrates, and found to have 97 and 93% similarity to carp and salmon IGF-I, respectively, In this study we also developed a competitive quantitative PCR method and demonstrated an increase in IGF-I expression following treatments with growth hormone or gonadotropin-releasing hormone in the goldfish liver.

Alternative splicing of insulin-like growth factor I mRNA is developmentally regulated in the rat and mouse with preferential exon 2 usage in the mouse

The synthesis of an IGF-I complementary RNA (cRNA) standard containing the primer sequences for each of the four IGF-I mRNA alternative transcript forms (class 1Ea, 1Eb, 2Ea and 2Eb) and a polyA+ tail allowed the determination of the absolute abundance of each form in growing rats and mice by quantitative RT-PCR. In rat liver, class 1Ea mRNA was the most abundant form representing 90% of the total IGF-I mRNA. Though the relative proportion was maintained, the absolute abundance was maximal at 4 weeks of age and had declined by 6 weeks. In contrast, class 2Ea mRNA was the predominant transcript in mouse liver (70% of total IGF-I mRNA) and the 2Eb mRNA form was also 10-fold higher than that detected in rat liver. These results suggest that rats and mice differ both in their transcription initiation at two leader exons and in their alternative splicing activities for exon 5.

Induction of IGF-1 mRNA expression following traumatic injury to the postnatal brain

A variety of adult, non-neural tissues respond to injury by increasing expression of the gene which encodes for insulin-like growth factor-1 (IGF-1). This response is thought to be a key component in the regenerative capacity of these tissues. In contrast, the central nervous system (CNS) has relatively little regenerative capacity following injury. Interestingly, compared to many non-neuronal tissues, little IGF-1 mRNA can be detected in the adult CNS, raising the possibility that its lack of regenerative capacity is related its relative lack of IGF-1 expression. However, in the 2-week-old adolescent CNS IGF-1 mRNA can be detected in numerous brain regions. Therefore, the purpose of this study was to determine the responsiveness of the IGF-1 gene to injury in adolescent CNS tissue, a period in which expression of this gene is relatively abundant. Expression of IGF-1 mRNA was measured by means of a sensitive solution hybridization/RNase protection assay in the parieto-occipital lobes of 2-week-old and adult mice following penetrating injury. Levels of IGF-1 transcript in the injured brains were significantly increased above those of controls in both 2-week-old and adult brains 3-day post injury and remained elevated for 1 week after injury. These observations demonstrate that the adult CNS, like other tissues, can respond to injury by increasing expression of IGF-1 mRNA.

Molecular regulation of insulin-like growth factor-I and its principal binding protein, IGFBP-3

The insulin-like growth factors (IGFs) have diverse anabolic cellular functions, and structure similar to that of proinsulin. The distribution of IGFs and their receptors in a wide variety of organs and tissues enables the IGFs to exert endocrine, paracrine, and autocrine effects on cell proliferation and differentiation, caloric storage, and skeletal elongation. IGF-I exhibits particular metabolic responsiveness, and circulating IGF-I originates predominantly in the liver. Hepatic IGF-I production is controlled at the level of gene transcription, and transcripts are initiated largely in exon 1. Hepatic IGF-I gene transcription is reduced in conditions of protein malnutrition and diabetes mellitus, and our laboratory has used in vitro transcription to study mechanisms related to diabetes. We find that the presence of sequences downstream from the major transcription initiation sites in exon 1 is necessary for the diabetes-induced decrease in IGF-I transcription. Six nuclear factor binding sites have been identified within the exon 1 downstream region, and footprint sites III and V appear to be necessary for metabolic regulation; region V probes exhibit a decrease in nuclear factor binding with hepatic nuclear extracts from diabetic animals. IGFs in biological fluids are associated with IGF binding proteins, and IGFs circulate as a 150-kDa complex that consists of an IGF, an IGFBP-3, and an acid-labile subunit. Circulating IGFBP-3 originates mainly in hepatic nonparenchymal cells, where IGF-I increases IGFBP-3 mRNA stability, but insulin increases IGFBP-3 gene transcription. Regulation of IGFBP-3 gene transcription by insulin appears to be mediated by an insulin-responsive element, which recognizes insulin-responsive nuclear factors in both gel mobility shift assays and southwestern blots. Studies of mechanisms underlying the modulation of IGF-I and IGFBP-3 gene transcription, and identification of critical nuclear proteins involved, should lead to new understanding of the role and regulation of these important growth factors in diabetes mellitus and other metabolic disorders.

Isolation and characterization of tilapia (Oreochromis mossambicus) insulin-like growth factors gene and proximal promoter region

To understand the molecular mechanism which controls the transcription of the insulin-like growth factors (IGFs) gene, we have cloned and sequenced the cDNA for the proximal promoter region of the tilapia IGFs gene and have characterized its activity by chloramphenicol acetyltransferase (CAT) transient transfected expression assays. Tilapia (Oreochromis mossambicus) IGF-I cDNA (549 bp) was amplified by PCR from single-stranded cDNA of growth hormone (GH)-induced liver RNA using a pair of oligonucleotides specific for fish IGF-I as amplification primers. Tilapia IGF-I and IGF-II 5' termini were analyzed by rapid amplification of cDNA 5' ends (5'RACE). Analysis of the 5'RACE results revealed two transcription start sites in IGF-I and one transcription start site in IGF-II. Different fragments of the 5' flanking region were transfected into human lung adenocarcinoma cells. In the cell line, maximum promoter activity was located in the distal 657 basepairs of the IGF-I 5' flanking region and in the distal 450 basepairs of the IGF-II 5' flanking region. The in vivo actions of the IGFs promoter on developmental stage expression were investigated further in transgenic zebrafish in which an IGFs promoter-driven green fluorescent protein (GFP) encoding the cDNA transgene was microinjected into embryos. Morphologic and RT-PCR studies of the transgenic zebrafish indicated that IGF-I promoter-driven GFP transcripts appeared for the first time in the 1-K-cell stage and the IGF-II promoter-driven GFP transcripts appeared for the first time in the 32-cell stage. Fluorescent (GFP) distribution was apparent within 48 h in IGF-II-transgenic zebrafish embryos, especially in eye, muscle, corpuscle, floor plate, horizontal myoseptum, yolk sac extension, and yolk sac. These results indicate that the IGF-I and IGF-II promoters are active in tissue and in a development-specific manner. Our findings also indicate that the IGF-II promoter influences the growth of fish embryos earlier than does IGF-I, and IGF-II has higher levels of expression than does IGF-I. These results suggest that the IGF-II promoter plays a growth factor role in teleost embryo development.

