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PubMed1994

Hormonal regulation of insulin-like growth factor II and insulin-like growth factor binding protein expression by breast cancer cells in vivo: evidence for stromal epithelial interactions.

Insulin-like growth factors (IGFs) I and II are potent mitogens for breast cancer cells. Their proliferative activity is likely to be influenced by their binding proteins (IGFBPs), a family of newly identified proteins. We report here on the in vivo hormonal regulation of mRNAs for IGF-II and IGFBPs in the N-nitrosomethylurea-induced rat mammary tumor, a well-established model of hormone-responsive mammary cancer. IGF-II mRNA levels tended to decrease in regressing tumors following ovariectomy, and they markedly increased upon reactivation of tumor growth with hormone repletion. Ovariectomy induced a drastic increase in IG-FBP-6 mRNA which was reversible with hormone repletion. Similar but more modest changes were observed with IGFBP-2 mRNA. In contrast, IGFBP-3 and IGFBP-4 mRNAs tended to decrease with ovariectomy and increase with hormone repletion. These latter effects, however, were modest, variable, and not statistically significant. In situ hybridization analysis revealed that IGF-II, IGFBP-5, and IGFBP-6 mRNAs were localized in the stromal component of the tumor, whereas IGFBP-2 mRNA was expressed by epithelial cells. We conclude that hormonal regulation of IGFBP expression is heterogeneous, thus suggesting divergent biological functions for these peptides. Our data also emphasize the importance of potential stromal-epithelial interactions in the control of breast cancer cell proliferation by IGFs.

Animals↗

PubMed1999

Frequent factor II G20210A mutation in idiopathic portal vein thrombosis.

BACKGROUND & AIMS: Despite extensive investigations of portal vein thrombosis, no underlying cause is identifiable in up to 30% of patients. A recently described mutation of the prothrombin gene at nucleotide position 20210 is associated with history of venous thrombosis and was assessed in this study. METHODS: We compared the frequency of factor II G20210A and factor V G1691A (factor V Leiden) mutations in 10 patients with idiopathic portal vein thrombosis, 10 patients with nonidiopathic portal vein thrombosis, 60 patients with deep vein thrombosis of the legs, and 42 control subjects. RESULTS: The frequency of factor II G20210A mutation was increased in patients with idiopathic portal vein thrombosis (40.0%; confidence interval, 3.1%-76.9%) compared with controls (4.8%; confidence interval, 0%-11.5%) or patients with nonidiopathic portal vein thrombosis or deep vein thrombosis (P = 0.0001). In contrast, the frequency of the factor V G1691A mutation was similar in subjects with portal vein thrombosis and in controls but was increased in patients with deep vein thrombosis (P = 0.0001). CONCLUSIONS: The factor II G20210A mutation is frequent in patients with idiopathic portal vein thrombosis and should therefore be assessed under this circumstance.

Adult↗

PubMed1990

Immunoreactive insulin-like growth factor II in urine.

Insulin-like growth factor II and insulin-like growth factor binding protein-1 were identified and quantified in the urine of 23 healthy subjects between 17 and 76 years of age. IGF-II was measured after separation by gel chromatography at low pH and compared with IGF-I levels in the same samples, whereas IGF binding protein-1 was measured in dialysed urine. Urinary IGF-II was found at much higher concentrations than IGF-I (mean +/- SEM: 717 +/- 69 vs 110 +/- 5 ng/mmol creatinine). The chromatographic profile indicates that pro-IGF-II may also be present. The concentrations of IGF-II appear to be less variable than the other reported parameters. The mean IGF binding protein-1 concentrations in these urine samples was 414 +/- 83 ng/mmol creatinine. IGFs in the urine are in part bound to binding proteins.

Adolescent↗

PubMed1987

The major erythrotropin of bovine Cohn fraction V has the N-terminal sequence of insulin-like growth factor II with isoleucine at position 35.

The major erythrotropin-like factor of bovine Cohn Fraction V has been isolated from commercial albumin preparations by reversed-phase HPLC. The N-terminal sequence of the major fraction with erythrotropin-like activity is practically identical to the sequence of bovine insulin-like growth factor II. Within the first 45 amino acids, the only difference was the presence of an isoleucine instead of a serine at amino acid 35. This substitution may affect the immunoreactivity of this peptide using antibodies against bovine or human insulin-like growth factor II.

Amino Acid Sequence↗

PubMed1982

Use of chromogenic peptide substrates in the determination of clotting factors II, VII, IX and X in normal plasma and in plasma of patients treated with oral anticoagulants.

