Comparison of the nucleic acid sequence of anglerfish and mammalian insulin mRNA's from cloned cDNA's

The discovery of glucagon-like peptide 1

The discovery of glucagon-like peptide 1 (GLP-1) began more than two decades ago with the observations that anglerfish islet proglucagon messenger RNAs (mRNAs) contained coding sequences for two glucagon-related peptides arranged in tandem. Subsequent analyses revealed that mammalian proglucagon mRNAs encoded a precursor containing the sequence of pancreatic glucagon, intestinal glicentin and two glucagon-related peptides termed GLP-1 and GLP-2. Multidisciplinary approaches were then required to define the structure of biologically active GLP-1 7-36 amide and its role as an incretin, satiety hormone and, most recently, a neuroprotective peptide. This historial perspective outlines the use of traditional recombinant DNA approaches to derive the GLP-1 sequence and highlights the challenges and combination of clinical and basic science approaches required to define the physiology and pathophysiology of bioactive peptides discovered through genomics.

Evolution of the insulin molecule: insights into structure-activity and phylogenetic relationships

The conformation of insulin in the crystalline state has been known for more than 30 years but there remains uncertainty regarding the biologically active conformation and the structural features that constitute the receptor-binding domain. The primary structure of insulin has been determined for at least 100 vertebrate species. In addition to the invariant cysteines, only ten amino acids (GlyA1, IleA2, ValA3, TyrA19, LeuB6, GlyB8, LeuB11, ValB12, GlyB23 and PheB24) have been fully conserved during vertebrate evolution. This observation supports the hypothesis derived from alanine-scanning mutagenesis studies that five of these invariant residues (IleA2, ValA3, TyrA19, GlyB23, and Phe24) interact directly with the receptor and five additional conserved residues (LeuB6, GlyB8, LeuB11, GluB13 and PheB25) are important in maintaining the receptor-binding conformation. With the exception of the hagfish, only conservative substitutions are found at B13 (Glu --> Asp) and B25(Phe --> Tyr). In contrast, amino acid residues that were also considered to be important in receptor binding based upon the crystal structure of insulin (GluA4, GlnA5, AsnA21, TyrB16, TyrB26) have been much less well conserved and are probably not components of the receptor-binding domain. The hypothesis that LeuA13 and LeuB17 form part of a second receptor-binding site in the insulin molecule finds some support in terms of their conservation during vertebrate evolution, although the site is probably absent in some hystricomorph insulins. In general, the amino acid sequences of insulins are not useful in cladistic analyses especially when evolutionary distant taxa are compared but, among related species in a particular order or family, the presence of unusual structural features in the insulin molecule may permit a meaningful phylogenetic inference. For example, analysis of insulin sequences supports monophyletic status for Dipnoi, Elasmobranchii, Holocephali and Petromyzontiformes.

Elephantfish proinsulin possesses a monobasic processing site

Total pancreatic RNA from the holocephalan species Callorhyncus milii (elephantfish) was used to make cDNA as a template for the polymerase chain reaction. Three redundant primers based on the known amino acid sequence of elephantfish insulin were used to amplify a fragment of proinsulin comprising truncated B-chain, complete C-peptide, and complete A-chain. Whereas the C-peptide/A-chain junction contained the expected dibasic cleavage site (-Lys-Arg-), the B-chain/C-peptide junction was found to contain only a single Arg, the first such site to be unequivocally associated with the proteolytic processing of a proinsulin to insulin. Examination of the flanking sequences around this site shows that a typical endocrine/neuroendocrine PC3 conversion enzyme should still be able to cleave, as the general requirements for precursor processing at a monobasic site are satisfied, notably a basic residue (Lys) at the -4 position. An acidic residue (in this case Asp) at the +1 position, which is seen in all known proinsulins, is maintained. The corresponding genomic DNA fragment of elephantfish proinsulin was also amplified by PCR, revealing a 402-bp intron at the conserved IVS-2 position within the C7 codon.