Growth hormone gene expression and secretion in aging rats is age dependent and not age-associated weight increase related

GH secretion declines with age in rats and humans and a reduction in GH gene expression has been demonstrated in aging rats. GH secretion also diminishes in obesity; thus, the aim of this study was to determine whether GH decrease in aging rats is due to body weight gain or to aging. Three groups of male Wistar rats of different ages were studied (young, 3 months; middle-aged, 11 months; old, 27 months). The middle-aged group was established on a statistical analysis and corresponded to the youngest age at which body weight was not significantly different from the old (27 month) group. Thus, by using this group as control for comparison with animals with the same weight and an older age, the effects due to aging itself could be determined. Body weight (g, mean +/- sD) 3 months: 361 +/- 5.6; 11 months: 713 +/- 39; 27 months: 635 +/- 38. In comparison with 3-month-old rats, the 11-month-old animals showed no difference in pituitary GH messenger RNA (mRNA) accumulation and pituitary and serum IR-GH levels. Similarly IGF-I.a, IGF-I.b mRNA transcripts and IG-FBP-3 mRNA accumulation in the liver showed no significant differences between the two groups. On the contrary, when the 27-month-old rats were compared with the 11-month-old animals, lower levels of pituitary GH mRNA and serum and pituitary IR-GH were found. Pituitary GH mRNA decreased 37.5 +/- 7.7% P < 0.001, pituitary IR-GH content diminished (5.2 +/- 3.4 vs. 55 +/- 10.7 ng/mg of protein, P < 0.001) and serum IR-GH decreased (3.5 +/- 1.8 vs. 12.5 +/- 4.2 ng/ml, P < 0.01). Liver IGF-I.a and IGF-I.b mRNA transcripts accumulation and serum IGF-I were significantly diminished. IGF-I.b mRNA accumulation decreased 35.8 +/- 1.2% P < 0.05 and IGF-I.a 36 +/- 5.6% P < 0.05; serum IR-IGF-I levels diminished (759 +/- 152 vs. 1327 +/- 67 ng/ml, P < 0.05). Liver IGFBP-3 mRNA accumulation decreased 79 +/- 4.2% P < 0.001. These results indicate that the decrease in GH gene expression and secretion, as well as the expression of genes induced by GH such as IGF-I and IGFBP-3, is due to aging and not to the increase in body weight that takes place with aging.

A mammalian model for Laron syndrome produced by targeted disruption of the mouse growth hormone receptor/binding protein gene (the Laron mouse)

Laron syndrome [growth hormone (GH) insensitivity syndrome] is a hereditary dwarfism resulting from defects in the GH receptor (GHR) gene. GHR deficiency has not been reported in mammals other than humans. Many aspects of GHR dysfunction remain unknown because of ethical and practical limitations in studying humans. To create a mammalian model for this disease, we generated mice bearing a disrupted GHR/binding protein (GHR/BP) gene through a homologous gene targeting approach. Homozygous GHR/BP knockout mice showed severe postnatal growth retardation, proportionate dwarfism, absence of the GHR and GH binding protein, greatly decreased serum insulin-like growth factor I and elevated serum GH concentrations. These characteristics represent the phenotype typical of individuals with Laron syndrome. Animals heterozygous for the GHR/BP defect show only minimal growth impairment but have an intermediate biochemical phenotype, with decreased GHR and GH binding protein expression and slightly diminished insulin-like growth factor I levels. These findings indicate that the GHR/BP-deficient mouse (Laron mouse) is a suitable model for human Laron syndrome that will prove useful for the elucidation of many aspects of GHR/BP function that cannot be obtained in humans.

Insulin-like growth factors in poultry

A large amount of research, primarily in mammals, has defined to a great extent the pleiotropic effects of the IGF system on growth, development, and intermediary metabolism. Similar elucidations in poultry were hindered to some extent by the absence of native peptides (IGF-I and IGF-II) until their purification, followed by the production of recombinant chicken IGFs. In many ways IGF physiology in birds is similar to that in other species, including but not limited to the fact that IGF-I synthesis is both GH- and GH-independent, and that autocrine-paracrine IGF action is evident. However, it is clear that several unique differences in IGF physiology exist between birds and mammals. For example, more IGF is present in the free form in chickens, and the biological responses to the IGFs is different in several metabolic pathways in birds compared to mammals. To date, no unique IGF-II receptor has been identified in birds. Despite an increasing understanding of the IGFs in aves, several important questions remain to be answered. What is the role of IGF-II in embryo development and posthatch growth? Does an IGF-II receptor entity exist in nonmammalian species? How does nutrition affect IGF-I and IGF-II gene expression, and can this information be used to enhance poultry production? What is the biochemical composition of the IGFBPs, and what are their roles in birds? Can the genetic variation present in poultry be used to positively modify IGF gene expression and physiology? How do the IGFs regulate intermediary metabolism? What is the role of the IGFs in the etiology of several disease states associated with rapid growth in poultry, including tibial dyschondroplasia, obesity, ascites, and spiking mortality syndrome? Answers to these questions are relevant to our understanding of the basic mechanisms of IGF physiology as well as possibly assisting in the amelioration of problems found in modern poultry production.