Spectrophotometric methods were used to assay the clotting factors II, VII, IX and X in plasma of 33 subjectively healthy human donors and in plasma of 98 patients receiving long-term oral anticoagulant therapy. In 33 normal subjects the interindividual variations in the plasma activities of the clotting factors II, VII, IX and X are respectively 12.2, 21.4, 11.0 and 15.0%. After correction for the assay variations the remaining biological variations are respectively 11.7, 21.2, 9.7 and 14.8%. Plasma from 98 patients receiving long-term anticoagulant therapy was assayed with 'Thrombotest', a clotting test in whole blood introduced by Owren and in these plasmas the activity of each of the vitamin K-dependent factors was assayed with spectrophotometric methods. For the clotting factors IX and VII, novel spectrophotometric methods were applied and the plasma activities thus measured were compared to results obtained with factor IX and VII clotting assays. Chromogenic activities of the different factors were correlated among each other and with 1/Thrombotest values. When the therapeutic range for Thrombotest values is set between 5 and 12.5% the corresponding therapeutic ranges for the activity of the factors II, VII, IX and X are respectively 12.6-36.1, 27.0-52.3, 23.1-49.3 and 18.9-36.2% (expressed as a percentage of the activity in normal pool plasma). The chromogenic assays for the factors II, VII, IX and X provide the same information on the therapeutic state of the patients in respectively 86.7, 78.6, 81.6 and 89.8% of the cases. Finally we discuss the suitability of the different assays to monitor oral anticoagulant therapy.

Administration, Oral↗

PubMed1989

Insulin-like growth factor-II (IGF-II) inhibits both the cellular uptake of beta-galactosidase and the binding of beta-galactosidase to purified IGF-II/mannose 6-phosphate receptor.

The insulin-like growth factor-II/mannose 6-phosphate receptor which targets acid hydrolases to lysosomes, has two different binding sites, one for the mannose 6-phosphate (Man-6-P) recognition marker on lysosomal enzymes and the other for insulin-like growth factor-II (IGF-II). We have asked whether IGF-II can regulate the cellular uptake of the lysosomal enzyme 125I-beta-galactosidase by modulating the binding of 125I-beta-galactosidase to the IGF-II/Man-6-P receptor. We first isolated high affinity 125I-beta-galactosidase by affinity chromatography on an IGF-II/Man-6-P receptor-Sepharose column. Specific uptake (mannose 6-phosphate-inhibitable) of 125I-beta-galactosidase in BRL 3A2 rat liver cells and in rat C6 glial cells was 3.7-4.8 and 4.0-8.0% of added tracer, respectively. The cell-associated 125I-beta-galactosidase in the uptake experiments largely represented internalized radioligand as measured by acid or mannose 6-phosphate washing. The uptake of 125I-beta-galactosidase was inhibited by an antiserum (No. 3637) specific for the IGF-II/Man-6-P receptor. Low concentrations of IGF-II also inhibited the uptake of 125I-beta-galactosidase. Maximal concentrations of IGF-II inhibited uptake by 73 +/- 8% (mean +/- S.D.) in C6 cells and by 77 +/- 6% in BRL 3A2 cells compared to the level of inhibition by mannose 6-phosphate. The relative potency of IGF-II, IGF-I, and insulin (IGF-II much greater than IGF-I; insulin, inactive) were characteristic of the relative affinities of the ligands for the IGF-II/Man-6-P receptor. IGF-II also partially inhibited the binding of 125I-beta-galactosidase to C6 and BRL 3A2 cells at 4 degrees C and inhibited the binding to highly purified IGF-II/Man-6-P receptor by 58 +/- 14%. We conclude that IGF-II inhibits the cellular uptake of 125I-beta-galactosidase and that this inhibition is partly explained by the ability of IGF-II to inhibit binding of 125I-beta-galactosidase to the IGF-II/Man-6-P receptor.

Animals↗

PubMed2005

The role of thrombofilia related to Factor V Leiden and Factor II G20210A mutations in recurrent abortions.