Making (anti)sense of non-coding sequence conservation

A substantial fraction of vertebrate mRNAs contain long conserved blocks in their untranslated regions as well as long blocks without silent changes in their protein coding regions. These conserved blocks are largely comprised of unique sequence within the genome, leaving us with an important puzzle regarding their function. A large body of experimental data shows that these regions are associated with regulation of mRNA stability. Combining this information with the rapidly accumulating data on endogenous antisense transcripts, we propose that the conserved sequences form long perfect duplexes with antisense transcripts. The formation of such duplexes may be essential for recognition by post-transcriptional regulatory systems. The conservation may then be explained by selection against the dominant negative effect of allelic divergence.

Sequence-independent detection of gene family homologs: identification of a transcript encoding a molluscan serine protease homologous to the pancreatic enzymes of vertebrates

Autoradiography of 32P-labeled cDNA, fractionated at high resolution by electrophoresis through thin (0.8-1.5 mm) vertical alkaline agarose gels, provides a sequence-independent screening procedure for gene family homologs. A screen of tissues of a marine mollusc revealed a prominent intestine-specific cDNA encoding a pancreatic serine protease homolog, which was not detectable as a discrete poly(A)+ RNA species on formaldehyde agarose gels. Discrete cDNA products are authentic, non-truncated transcripts of tissue-specific mRNA. A band-sharpening effect is imparted to cDNA products due to (a) substitution of a uniform length 5'-oligo(dT) terminus for heterogeneous 3'-poly(A) termini and (b) the inherent superior resolution of alkaline-denatured DNA.

Identification of a second insulin-like growth factor in a fish species

An internal portion of insulin-like growth factor (IGF) amplified from the total cDNA of rainbow trout (Oncorhynchus mykiss) liver by a PCR was used to screen a rainbow trout liver cDNA library, and recombinant clones encoding two distinct IGFs were isolated. On the basis of a 98.7% nucleotide and 98.3% predicted amino acid identity to coho salmon IGF-I, one cDNA sequence was identified as rainbow trout preproinsulin-like growth factor I (rtIGF-I). The second cDNA sequence shared 46.1% and 43.3% identity with rtIGF-I at the nucleotide and predicted amino acid levels, respectively, and was identified as rainbow trout preproinsulin-like growth factor II (rtIGF-II). Predicted amino acid sequence comparisons of rtIGFs with those of human IGFs indicate that rtIGF-I is more similar to human IGF-I than to human IGF-II, and that rtIGF-II is more similar to human IGF-II than to human IGF-I. Southern blot analysis of rainbow trout genomic DNA probed with rtIGF-I and -II cDNA suggests that these two forms of IGF originate from separate genes. The presence of a teleost IGF-II suggests that the divergence of IGFs occurred early in vertebrate evolution.

Primary structure and tissue distribution of anglerfish carboxypeptidase H

Most peptide hormones are synthesized as part of larger precursor proteins which must be processed after translation to generate bioactive peptides. This usually involves cleavage of the precursor by an endopeptidase at sites marked by basic amino acids, followed by removal of N- or C-terminal basic residues by the action of an aminopeptidase or carboxypeptidase. These processing events have been observed in a variety of species, from yeast to mammals. As part of an effort to characterize prohormone processing enzymes in the anglerfish, Lophius americanus, we have cloned and sequenced a cDNA for the fish prohormone processing carboxypeptidase H (CPH). Polyadenylated RNA from anglerfish (AF) islet organs was used to construct a cDNA library in phage lambda gt11. The library was screened with a probe derived from the cDNA for rat CPH. A 2400 base pair AF cDNA clone was isolated. This cDNA encodes a polypeptide which is similar in size and composition to mammalian CPH. The sequence data indicate that the AF CPH precursor is a 454 amino acid polypeptide. The derived amino acid sequence of the putative fish CPH is 81% homologous to the rat and bovine CPH enzymes. Significantly, all of the amino acid residues thought to be important for metal ion and substrate binding, glycosylation, and catalytic activity of mammalian CPH are conserved in the fish enzyme. Northern hybridization using RNA from AF tissues indicates that a 2.5 kb fish CPH mRNA is expressed in brain, pituitary and islet organs, but not in other tissues which do not secrete peptide hormones.