Basal and growth hormone-induced hepatic messenger ribonucleic acid expression of insulin-like growth factor-I (IGF-I) and IGF-binding protein-3 is independent of hyperinsulinemia and increased energy status in the genetically obese Zucker rat

Genetically obese Zucker rats, like obese humans, have normal or elevated circulating insulin-like growth factor-I (IGF-I) levels in the presence of low GH secretion. Hyperinsulinemia, increased energy status, or other nutritional factors associated with obesity could be responsible for these findings directly by increasing hepatic IGF-I production at the transcriptional or posttranscriptional level. Alternatively, circulating IGF-I could be modulated indirectly by affecting its binding proteins. To further elucidate this point, we quantitated hepatic IGF-I, IGF-binding protein-3 (IGFBP-3), and GH receptor messenger RNAs (mRNAs) expression in obese Zucker rats under different serum GH and insulin conditions using lean rats as controls. Eleven-week-old male rats were studied basally (intact) or after hypophysectomy (hx) at 9 weeks. In each condition, animals were killed before or 6 h after one dose of recombinant human GH (1.5 micrograms/g body weight ip). At this time, in addition to the mRNA expression of the above-mentioned genes, body weight, glycemia, insulinemia, serum GH (rat and human), and serum IGF-I levels were determined. Obese Zucker rats were significantly heavier than controls in all the conditions studied and did not show differences in glycemia. Severely hyperinsulinemic intact obese rats (146.9 +/- 14 vs. 46.3 +/- 3 microU/ml, P < 0.001) showed compared with intact lean rats significantly lower serum GH (2.39 +/- 0.9 vs. 4.98 +/- 0.68 ng/ml, P < 0.01), decreased hepatic IGF-I mRNA and IGFBP-3 mRNA accumulation (IGF-Ia: 79 +/- 5.9% vs. 100 +/- 0.9%, P < 0.05; IGF-Ib: 67 +/- 5.5% vs. 100.1 +/- 1.9%, P < 0.001; IGFBP-3: 54.7 +/- 2.75% vs. 100.5 +/- 1.55%, P < 0.001), and similar circulating IGF-I levels (1439 +/- 182 vs. 1516 +/- 121 ng/ml). Under comparable serum GH levels in GH-treated intact, hx, and GH-treated hx animals, hyperinsulinemia and/or increased body weight present in obese rats were not associated with increased hepatic IGF-I and IGFBP-3 mRNA amount. No differences in GH receptor/GH-binding protein mRNAs were found in any experimental condition. These results suggest that in vivo the imbalance of the serum GH/IGF-I axis present in obesity is primarily due to events distal to the hepatic IGF-I and IGFBP-3 mRNAs expression, which is tightly correlated to GH levels.

Altered expression of insulin-like growth factor I and its receptor during multistage carcinogenesis in mouse skin

We examined the possible role of insulin-like growth factor-I (IGF-I) and IGF-I receptor (IGF-Ir) during multistage carcinogenesis in mouse skin. For this purpose, the expression of both IGF-I and IGF-Ir was investigated in mouse skin during tumor promoter treatment and in primary papillomas and squamous cell carcinomas (SCCs) obtained from SENCAR mice treated with standard initiation-promotion regimens. IGF-I transcripts were not detectable or only weakly detectable in normal SENCAR mouse epidermis by northern or reverse transcription (RT)-polymerase chain reaction (PCR) analysis, respectively, whereas IGF-I transcripts (primarily a 7.0-kb transcript) were readily detected in RNA preparations from the dermis by both northern blot analysis and RT-PCR analysis. In contrast, IGF-Ir transcripts were observed in RNA samples from both epidermis and dermis of control SENCAR mice. Single and multiple topical treatments with 3.4 nmol of 12-O-tetradecanoylphorbol-13-acetate (TPA) had no effect on dermal or epidermal IGF-I and IGF-Ir mRNA levels. In contrast, the levels of IGF-I transcripts were elevated (2.5- to 15-fold) in a significant number of mouse skin tumors (71% of all tumors examined). Transcripts of 7.0, 2.5, and 1.3 kb were more consistently overexpressed in skin tumors compared with epidermis, whereas the two smaller transcripts were most consistently overexpressed compared with the dermis. The levels of an 11.0-kb IGF-Ir transcript were also elevated (2.5- to 8-fold) in some papillomas (20%) and SCCs (55%), but the percentage of tumors exhibiting this property (32% of all tumors examined) was lower than the percentage overexpressing IGF-I. These data suggest that altered expression of IGF-I and IGF-Ir may play a role in multistage carcinogenesis in the mouse skin model. The inability of TPA to induce elevated IGF-I or IGF-Ir expression suggests that these changes in skin tumors are coincident with tumor formation and not a direct result of altered epidermal proliferation per se. Altered expression of IGF-I in a high percentage of papillomas may indicate that IGF-I has an important role in the development of autonomous growth in these tumors. The higher percentage of SCCs with altered levels of IGF-Ir mRNA may indicate a role for these changes in the later stages (i.e., tumor progression) of carcinogenesis in this model system.

Differential expression of insulin-like growth factor binding proteins in murine hematopoietic stromal cell lines

The expression of the insulin-like growth factor (IGF) system in the hematopoietic microenvironment during ontogeny was studied utilizing immortalized murine cell lines established from several sites of hematopoiesis. Conditioned media was obtained from tissue cultures of murine yolk sac endoderm and mesoderm, fetal liver and adult bone marrow stromal cell lines. IGF-I and -II were quantified by radioimmunoassay and RT-PCR. The presence of insulin-like growth factor binding proteins (IGFBPs) in conditioned media was determined by Western ligand blot and Western immunoblot. IGF-I and IGF-II were present in conditioned media from every stromal cell line and differential expression of the IGFBPs was found among the hematopoietic sites. Stimulation of the cell lines with interleukin-1 alpha altered the IGFBPs in yolk sac endoderm and bone marrow conditioned media. We report that IGF-I and -II are expressed in stromal cell lines obtained from different ontogenic sites of hematopoiesis and IGFBPs are differentially expressed by these sites. The expression of IGFBPs, but not IGFs, is in part regulated by interleukin-1 alpha.