OBJECTIVE: To study, the impact of thrombophilia caused by Factor V, Factor ll G20210A mutations on recurrent abortions, the prevelance of Factor V Leiden and Factor II G20210A mutation in patients with habitual abortions. METHODS: Forty one patients with a diagnosis of habitual abortion were enrolled in the study. Control group consisted of 50 women without a history of poor obstetric outcome. 10 ml. peripheral venous blood was taken from study and control groups and transferred to EDTA tubes, and were tested for Factor V Leiden and Factor II G20210A mutations by PCR in genetics laboratory. RESULTS: Phenotypes of 91 cases were determined by PCR for Factor V Leiden. It was established that of 41 patients in the study group, 31 (75.6%) had GG genotype, 9 (22%) had GA genotype and 1 (2.4%) had AA genotype. In the control group, 45 (90%) of 50 women had GG genotype and 5 (10%) had GA genotype. A allele carrier status was found to be 24.4% in study group and 10% in the control group. The difference between them was not statistically significant (p = 0.06). CONCLUSIONS: The results obtained from patients and control group have no difference in Factor V Leiden and Factor II G20210A mutations.These results suggest that mutations have no role in etiology of 1. and 2. trimester recurrent abortions.

Abortion, Habitual↗

PubMed2006

Mannose-6-phosphate/insulin-like growth factor II receptor expression and tumor development.

The mannose-6-phosphate/insulin-like growth factor II receptor (M6P/IGF-IIR) is a multi-functional transmembrane glycoprotein whose major function is to bind and transport M6P-bearing glycoproteins from the trans-Golgi network or the cell surface to lysosomes. The cell surface M6P/IGF-IIR also bind and internalizes the insulin-like growth factor II. The receptor gene is considered a "candidate" tumor suppressor gene. The phenotypic consequences of loss of M6P/IGF-IIR through somatic mutation are potentially very complex since M6P/IGF-IIR has a number of roles in cellular physiology. Loss of function mutations in M6P/IGF-IIR gene could contribute to multi-step carcinogenesis. In the light of the multi-functional cellular potential roles of the M6P/IGF-IIR the purpose of this review is to highlight some recent data concerning its normal functions and the potential role of its loss in tumor pathophysiology with the aim to try to clarify the possible underlying mechanisms of its involvement in tumor development.

Animals↗

PubMed1990

Chemical and biological characterization of chicken insulin-like growth factor-II.

Chicken insulin-like growth factor-II (cIGF-II) has been characterized by amino acid sequencing, by its receptor and binding protein interactions and by its biological activities in cultured cells in order to help define the significance of the peptide in the growth process. Chicken IGF-II has an N-terminal region and several amino acid substitutions in the mid-peptide region that differ from the mammalian growth factor. Nevertheless, cIGF-II was indistinguishable from ovine IGF-II in all assay systems, including those involving chicken receptors and chicken binding proteins. Thus the amino acid substitutions did not modify the biological activities. In chick embryo fibroblasts, labelled bovine IGF-II or cIGF-II bound to a receptor with size and specificity properties expected for a type 1 IGF receptor, except that IGF-I competition for binding was less than IGF-II competition. No evidence for a type 2 receptor was obtained. The relatively lower biological activity of IGF-I compared with IGF-II in chick embryo fibroblasts contrasts with the much higher potency of IGF-I in rat L6 myoblasts. This difference can be explained by a combination of an inhibitory, IGF-II-specific binding protein produced only by the rat cells as well as the unusual receptor specificity of the chicken cells.

Amino Acid Sequence↗

PubMed1999

Insulin-like growth factor-II, phosphatidylinositol 3-kinase, nuclear factor-kappaB and inducible nitric-oxide synthase define a common myogenic signaling pathway.

Insulin-like growth factors (IGFs) are potent inducers of skeletal muscle differentiation and phosphatidylinositol (PI) 3-kinase activity is essential for this process. Here we show that IGF-II induces nuclear factor-kappaB (NF-kappaB) and nitric-oxide synthase (NOS) activities downstream from PI 3-kinase and that these events are critical for myogenesis. Differentiation of rat L6E9 myoblasts with IGF-II transiently induced NF-kappaB DNA binding activity, inducible nitric-oxide synthase (iNOS) expression, and nitric oxide (NO) production. IGF-II-induced iNOS expression and NO production were blocked by NF-kappaB inhibition. Both NF-kappaB and NOS activities were essential for IGF-II-induced terminal differentiation (myotube formation and expression of skeletal muscle proteins: myosin heavy chain, GLUT 4, and caveolin 3), which was totally blocked by NF-kappaB or NOS inhibitors in rat and human myoblasts. Moreover, the NOS substrate L-Arg induced myogenesis in the absence of IGFs in both rat and human myoblasts, and this effect was blocked by NOS inhibition. Regarding the mechanisms involved in IGF-II activation of NF-kappaB, PI 3-kinase inhibition prevented NF-kappaB activation, iNOS expression, and NO production. Moreover, IGF-II induced, through a PI 3-kinase-dependent pathway, a decrease in IkappaB-alpha protein content that correlated with a decrease in the amount of IkappaB-alpha associated with p65 NF-kappaB.