Pancreatic endocrine cells in sea bass (Dicentrarchus labrax L.) II. Immunocytochemical study of insulin and somatostatin peptides

Insulin (INS)- and somatostatin (SST)-immunoreactive cells were demonstrated by light immunocytochemistry in the endocrine pancreas of sea bass (Dicentrarchus labrax). INS-immunoreactive cells were identified using bovine/porcine, bonito, and salmon (s) INS antisera; the immunostaining was abolished when each antiserum was preabsorbed with its respective peptide but not with unrelated peptides. These cells also reacted with mammal (m) SST-28 (4-14) antiserum. The immunoreaction did not change when this antiserum was preabsorbed by bovine INS. INS-immunoreactive cells were located in the central part of the endocrine areas of the principal, intermediate, and small islets. Two SST-immunoreactive cell types (D1 and D2) were revealed. D1 cells, immunoreactive to SST 14 (562) and sSST-25 antisera, were located next to the glucagon-immunoreactive cells in the peripheral part of the endocrine areas. D2 cells, immunoreactive to SST-14 (562), SST-14 (566), and mSST-28 (4-14) antisera, were found in apposition to the INS-immunoreactive cells. The specificity controls showed that D1 cells expressed sSST-25-like peptides, while D2 cells might contain SST-14 and/or mSST-28-like peptides. The close topographic association between the different SST-immunoreactive cells and both glucagon- and insulin-immunoreactive cells might indicate the existence of a specific paracrine regulation of each endocrine cell type in the sea bass endocrine pancreas.

Insulin gene expression in chicken ontogeny: pancreatic, extrapancreatic, and prepancreatic

Insulin has metabolic, growth, and differentiation effects in chicken embryos in vivo and it is required for normal development. Whether the pancreas is the sole source of insulin in embryogenesis is controversial. In the present study we investigated (1) the developmental pattern of expression of the chicken insulin gene in the pancreas; (2) the expression of the insulin gene in three nonpancreatic tissues, liver, brain, and lower limb, during chicken development; and (3) the expression of the insulin gene at prepancreatic stages and during chicken embryo organogenesis. Hybridization of synthetic species-specific insulin oligonucleotides to pancreatic frozen section in situ and to Northern blots revealed a major increase in insulin messenger RNA (mRNA) levels during the third week of embryonic development. The hybridization histochemistry showed both an increase in the levels of insulin mRNA per pancreatic islet and, in addition, an increase in the number of insulin mRNA containing islets with development. By Northern analysis there was a major polyadenylated transcript of 0.6 kb, which increased in abundance approximately 30-fold during this interval. Under the same stringency conditions used for pancreatic RNA an insulin transcript was detected in liver RNA blots. The abundance of this hepatic insulin mRNA was about 100-fold less than the pancreatic insulin mRNA and, in contrast to the latter, did not increase in late development. Primer extension experiments demonstrated that the insulin transcripts of pancreas and liver had similar 5' ends. No insulin mRNA was detected by Northern analysis or primer extension either in whole brain or lower limb total RNA from several developmental stages. A very low abundance insulin mRNA was detected in whole embryo at Day 8 and body regions at Day 4 and Day 5 when organogenesis of the pancreas takes place. Interestingly, a polyadenylated insulin transcript was detected, as well, in whole Day 2 and Day 3 embryos (stages 10 to 20, with 20 to 40 somites) before differentiation of beta cells occurs. Thus, there is differential developmental regulation of the insulin gene in several chicken embryo tissues and the expression of insulin precedes pancreatic maturation. These findings support the proposed role of insulin in differentiation and development in vivo and suggest a paracrine type of action of the hormone in early embryos before blood circulation begins.

Isolation and primary structure of the C-peptide of proinsulin from the European eel (Anguilla anguilla)

1. The primary structure of the C-peptide of proinsulin from the European eel has been established as: DVEPLLGFLSPKSGQENEVDDFPYKGQGEL. The peptide was isolated from the extract of eel pancreas in a yield that was approximately equimolar with insulin. A comparison with the predicted structures of C-peptides from other teleost fishes has identified a domain in the central region of the peptide that has been more highly conserved than the rest of the molecule.