Increased expression of platelet-derived growth factor A and insulin-like growth factor-I in BAL cells during the development of bleomycin-induced pulmonary fibrosis in mice

Current concepts suggest that macrophages may play a central role in pulmonary fibrosis by virtue of their ability to release a variety of cytokines. In this study, the expression of interleukin (IL)-1 alpha and beta, platelet-derived growth factor (PDGF) A and B, and insulin-like growth factor (IGF) I in BAL cells, which may be involved in fibroblast proliferation, was investigated in murine bleomycin (BLM)-induced pulmonary fibrosis. BAL cells were obtained at 1, 15, and 29 days from Institute for Cancer Research mice after 10 days of intraperitoneal administration of BLM. The relative amounts of cytokine messenger RNA (mRNA) were evaluated by the reverse transcription-polymerase chain reaction method, which simultaneously amplified complementary DNA for cytokines and beta-actin as an internal control. The level of IL-1 beta mRNA in BLM-treated mice was increased 4.5-fold compared with that in saline solution-treated (control) mice 1 day after treatment, while no significant differences were observed between the two groups at 15 and 29 days. The mRNAs of PDGF-A and IGF-I in BLM-treated mice were sustained at levels eightfold and threefold to fourfold, respectively, those of controls over 4 weeks. No significant differences were noted in IL-1 alpha and PDGF-B expression between the two groups. We conclude that IL-1 beta released from macrophages may be important in the early phase of inflammatory responses and that PDGF-A and IGF-I may play important roles in the development of BLM-induced pulmonary fibrosis.

Biochemical characterization of mouse liver IBE1-amide immunoreactivity: limitations of antibody-based approaches for verification of peptide expression

A high titer, specific antiserum, raised against a synthetic analogue of a unique peptide region within the human IGF-IB prohormone, detected specific immunoreactivity in extracts of mouse, chicken, sheep, and human liver. Specificity was confirmed by the ablation of immunoreactivity in the presence of excess synthetic immunogen. Here we report the isolation and characterization of one of the immunoreactive species from an extract of mouse liver: amino acid sequencing revealed that the purified product was 78% identical to the NH2-terminus of the alpha-subunit of mouse hemoglobin. Immunoblot analysis of a commercial preparation of mouse hemoglobin confirmed that the antiserum recognized hemoglobin. Addition of excess synthetic peptide to the antiserum eliminated the immunobinding to hemoglobin. The apparent "specificity" of even affinity-purified antiserum for hemoglobin provides a cautionary note for the interpretation of studies concluding antigen expression based solely on the presence of positive immunoreactivity.

Epidermal growth factor and platelet-derived growth factor regulate the activity of the insulin-like growth factor I gene promoter

The expression of insulin-like growth factor I (IGF-I) is regulated by hormones, oncogenes, and other growth factors, and is markedly decreased or even absent in senescent human diploid fibroblasts. In previous articles, we have reported that the SV40 large T antigen increases the production of IGF-I and that the expression of the IGF-I gene is negatively regulated by an E2F binding site in the IGF-I promoter. We have now investigated the activity of the IGF-I promoter, in response to stimulation of cells by either PDGF or EGF. Both growth factors stimulate the activity of the IGF-I promoter, indicating that they regulate the levels of expression of IGF-I. When the E2F binding sequence in the IGF-I promoter is mutated, the IGF-I promoter is constitutively active and no longer responds to the action of growth factors.

Identifying differences in mRNA expression by representational difference analysis of cDNA

Detection of differentially regulated genes has been severely hampered by technical limitations. In an effort to overcome these problems, the PCR-coupled subtractive process of representational difference analysis (RDA) [Lisitsyn, N. et al. (1993) Science 259, 946-951] has been adapted for use with cDNA. In a model system, RAG-1 and RAG-2, the genes responsible for activating V(D)J recombination, were identified in a genomic transfectant by cDNA RDA in a small fraction of the time taken by conventional means. The system was also modified to eliminate expected difference products to facilitate the identification of novel genes. Additional alterations to the conditions allowed isolation of differentially expressed fragments. Several caffeine up-regulated clones were obtained from the pre-B cell line 1-8, including IGF-1B, and a predicted homologue of the natural killer cell antigen, NKR-P1. The approach was found to be fast, extremely sensitive, reproducible, and predominantly lacked false positives. cDNA RDA has the capacity and adaptability to be applied to a wide range of biological problems, including the study of single gene disorders, characterization of mutant and complemented cell types, developmental or post-event expression time courses, and examination of pathogen-host interactions.

Characterization of a salmon insulin-like growth factor I promoter

We have identified four transcription initiation sites in the salmon insulin-like growth factor I (IGF-I) gene. Use of the most upstream transcription start site generates a minor mRNA species with a 5' untranslated region (UTR) of approximately 450-550 nucleotides, whereas transcription starting at the downstream initiation sites results in more abundant IGF-I mRNAs with 5'-UTRs approximately 250, 245, and 165 nucleotides in length. No consensus TATA box-like elements are present immediately upstream of the most upstream start site identified, nor is this region particularly GC-rich. Transient expression assays, however, demonstrated orientation-dependent promoter activity in a 386-nucleotide-long fragment containing the major downstream transcription start sites. Additionally, reverse transcriptase polymerase chain reaction (RT-PCR) analyses demonstrated tissue and developmental stage-specific use of the various transcription start sites identified.

The receptor, metabolism and effects of androgen in osteoblastic MC3T3-E1 cells

We investigated the androgen receptor (AR), metabolism and effects of androgens in osteoblastic MC3T3-E1 cells. AR was proved as a transcript of a 10-kb mRNA and as a 110-kDa protein. An immunocytochemical study showed that AR was located mainly in the nuclei. Specific binding of [3H]DHT was observed in both the nuclear and cytosol fractions. MC3T3-E1 cells possessed approximately 1190 binding sites per cell and most of the sites (1150 sites) situated in the nucleus. The apparent Kd value in the nuclear fraction was 1.35 nM for [3H]DHT binding, and it was similar to that for [3H]testosterone. In the competition analysis, there was not much difference in the displacement of the [3H]DHT binding from AR between the addition of radioinert DHT and testosterone. In studies of 5 alpha-reductase activity and aromatase activity of the cells, both activities were lower than the respective values in classical androgen target tissues. Androgens stimulated the incorporation of [3H]thymidine into the cell, and DHT and testosterone had a similar potency on the cell proliferation. Thus, these results suggest testosterone itself acts mainly on the osteoblasts without conversion to DHT.