Animals↗

PubMed1995

Insulin-like growth factor-II expression in carcinoma in colon cell lines: implications for autocrine actions.

BACKGROUND: In the gastrointestinal tract, insulin-like growth factor-II (IGF-II) messenger RNA (mRNA) is localized mainly in mesenchymal cells, and is more abundant in the fetus than in the adult. The purposes of this study are to characterize the gene expression of IGF-II at the mRNA and protein level in seven different epithelial cell lines derived from colon carcinomas and to determine the action of IGF-II and IGF-receptors on a colon carcinoma cell line. STUDY DESIGN: Insulin-like growth factor-II mRNAs were examined by Northern analysis; conditioned media from colon carcinoma cells were concentrated, chromatographed, and examined by a specific IGF-II radioreceptor assay. Insulin-like growth factor receptors were examined by radioligand binding assays. The mitogenic role of IGF-II was determined by a 3-(4,5-dimethylthiazol-2yl)-2,5-diphenyltetrazolium bromide assay. RESULTS: Multiple sizes of IGF-II mRNAs were expressed in all colon carcinoma cell lines tested (six human cell lines: HCT116, COLO 205, COLO 320 DM, LoVo, DLD-1, and HT29, and one mouse cell line: MC-26). In the conditioned media of COLO 205 and HCT116 cells, 7.5 kilodaltons IGF-II and high molecular form (IGF-II and IGF binding protein complex) were detected. Both Type I and Type II IGF receptors were present on COLO 205 cells whose growth was stimulated by IGF-II. Addition of anti-IGF-I receptor and anti-IGF-II antibody in the cell culture significantly depressed growth of the COLO 205 cell line in the presence or absence of exogenous IGF-II. CONCLUSIONS: Insulin-like growth factor-II mRNAs are expressed in human and mouse colon carcinoma cell lines, which may induce production of a significant amount of biologically active IGF-II protein. The IGF-II secreted by COLO 205 cells may stimulate cell growth in an autocrine fashion through the Type I IGF receptors.

Affinity Labels↗

PubMed2002

Commercial variants of the prothrombin time test as a screening test of acquired coagulation factor II, VII, and X deficiencies in dogs.

The aim of this study was to acquire the single factor sensitivity of three commercial variants of the prothrombin time test (PT(Va1)-Thrombotest, PT(Va2)-Normotest, PT(Va3)-Hepato Quick) for canine plasma. For this purpose, 38 samples from animals with coumarin intoxication followed by vitamin K(1) treatment who had a reduced activity of the coagulation factors II, VII, and/or X (experiment 1) as well as 25 plasma samples from animals with moderately reduced activity of the coagulation factors II, V, VII, and/or X caused by a hepatogenic synthesis disorder or disseminated intravascular coagulation (experiment 2), were examined. Measurements for all tests were performed according to the instructions of the manufacturer and also with higher plasma dilution. Furthermore, control measurements were performed with the conventional prothrombin time test (standard test; PT(ST)). The prothrombin time measured with the PT(Va3), which was prolonged in all samples from experiments 1 and 2, especially reflected with high sensitivity the reduced activity of the coagulation factors. The measurements with PT(Va2) and PT(Va1) showed only an insignificantly lower sensitivity (> or =0.88) with a maximum of 1 (experiment 1) and 3 (experiment 2) false negative test results, respectively. Compared to the already high sensitivity, a higher dilution of the sample material did not lead to a significantly higher sensitivity (P>0.05) for any of the tested commercial variants of the prothrombin time assay. While there was no significant difference (P>0.05) between the number of false negative test results in the variants of the prothrombin time assay, in both experiments a significantly higher number of false negative test results was found for the PT(ST) (P<0.001). The results show that, in contrast to the PT(ST), all three tested commercial prothrombin time variants are suitable for the detection of deficiencies of coagulation factors II, VII, and X in canine plasma.

Animals↗

PubMed1999

Dual role for transcription factor AP-2 in the regulation of the major fetal promoter P3 of the gene for human insulin-like growth factor II.