Computer analysis suggests a role for signal sequences in processing polyproteins of enveloped RNA viruses and as a mechanism of viral fusion

We have used a computer program to scan the entire sequence of viral polyproteins for eucaryotic signal sequences. The method is based on that of von Heijne (1). The program calculates a score for each residue in a polyprotein. The score indicates the resemblance of each residue to that at the cleavage site of a typical N-terminal eucaryotic signal sequence. The program correctly predicts the known N-terminal signal sequence cleavage sites of several cellular and viral proteins. The analysis demonstrates that the polyproteins of enveloped RNA viruses--including the alphaviruses, flaviviruses, and bunyaviruses--contain several internal signal-sequence-like regions. The predicted cleavage site in these internal sequences are often known cleavage sites for processing of the polyprotein and are amongst the highest scoring residues with this algorithm. These results indicate a role for the cellular enzyme signal peptidase in the processing of several viral polyproteins. Not all high-scoring residues are sites of cleavage, suggesting a difference between N-terminal and internal signal sequences. This may reflect the secondary structure of the latter. Signal sequences were also found at the N-termini of the fusion proteins of the paramyxoviruses and the retroviruses. This suggests a mechanism of viral fusion analogous to that by which proteins are translocated through the membranes of the endoplasmic reticulum at synthesis.

Growth-controlling molluscan neurons produce the precursor of an insulin-related peptide

Insulin and related peptides are key hormonal integrators of growth and metabolism in vertebrates. There is little biochemical evidence for insulin-related peptides in invertebrates, apart from insects for which definitive structural information on these peptides (prothoracicotropic hormone, PTTH) has recently been obtained. We report here the first complete complementary DNA-derived primary structure of a preproinsulin-related protein from identified neurons in an invertebrate, the mollusc Lymnaea stagnalis. We have demonstrated by in situ hybridization that transcription of the gene for this molluscan insulin-related peptide (MIP) occurs in the cerebral light-green cells, giant neuroendocrine cells involved in the control of growth, as well as in a pair of neuroendocrine cells called the canopy cells. The insulin-related peptide precursor has the same overall structure as its vertebrate counterparts. The discovery of insulin-related peptides in invertebrates substantiates the evidence for a widespread and early evolutionary origin of the insulin superfamily.

Role in translation of a triple tandemly repeated sequence in the 5'-untranslated region of human thymidylate synthase mRNA

A triple tandem repeat (TTR) consisting of 90 nucleotides exists immediately upstream of the ATG initiator codon in human thymidylate synthase (TS) cDNA (pcHTS-1). To investigate the role of the TTR in the expression of the TS cDNA, we used pcHTS-1 to construct mutant cDNA clones in which part of the TTR was deleted or an additional element was inserted. The mutant cDNA plasmid was introduced into murine TS-negative mutant cells and the relative translation efficiencies of the mutant cDNAs were determined by measuring the transient expression of TS activity and the amount of TS mRNA transcribed. The translation efficiency in transient expression of the mutants was increased by deletions covering all the first two repeated elements, and the part of the third closest to the ATG initiator codon, but was not affected by deletions of only parts of the first two repeated elements at the 5' end. The translation efficiency was also not affected by insertion of an additional repeated element into the TTR. These results suggest that the first two repeated elements at the 5' end both have inhibitory effects on translation of the TS mRNA, probably due to the unique structural feature of this element.

Characterization of the two nonallelic genes encoding mouse preproinsulin

We have cloned and sequenced the two mouse preproinsulin genes. The deduced amino acid sequences of the mature mouse insulins are identical to the published protein sequences. However, the nucleotide sequence indicates that the mouse I C-peptide has a deletion of two amino acids compared with the mouse II C-peptide. We used an S1 nuclease assay to confirm the presence of the deletion and to measure the ratio of transcripts from gene I to transcripts from gene II. The mouse preproinsulin I gene, like the rat gene I, is missing the second intervening sequence that normally interrupts the C-peptide region in other insulin genes. Comparison of the 5' flanking sequences of the mouse and rat genes II indicates that they are homologous for at least 1000 base pairs. The preproinsulin I genes also share homology in their 5' flanking DNAs; however, their homology to the preproinsulin II genes extends for only about 500 base pairs.