Site of production of IGF1 in the normal and stimulated mouse thyroid

Insulin-like growth factor 1 (IGF1) has emerged as an essential factor in the follicular cell growth response in vitro to TSH, although its source within the thyroid in vivo is not clear. We have studied the localisation of IGF1 mRNA by in situ hybridization using digoxigenin labelled oligoprobes in tissue sections of mouse thyroid. Our results show that in the thyroid IGF1 mRNA is predominantly present in follicular cells and C cells rather than the stroma. Follicular cell levels are higher during postnatal thyroid growth and during the growth response to goitrogen administration, but decrease in the mature animal. This decrease in production is limited to the follicular cells, as IGF1 mRNA is still easily demonstrable in C cells and in the parathyroid. Immunocytochemistry for IGF1 peptide shows a weak and variable follicular cell content in both juvenile and mature mice, but a more uniform distribution during growth in response to a goitrogenic stimulus. These studies show that the follicular cells are the main source of IGF1 in the thyroid, and suggest that the role of IGF1 in follicular cell growth is as an autocrine factor.

Thyroid hormones increase insulin-like growth factor mRNA levels in the clonal osteoblastic cell line MC3T3-E1

Thyroid hormones are known to affect skeletal growth and maturation by influencing both bone resorption and bone formation. Their exact mechanism of action, however, is still unknown. Local factors such as prostaglandins, TGF-beta or IGF-I were suggested to mediate their effects. Thyroid hormones were reported to stimulate expression of IGF-I mRNA in liver and kidney and to increase IGF-I release from bone organ cultures and osteoblast-like cells. Therefore we studied the effect of thyroid hormones on IGF-I mRNA expression in MC3T3-E1 cells. The cells were grown in culture for 5 to 7 days and treated with triiodothyronine (10(-11)-10(-6) M) and thyroxin (10(-6) M) for 1-24 h. Cellular mRNA was isolated and subjected to Northern hybridization. The amount of IGF-I mRNA, which is already expressed in this cell line under control conditions, was markedly enhanced by T3 and T4. This effect was found to be dose-dependent with a maximum at 10(-7) M and could already be seen after 3 h increasing up to 24 h. Our findings indicate that IGF-I expression in osteoblasts is directly regulated by thyroid hormones. We conclude that IGF-I expression belongs to the phenotypic characteristics of mature osteoblasts, and that thyroid hormones play an important role in differentiation of MC3T3-E1 cells along the osteoblastic lineage.

Riboprobe expression cassettes for measuring IGF-I, beta-actin and glyceraldehyde 3-phosphate dehydrogenase transcripts

The development of riboprobe expression cassettes for phosphorimager-based quantitation of steady-state transcripts for three different genes using solution hybridization, RNase protection assays is described. Glyceraldehyde 3-phosphate dehydrogenase (GAPDH) and beta-actin genes are widely used as reporter genes to estimate the amount and integrity of RNA as well as for comparing gene expression among different tissues. To directly compare expression of these two genes in lymphoid tissue and liver, cDNA fragments of beta-actin and GAPDH from both mice and rats were generated by RT-PCR and cloned together into pGEM1 under control of the T7 RNA polymerase promoter. Antisense transcripts from this fusion construct protected the appropriate-sized fragments of beta-actin (115 nt) and GAPDH (214 nt) in RNA isolated from rat spleen, thymus and liver. Expression of GAPDH transcripts was less variable across tissues because this mRNA was only two-fold lower in liver as compared to either thymus or spleen, whereas expression of beta-actin transcripts was eight-fold lower in liver than in these tissues. Two other riboprobe expression cassettes (IGF-I/actin) were constructed by ligating a cDNA fragment of mouse or rat beta-actin that would protect 115 nt to either a mouse or rat IGF-I genomic DNA fragment containing 182 bp of exon 4. These mouse and rat IGF-I/actin riboprobes were used to conclusively demonstrate that rat CSF-1-derived bone marrow macrophages, mouse elicited peritoneal macrophages and the murine PU5-1R macrophage cell line synthesize abundant transcripts for both IGF-I and beta-actin. However, the mouse M1 progenitor myeloid cell line does not express RNA for IGF-I, as demonstrated by the absence of protected transcripts for IGF-I in the presence of abundant protected transcripts for beta-actin. Phosphorimager scanning of the gels revealed that macrophages of both mice and rats express IGF-I transcripts at a level of 60-100% of those found in liver. These data show that a single riboprobe can be developed to generate multigene antisense RNAs that can then be used to quantitatively compare IGF-I transcripts in macrophages and other tissues to an internal standard, with GAPDH transcripts being less variable among tissues than those for beta-actin. This approach should be broadly applicable for measuring a variety of markers of cellular activation.

Effects of interleukin-1 beta on insulin-like growth factor-I autocrine/paracrine axis in cultured rat articular chondrocytes

OBJECTIVE

To clarify the interaction of tissue destruction and repair of articular cartilage during inflammation, the effects of interleukin-1 beta (IL-1 beta) on the expression of insulin-like growth factor I (IGF-I), its receptor, and its binding proteins were examined.

METHODS

Articular chondrocytes from five week rats were cultured in serum free medium treated with IL-1 beta (1-100 U/ml) for 24 hours. The concentration of IGF-1 in the conditioned medium was measured by RIA, and IGFBP were analysed by immunoligand blotting method. IGF-I receptors were also examined by [125I]IGF-I binding study.

RESULTS

IL-1 beta induced the secretion of IGF-I and IGF-binding protein in chondrocytes; this was not inhibited by indomethacin (5 micrograms/ml). IL-1 beta also increased the number of IGF-I receptors but had no effect on receptor affinity. IL-1 beta inhibited chondrocyte proliferation, while exogenous IGF-I and growth hormone stimulated chondrocyte cell growth. IL-1 beta did not change IGF-I mRNA levels.

CONCLUSION

IL-1 beta up-regulated the IGF-I autocrine/paracrine axis in cultured articular chondrocytes. These observations provide insight into the critical role played by IL-1 beta in tissue destruction and repair, and into the direct interaction between cytokines and growth factors associated with inflammatory arthropathy.