The human insulin-like growth factor II (IGF-II) gene contains four promoters that are differentially active during cell growth and development. Promoter 3 (P3) is the most active promoter in fetal and non-hepatic adult tissues. In addition to its expression during development, P3 is also the major promoter in many tumour tissues and IGF-II-expressing cell lines. Here we show that AP-2 has a dual function in P3 regulation in vivo as well as in vitro. In cells expressing low levels of endogenous AP-2, AP-2 overexpression activates P3, whereas P3 promoter activity is inhibited in cells containing abundant AP-2. Four potential AP-2-binding sites were identified in footprinting studies with recombinant AP-2. One of these AP-2-binding sites is located within the previously identified element P3-4 that contains two adjacent binding sites for IGF-II promoter-binding proteins IPBP3 and IPBP4/5. By applying binding competition assays and mutational analysis it is shown that AP-2 interferes with IPBP3 binding and transactivation in vivo as well as in vitro. Furthermore, AP-2 can bind additional elements in the proximal P3 promoter that also contribute to AP-2-mediated transactivation as shown by transient transfection assays. From these results we conclude that AP-2 is an important regulator in vivo and in vitro of IGF-II P3 activity.

Base Sequence↗

PubMed2001

Binding of anticoagulation factor II from the venom of Agkistrodon acutus with activated coagulation factor X.

Anticoagulation factor II (ACF II) from the venom of Agkistrodon acutus has been identified as a binding protein to activated bovine coagulation factor X (FXa) by the method of polyacrylamide gel electrophoresis and high performance liquid chromatography. This protein formed a 1:1 complex with FXa in the presence of Ca2+ ions, and the maximal binding of ACF II to FXa occurred at the concentration of Ca2+ ions of about 1mM. The binding of Ca2+ ions to ACF II was analyzed by equilibrium dialysis and two Ca2+-binding sites with different affinities were identified. At pH 8.0, the apparent association constant K1 and K2 values for these sites were (1.1+/-0.3)x10(5) M(-1) and (1.7+/-0.4)x10(4) M(-1) (mean+/-SE, n=4), respectively. It was evident from the observation of Ca2+-induced changes in the intrinsic fluorescence of ACF II that ACF II underwent a conformational change upon binding of Ca2+ ions. The occupation of both Ca2+-binding sites in ACF II requires a concentration of Ca2+ ions of about 1mM, which is equal to the effective concentration of Ca2+ ions required for maximal binding of ACF II to FXa, and for the maximal Ca2+-induced enhancement of emission fluorescence of ACF II. It can be deduced from these results that the occupation of both Ca2+-binding sites in ACF II with Ca2+ ions and subsequent conformational rearrangement should be essential for its recognition of Ca2+-mediated conformational changes of FXa.

Agkistrodon↗

PubMed1999

Recurrent optic nerve head infarctions associated with combined factor V Leiden- and factor II:G20210A-mutation.

PURPOSE: To demonstrate the association of bilateral recurrent optic nerve head infarctions with thrombophilia due to combined factor V:R506Q- and factor II:G20210A-mutation. METHODS: Case report. We examined a 55-year-old man with a two-year history of three segmental optic nerve head infarctions. Visual acuity was 20/80 on the left and 20/25 on the right eye. RESULTS: Ophthalmologic, cardiologic, radiologic, neurologic and hematologic-immunologic examinations were unremarkable except for increased APC-resistance (APC ratio: 1.4; normal value >2) due to heterozygous factor V:R506Q-mutation and high factor II-levels due to factor II:G20210A-mutation. Therapy with coumarin was instituted at INR 2.0-3.0 and no relapse has occurred over the past 1-year period. CONCLUSION: Combined occurrence of thrombogenic factor II:G20210A-mutation and factor V:R506Q-mutation may be causally linked to recurrent optic nerve head infarctions.

Factor V↗

PubMed1991

The chick embryo fibroblast cation-independent mannose 6-phosphate receptor is functional and immunologically related to the mammalian insulin-like growth factor-II (IGF-II)/man 6-P receptor but does not bind IGF-II.