The NH2 terminus of preproinsulin directs the translocation and glycosylation of a bacterial cytoplasmic protein by mammalian microsomal membranes

To investigate putative sorting domains in precursors to polypeptide hormones, we have constructed fusion proteins between the amino terminus of preproinsulin (ppI) and the bacterial cytoplasmic enzyme chloramphenicol acetyltransferase (CAT). Our aim is to identify sequences in ppI, other than the signal peptide, that are necessary to mediate the intracellular sorting and secretion of the bacterial enzyme. Here we describe the in vitro translation of mRNAs encoding two chimeric molecules containing 71 and 38 residues, respectively, of the ppI NH2 terminus fused to the complete CAT sequence. The ppI signal peptide and 14 residues of the B-chain were sufficient to direct the translocation and segregation of CAT into microsomal membrane vesicles. Furthermore, the CAT enzyme underwent N-linked glycosylation, presumably at a single cryptic site, with an efficiency that was comparable to that of native glycoproteins synthesized in vitro. Partial amino-terminal sequencing demonstrated that the downstream sequences in the fusion proteins did not alter the specificity of signal peptidase, hence cleavage of the ppI signal peptide occurred at precisely the same site as in the native precursor. This is in contrast to results found in prokaryotic systems. These data demonstrate that the first 38 residues of ppI encode all the information necessary for binding to the endoplasmic reticulum membrane, translocation, and proteolytic (signal sequence) processing.

Primary structure of insulin and a truncated C-peptide from an elasmobranchian fish, Torpedo marmorata

Insulin has been isolated from the pancreas of Torpedo marmorata, an elasmobranchian fish, and shown to contain 21 amino acid residues in the A-chain and 30 residues in the B-chain. The sequence of insulin has been strongly conserved within the class Elasmobranchii with only one substitution and one deletion in the A chain and one substitution in the B-chain compared with insulin from the spiny dogfish, Squalus acanthias. A second peptide, present in the pancreatic extracts in approximately equimolar concentration with insulin, was identified as a heptadecapeptide. The sequence of this peptide shows homology to the N-terminal region of anglerfish (Lophius americanus) C-peptide at six of 17 sites. The isolation of a truncated C-peptide suggests either that the sequence encoding the COOH-terminal region of T. marmorata C-peptide has been deleted from the preproinsulin gene or that a larger C-peptide has undergone a proteolytic cleavage in the central portion of the molecule during packaging in the secretory granules of the B cell.

Angiotensinogen gene is expressed and differentially regulated in multiple tissues of the rat

To define the role of local synthesis of angiotensinogen in tissue angiotensin production, we have quantitated angiotensinogen messenger RNA (mRNA) levels in 17 different tissues of four groups of rats: control rats, nephrectomized rats, rats given dexamethasone, ethynylestradiol, and triiodothyronine, and nephrectomized rats given dexamethasone, ethynylestradiol, and triiodothyronine. Angiotensinogen mRNA was identified in 12 tissues: liver, kidney, brain, spinal cord, aorta, mesentery, atria, lung, adrenal, large intestine, stomach, and spleen. Angiotensinogen mRNA was not identified in pituitary, ventricle, testis, small intestine, or pancreas. When expressed per gram tissue wet weight, angiotensinogen mRNA levels of extrahepatic tissues were less than 4% of hepatic levels. However, when expressed per milligram total RNA, angiotensinogen mRNA levels of brain, spinal cord, aorta, and mesentery were 26-42% of hepatic levels. Regulation of angiotensinogen mRNA levels was tissue specific. This demonstration of a widespread tissue distribution of angiotensinogen mRNA may indicate a similarly widespread distribution of local angiotensin systems that are independent of the circulating renin-angiotensin system.

Biosynthesis and processing of the somatostatin family of peptide hormones

Understanding of the biosynthesis of the somatostatin family of peptide hormones has greatly increased in recent years. Isolation and sequencing of the rat somatostatin gene indicates that it contains a single intron located between the codons for Gn(-57) and Glu(-56) of pre-prosomatostatin. The gene contains three repetitive sequences, one at the 5' end of the gene and two of them 3' to the coding portion. Two of the sequences consist of alternating purine-pyrimidine bases and have been shown to adopt Z-DNA structures in vitro. The cDNA for rat somatostatin codes for a 116-residue peptide structurally similar to the anglerfish and catfish precursors to the 14-residue somatostatin (SST-14). In addition to SST-14, the catfish and the anglerfish both contain an additional pancreatic somatostatin, each derived from a different gene. The catfish contains a 22-residue somatostatin, which is O-glycosylated at Thr-5. The second somatostatin gene from anglerfish encodes a prosomatostatin that is processed to a 28-residue peptide. The mature peptide contains a hydroxylated lysine at position 23.