Temporal pattern of IGF-I expression during mouse preimplantation embryogenesis

Although mouse preimplantation embryos express transcripts for the insulin-like growth factor-I receptor (IGF-IR), IGF-I transcripts were not detected by reverse transcription-PCR (RT-PCR) at any stage of preimplantation development in a previous study (Rappolee et al., Genes Dev 6:939-952, 1992). We report that IGF-I transcripts are detected in the preimplantation embryo by RT-PCR and describe the temporal pattern of expression of this transcript from the oocyte to blastocyst stages; the level declines from the oocyte to 8-cell embryo and then increases from the 8-cell to blastocyst stages. An explanation is offered to account for the differences in detecting the IGF-I transcript, and the results are discussed in the context of an autocrine/paracrine IGF-I circuit in the preimplantation mouse embryo.

Structure of the chum salmon insulin-like growth factor I gene

Insulin-like growth factor I (IGF-I) plays a major role in development and metabolism. Currently, the cDNA-derived primary structure of IGF-I is known for some mammals and for chicken, frog, and salmon. Additionally, the organization of the human, rat, and chicken IGF-I genes has been established. The investigation of IGF-I gene structure in fish would extend the evolutionary picture for this hormone and facilitate our understanding of the features of the IGF-I gene that are common to all vertebrate species. The cloned chum salmon IGF-I gene appears to be much more compact than the mammalian and avian genes, being less than 20 kb in length. As in other species, however, the mature IGF-I peptide appears to consist of 70 amino acids and is encoded by exons 2 and 3. Intriguingly, exon 1-encoded 5'-untranslated region sequences are highly conserved, while the coding sequences at the 3' end of the same exon are less conserved. The amino terminus of the signal peptide is four amino acids shorter than in the mammalian and avian peptides. The end of the B domain, the C, A, and D domains, and the first part of the E peptide are encoded by exon 3, but the exon 3-encoded E peptide sequence is 27 amino acids longer than in other species. These extra 27 amino acids, encoded by both coho and chum salmon cDNAs, may be deleted by alternative splicing, as suggested from the sequence of a coho salmon IGF-I cDNA.(ABSTRACT TRUNCATED AT 250 WORDS)

Insulin-like growth factors

The purpose of this review has been to emphasize, in general terms, the major aspects of the structure, expression, and regulation of the IGF-I and IGF-II genes. The complex organization of these genes provides ample opportunities for control of gene expression at multiple levels. It is important to realize that regulation at one level can influence regulation at a different level. While such regulatory interactions are characteristic of both the IGF-I and IGF-II genes, they are particularly evident in the case of IGF-I gene expression. For example, the choice of transcription start site influences the length and the sequence of the 5'-UTR, which can influence mRNA translatability and prepeptide sequence, which may influence the amounts of protein produced and, potentially, the intracellular processing and secretion of the final gene product, the mature hormone. Another example is provided by the alternative splicing of E-peptide-encoding exons, which determines the primary structure of the prohormone, which could influence its processing, stability, or function. Thus, this complex gene organization may reflect the need to carefully control, through a multilevel process, the synthesis, processing, and secretion of these important regulatory peptides.

Sequence of a cDNA encoding dog insulin-like growth factor I

Polymerase chain reaction amplification of a cDNA derived from dog left ventricular myocardium, using primers specific for rat insulin-like growth factor I (IGFI), exons 3 and 6, yielded the dog clone, IGFI5.1. This clone includes the signal peptide sequence, the entire coding sequence for mature dog IGFI and the C-terminal extension sequence. By analogy with the organization of the rat and human IGFI genes which encode two extension peptides, we have termed this cDNA, dog IGFIa. The deduced amino acid sequence of mature dog IGFI is identical to that of human IGFI.

Effects of 9-ene-tetrahydrocannabinol on expression of beta-type transforming growth factors, insulin-like growth factor-I and c-myc genes in the mouse uterus

Effects of cannabinoid on expression of beta-type transforming growth factors (TGF-beta 1, -beta 2 and -beta 3), insulin-like growth factor-I (IGF-I) and c-myc genes in the uteri of adult ovariectomized mice were examined using Northern blot hybridization. Mice were exposed to 9-ene-tetrahydrocannabinol (THC) alone or in combination with an injection of estradiol-17 beta (E2) and/or progesterone (P4), and uteri were analyzed at various times thereafter. TGF-beta isoform messenger RNAs (mRNAs) persisted in ovariectomized uteri and their levels were not altered after THC treatment, whereas an injection of E2 caused a modest increase in TGF-beta 1 and -beta 3 mRNA levels at 24 h. Imposition of THC treatment advanced the stimulatory effects of E2 by changing the timing for the peak of TGF-beta 3 mRNA levels to 12 h. In comparison, E2 treatment substantially elevated the levels of TGF-beta 2 mRNA at 6 h, and THC potentiated this E2 response without affecting the timing for the response. Imposition of P4 treatment did not antagonize any of these responses. P4 treatment alone or with THC had insignificant effects on mRNA levels for these TGF-beta isoforms. Uterine levels of IGF-I and c-myc mRNAs were low in ovariectomized mice and THC did not alter these mRNA levels. In contrast, E2 treatment induced a rapid, but transient, increase in IGF-I and c-myc mRNAs, and THC antagonized the rapid c-myc mRNA response and altered the timing of the IGF-I mRNA response. P4 treatment alone also caused the transient induction of these mRNAs, but THC failed to antagonize these effects. An injection of P4 plus E2 resulted in further modest increases in IGF-I and c-myc mRNA levels as compared to E2 or P4 treatment alone. However, THC did not antagonize these transient stimulatory effects of the combined ovarian steroids. The data suggest that THC should not be classified as estrogenic or antiestrogenic. However, this compound can modulate (potentiate, antagonize and/or alter timing) the effects of ovarian steroids on uterine gene expression.