The insulin-like growth factor-II (IGF-II)/Mannose 6-P receptor (Man 6-P) is a multifunctional receptor that binds two unrelated ligands, IGF-II and lysosomal enzymes that contain Man 6-P recognition markers. Although this receptor has been extensively characterized in mammalian cells, binding of radiolabeled IGF-II to this receptor in avian cells and tissues has not been reported. In the present study, we demonstrate that chick embryo fibroblasts (CEFs) bind and internalize lysosomal enzymes in a Man 6-P-inhibitable fashion, and possess a protein immunologically related to the mammalian IGF-II/Man 6-P receptor that binds lysosomal enzymes with Man 6-P recognition markers but does not bind IGF-II. 1) When lysates of biosynthetically labeled CEFs were affinity-purified on beta-galactosidase-Sepharose, an approximately 250 kilodalton protein was observed in the Man 6-P eluate but not in the Glc 1-P or mannose eluates, that was precipitated by antisera to purified rat and bovine IGF-II/Man 6-P receptors, but not by nonimmune serum. 2) When CEFs were incubated with [35S]proteins enriched in lysosomal enzymes, Man 6-P inhibited binding (0 C) and uptake (34 C) in a dose-dependent fashion. Binding was unchanged in the absence of divalent cations. At low sugar concentrations, binding and uptake were inhibited selectively by Man 6-P and the conformationally similar sugar phosphate, Fru 1-P, a specificity similar to that of mammalian cation-independent Man 6-P receptors. 3) When affinity-purified lysates from biosynthetically labeled CEFs were incubated with antiserum to the rat IGF-II/Man 6-P receptor, a 245 kilodalton protein was immunoprecipitated from lysates that had been affinity purified on beta-galactosidase-Sepharose but not after purification on IGF-II-Sepharose. By contrast, a truncated IGF-II/Man 6-P receptor, presumably internalized from the fetal bovine serum used to feed the cells, was purified from lysates of unlabeled CEFs on IGF-II-Sepharose. Thus, CEFs possess a cation-independent Man 6-P receptor that is similar in size and immunological reactivity to the mammalian IGF-II/Man 6-P receptor, and binds and internalizes lysosomal enzymes but, unlike the mammalian receptor, does not bind IGF-II.

Animals↗

PubMed1996

Nucleotide sequence and genomic structure of the chicken insulin-like growth factor-II (IGF-II) coding region.

Insulin-like growth factor II (IGF-II) is a mitogenic polypeptide with structural similarity to insulin that appears to be involved in regulating embryonic growth. While mammalian IGF-II proteins and IGF-II genes have been well characterized, little is known about avian IGF-II proteins and the genomic sequences that encode them. In this paper we report the isolation and characterization of chicken IGF-II cDNA and genomic clones. The predicted chicken prepro-IGF-II protein contains 187 residues and comprises a signal peptide (24 residues), IGF-II peptide (67 residues), and C-terminal peptide (96 residues), which share 33, 82, and 25/28% amino acid sequence identity, respectively, with their rat/human counterparts. Like the human and rat IGF-II genes, the chicken IGF-II gene has three coding exons. These are interrupted by introns at similar positions to those found in the human and rat IGF-II genes.

Amino Acid Sequence↗

PubMed1991

Identification of antisense transcripts of the chicken insulin-like growth factor-II gene.

Insulin-like growth factor-II (IGF-II) is a polypeptide mitogen which is believed to play an important role in fetal development. The human and rat IGF-II genes are complex transcription units, which contain multiple promoters and polyadenylation sites and which exhibit alternate splicing of their primary transcripts. In order to study IGF-II gene expression during chick embryonic development, we screened a 10-day chick embryo cDNA library with a human IGF-II cDNA probe. We isolated a clone, designated cigf, that was comprised, in part, of sequences homologous to the second coding exon of the human, mouse and rat IGF-II genes. Comparison of the nucleotide sequence of cigf with that of the corresponding genomic clone indicated that cigf was derived from a spliced antisense transcript of the chicken IGF-II gene, which overlapped the second coding exon. Northern blotting experiments with single-stranded RNA probes synthesized using cigf DNA as a template showed that stage 22 and stage 36 chick embryos contained sense strand IGF-II transcripts of 1.4, 2.2, 4.7 and 7.0 kb and antisense strand transcripts of 0.7, 1.3, 1.8, 2.5, 4.9, 6.0 and 8.0 kb. The pattern of sense strand IGF-II transcripts was similar to that previously found in rat fetal tissues. Whilst there are precedents for the transcription of both strands of a single gene, this is the first evidence for antisense transcription of an IGF gene. The functions of the antisense transcripts remain to be determined. These findings demonstrate a further level of complexity in the IGF-II transcription unit and indicate that studies of IGF-II transcript distribution performed with double-stranded probes should be interpreted with caution. They also suggest explanations for the recent finding that IGF-II peptides are present at much lower levels in embryos than expected from the high levels of IGF-II transcripts present.

Animals↗