The growth-stimulatory effect of simian virus 40 T antigen requires the interaction of insulinlike growth factor 1 with its receptor

We have used a plasmid expressing a temperature-sensitive (ts) mutant of simian virus 40 (SV40) T antigen, stably transfected into 3T3 cells, to study the role of insulinlike growth factor 1 (IGF-1) and its receptor in T-antigen-mediated growth. While 3T3 cells do not grow in serum-free medium, in 1% serum, or with the sole addition of either platelet-derived growth factor (PDGF) or IGF-1, cells expressing the tsA T antigen (BALB 58 cells) grow at 34 degrees C in either PDGF or 1% serum but not in IGF-1. At the restrictive temperature (39.6 degrees C), these cells can only grow in 10% serum. We show that BALB 58 cells, at 34 degrees C, have a markedly increased expression of IGF-1 and IGF-1 mRNA and that their growth in 1% serum (at 34 degrees C) is inhibited by an antisense oligodeoxynucleotide to the IGF-1 receptor RNA. When this tsA plasmid is stably transfected into cells constitutively overexpressing the human IGF-1 receptor cDNA, the resulting cell lines show a constitutively phosphorylated IGF-1 receptor and grow in serum-free medium at 34 degrees C (but not at 39.6 degrees C). A functional SV40 T antigen also increases the expression of a plasmid in which the reporter luciferase gene is under the control of a rat IGF-1 promoter. We conclude (i) that the SV40 T antigen induces the expression of IGF-1 and IGF-1 mRNA, at least in part by a transcriptional mechanism, thus altering the growth factors requirements, and (ii) that, in BALB/c3t3 cells, the SV40 T antigen necessitates a functional IGF-1 receptor for its growth-stimulating effect in low serum (or PDGF).

The growth-stimulatory effect of simian virus 40 T antigen requires the interaction of insulinlike growth factor 1 with its receptor

We have used a plasmid expressing a temperature-sensitive (ts) mutant of simian virus 40 (SV40) T antigen, stably transfected into 3T3 cells, to study the role of insulinlike growth factor 1 (IGF-1) and its receptor in T-antigen-mediated growth. While 3T3 cells do not grow in serum-free medium, in 1% serum, or with the sole addition of either platelet-derived growth factor (PDGF) or IGF-1, cells expressing the tsA T antigen (BALB 58 cells) grow at 34 degrees C in either PDGF or 1% serum but not in IGF-1. At the restrictive temperature (39.6 degrees C), these cells can only grow in 10% serum. We show that BALB 58 cells, at 34 degrees C, have a markedly increased expression of IGF-1 and IGF-1 mRNA and that their growth in 1% serum (at 34 degrees C) is inhibited by an antisense oligodeoxynucleotide to the IGF-1 receptor RNA. When this tsA plasmid is stably transfected into cells constitutively overexpressing the human IGF-1 receptor cDNA, the resulting cell lines show a constitutively phosphorylated IGF-1 receptor and grow in serum-free medium at 34 degrees C (but not at 39.6 degrees C). A functional SV40 T antigen also increases the expression of a plasmid in which the reporter luciferase gene is under the control of a rat IGF-1 promoter. We conclude (i) that the SV40 T antigen induces the expression of IGF-1 and IGF-1 mRNA, at least in part by a transcriptional mechanism, thus altering the growth factors requirements, and (ii) that, in BALB/c3t3 cells, the SV40 T antigen necessitates a functional IGF-1 receptor for its growth-stimulating effect in low serum (or PDGF).

Roles of insulinlike growth factor 1 (IGF-1) and the IGF-1 receptor in epidermal growth factor-stimulated growth of 3T3 cells

BALB/c3T3 cells are exquisitely growth regulated and require platelet-derived growth factor, epidermal growth factor (EGF), and insulinlike growth factor 1 (IGF-1) for growth. When BALB/c3T3 cells are transfected with plasmids constitutively expressing both EGF and the human IGF-1 receptor mRNAs, the cells are capable of growing in serum-free medium without the addition of any exogenous growth factor. These cells, called p5 cells, can grow for prolonged periods in serum-free medium. BALB/c3T3 cells transfected with only the IGF-1 receptor expression plasmid (p6 cells) do not grow in serum-free medium but do grow if IGF-1 (or insulin in supraphysiological concentrations) is added. p6 cells also grow in response to EGF, confirming that the combination of EGF and an overexpressed IGF-1 receptor is sufficient for the growth of 3T3 cells. We have found that in EGF-stimulated p6 cells there is an increase in the expression of IGF-1 mRNA, that IGF-1 is secreted into the medium, and that the growth of p5 cells and EGF-stimulated p6 cells is inhibited by exposure to antisense oligodeoxynucleotides to IGF-1 receptor RNA. Finally, while cells constitutively expressing both EGF and EGF receptor RNAs grow, albeit modestly, in serum-free medium, their growth is also inhibited by an antisense oligodeoxynucleotide to IGF-1 receptor RNA. In contrast, in cells overexpressing the IGF-1 receptor, IGF-1-mediated cell growth occurs independently of the platelet-derived growth factor and EGF receptors (Z. Pietrzkowski, R. Lammers, G. Carpenter, A. M. Soderquist, M. Limardo, P. D. Phillips, A. Ullrich, and R. Baserga, Cell Growth Differ. 3:199-205, 1992, and this paper). These data indicate that an important role for EGF is participation in the activation of an autocrine loop based on the IGF-1-IGF-1 receptor interaction, which is obligatory for the proliferation of 3T3 cells.

Roles of insulinlike growth factor 1 (IGF-1) and the IGF-1 receptor in epidermal growth factor-stimulated growth of 3T3 cells

BALB/c3T3 cells are exquisitely growth regulated and require platelet-derived growth factor, epidermal growth factor (EGF), and insulinlike growth factor 1 (IGF-1) for growth. When BALB/c3T3 cells are transfected with plasmids constitutively expressing both EGF and the human IGF-1 receptor mRNAs, the cells are capable of growing in serum-free medium without the addition of any exogenous growth factor. These cells, called p5 cells, can grow for prolonged periods in serum-free medium. BALB/c3T3 cells transfected with only the IGF-1 receptor expression plasmid (p6 cells) do not grow in serum-free medium but do grow if IGF-1 (or insulin in supraphysiological concentrations) is added. p6 cells also grow in response to EGF, confirming that the combination of EGF and an overexpressed IGF-1 receptor is sufficient for the growth of 3T3 cells. We have found that in EGF-stimulated p6 cells there is an increase in the expression of IGF-1 mRNA, that IGF-1 is secreted into the medium, and that the growth of p5 cells and EGF-stimulated p6 cells is inhibited by exposure to antisense oligodeoxynucleotides to IGF-1 receptor RNA. Finally, while cells constitutively expressing both EGF and EGF receptor RNAs grow, albeit modestly, in serum-free medium, their growth is also inhibited by an antisense oligodeoxynucleotide to IGF-1 receptor RNA. In contrast, in cells overexpressing the IGF-1 receptor, IGF-1-mediated cell growth occurs independently of the platelet-derived growth factor and EGF receptors (Z. Pietrzkowski, R. Lammers, G. Carpenter, A. M. Soderquist, M. Limardo, P. D. Phillips, A. Ullrich, and R. Baserga, Cell Growth Differ. 3:199-205, 1992, and this paper). These data indicate that an important role for EGF is participation in the activation of an autocrine loop based on the IGF-1-IGF-1 receptor interaction, which is obligatory for the proliferation of 3T3 cells.

Gonadotropins induce accumulation of insulin-like growth factor I mRNA in pig granulosa cells in vitro

Pig granulosa cells have been shown to synthesize insulin-like growth factor (IGF) I peptide in vitro, and this expression is regulated by gonadotropins via the cAMP pathway. By hybridizing an IGF I cDNA probe with total RNA isolated from pig granulosa cells cultured in vitro, we show that these cells contain two IGF I transcripts of about 0.9 kb and 9 kb in size. Treatment of the cells with gonadotropins (follicle-stimulating hormone, luteinizing hormone) or cAMP agonists (dibutyryl-cAMP, forskolin) induces an accumulation of the transcripts which can be abolished by transcriptional inhibitors, but not by translational inhibitors. We thus provide new evidence that pig granulosa cells are a site of IGF I synthesis, and we conclude that (1) gonadotropins increase IGF I mRNA levels; (2) the accumulation of IGF I mRNA results from an increased transcription; (3) the stimulation of IGF I gene transcription does not require ongoing protein synthesis; (4) these effects of follicle-stimulating hormone can be mimicked by cAMP agonists.

Insulin-like growth factor II acts through an endogenous growth pathway regulated by imprinting in early mouse embryos

We present evidence that insulin-like growth factor II (IGF-II) mediates growth in early mouse embryos and forms a pathway in which imprinted genes influence development during preimplantation stages. mRNA and protein for IGF-II were expressed in preimplantation mouse embryos, but the related factors IGF-I and insulin were not. IGF-I and insulin receptors and the IGF-II/mannose-6-phosphate receptor were expressed. Exogenous IGF-II or IGF-I increased the cell number in cultured blastocysts, but a mutant form of IGF-II that strongly binds only the IGF-II receptor did not. Reduction of IGF-II expression by antisense IGF-II oligonucleotides decreased the rate of progression to the blastocyst stage and decreased the cell number in blastocysts. Preimplantation parthenogenetic mouse embryos expressed mRNA for the IGF-II receptor but not for either IGF-II ligand or the IGF-I receptor, indicating that the latter genes are not expressed when inherited maternally. These data imply that some growth factors and receptors, regulated by genomic imprinting, may control cell proliferation from the earliest stages of embryonic development.

Temporal and quantitative analysis of myogenic regulatory and growth factor gene expression in the developing mouse embryo

Using a reverse transcription/polymerase chain reaction method, the temporal pattern of expression of the myogenic regulatory genes (myf5, myogenin, MRF4, myo D) was quantitated in developing mouse muscle (whole embryo: 6.5 to 12.5 days postcoitum (dpc); front limb buds: 9.5 to 12.5 dpc; hind limb buds: 11.5 to 14.5 dpc) and related to expression of TGF-beta 1, b-FGF, IGF-I, and IGF-II. Myf5 was the first myogenic regulatory factor to appear in both the whole embryo and front limb bud, with expression evident 7.5 and 9.5 dpc, respectively. A transient peak of MRF4 expression occurred 10.5 dpc in both the whole embryo and the front limb bud. Myogenin and myo D expression in the whole embryo was detected 8.5 and 9.5 dpc, respectively. In the front limb bud myogenin and myo D expression was not detected until 10.5 dpc. In the hind limb bud myf5, myogenin, and MRF4 expression was detected 11.5 dpc. Myo D expression was not detected until 12.5 dpc. With respect to growth factor expression, in the front limb bud TGF-beta 1, IGF-I, and IGF-II were evident 9.5 dpc, while bFGF was not detected until 10.5 dpc. In the hind limb bud TGF-beta 1, bFGF, IGF-I, and IGF-II expression was detected 11.5 dpc. These results show that in both the whole embryo and limb buds, all four myogenic regulatory factors are involved in the initiation of the myogenic program. We also show myf5 expression in the 9.5-dpc front limb bud, suggesting its expression in the somite-derived migrating muscle precursor cells. Correlations between growth factor-mediated myoblast proliferation and myogenic differentiation are discussed.

Expression of IGF-1 mRNA in the murine subventricular zone during postnatal development

Insulin-like growth factor-1 (IGF-1) stimulates the proliferation and maturation of neuroglia in vitro. To further investigate its role in gliogenesis, in situ hybridization was utilized to determine whether IGF-1 mRNA was expressed in the subventricular zone (SVZ) of the postnatal mouse forebrain. The SVZ is a transient germinal zone and in the neonate is the principle source of oligodendroglia for myelinating fiber tracts of the forebrain. Strong hybridization signal was detected over cells in the SVZ at postnatal day (PND) 4, the earliest time point examined. Positive signal persisted in the SVZ at PND 8, however, the number of IGF-1-labeled cells declined rapidly during the second postnatal week. IGF-1 mRNA was not uniformly distributed throughout the SVZ and the majority of labeled cells were located within its so-called 'border' region. In contrast to the SVZ, IGF-1 mRNA-expressing cells were only rarely found in forebrain fiber tracts. IGF-1 transcripts were not detected in ependymal lining or choroid plexus of the lateral ventricle. In light of its known gliotrophic activity, the localization of IGF-1 mRNA in the SVZ suggests that locally produced IGF-1 may act as a mitogen or differentiation-inducing agent during gliogenesis.