Homology requirements for recombination in Escherichia coli

The DNA sequence homology required for recombination in Escherichia coli has been determined by measuring the recombination frequency between insulin DNA in a miniplasmid pi VX and a homologous sequence in a bacteriophage lambda vector. A minimum of approximately equal to 20 base pairs in a completely homologous segment is required for significant recombination. There is an exponential increase in the frequency of recombination when the length of homologous DNA is increased from 20 base pairs to 74 base pairs and an apparently linear increase with longer DNA segments. Mismatches within a homologous segment can dramatically decrease the frequency of recombination. Thus, the process of recombination is sensitive to the length of precisely base-paired segments between recombining homologues.

Characterization of coho salmon (Oncorhynchus kisutch) insulin

Insulin has been isolated from islet tissue of coho salmon (Oncorhynchus kisutch) by gel filtration and HPLC and the complete amino acid sequence has been determined. The sequence differs from bovine insulin at 14 sites but all interchanges are conservative from the viewpoint of preservation of conformation. A comparison of insulin sequences from other fish is presented. Salmon insulin cross-reacts very weakly with antiserum to bovine insulin and vice versa. A completely homologous radioimmunoassay has been developed and used to estimate the insulin in salmon islet tissue and in plasma. The hypoglycemic effect of salmon insulin in salmon was more pronounced and persisted longer than that caused by identical doses of bovine insulin.

Presence of hormonogenic and repetitive domains in the first 930 amino acids of bovine thyroglobulin as deduced from the cDNA sequence

The sequence of the first 2831 nucleotides of bovine thyroglobulin mRNA has been determined from the analysis of a cDNA clone. Following a 41-nucleotide 5' untranslated sequence, a single open-reading frame encoding 930 amino acids was observed. This corresponds to the aminoterminal third of thyroglobulin, preceded by a putative signal peptide of 19 amino acids. The protein sequence was found to be essentially made of the sevenfold repetition of a 60-amino-acid-long building unit, interrupted at fixed positions by unrelated segments of variable length. The presence of an internal homology within the repetitive unit itself suggests that the 5' region of the thyroglobulin gene has evolved from the initial duplication of a relatively short sequence, followed by the serial duplication of the resulting unit. The tyrosine residue at position five has been assigned an important hormonogenic function [Mercken, L., Simons, M.-J. and Vassart, G. (1982) FEBS Lett. 149, 285-287]. This residue is flanked by sequence elements related to the repeated unit, suggesting that the hormonogenic domain evolved also from the basic ancestor sequence.

Regulation of hormone biosynthesis in cultured islet cells from anglerfish

The effects of glucose and arginine on islet hormone biosynthesis were investigated using primary cell cultures prepared from islets of the anglerfish (Lophius americanus). After dispersion under sterile conditions, islet cells were maintained at 23 degrees C in medium containing RPMI 1640 with Hanks' buffer, pH 7.5, modified by the adjustment of glucose (to 0.56 or 5.6 mM) and arginine (to 0.1, 1.15, or 10 mM) with the addition of 10% fetal bovine serum (dialyzed, heat inactivated) and penicillin/streptomycin. After 48 h, media were replaced by incorporation media containing [14C]isoleucine and [3H]tryptophan and incubated for an additional 8 h under otherwise identical conditions. Culture samples (cells plus media) were extracted, desalted, and gel filtered to identify and quantitate [14C]insulin, [3H]glucagon(s) plus [3H]somatostatin-28, and [3H]somatostatin-14. In some experiments, [14C]insulin, [3H]glucagon(s), [3H]somatostatin-28, and [3H]somatostatin-14 were separated by high performance liquid chromatography. Raising the medium glucose from 0.56 (control) to 5.6 mM resulted in an augmentation in incorporation of [14C]isoleucine into insulin and an augmentation of [3H]tryptophan into glucagon(s) and somatostatin-14, but no change in incorporation of [3H]tryptophan into somatostatin-28. Raising the concentration of arginine from 0.1 to 1.15 or 10 mM resulted in a dose-dependent inhibition of labeled amino acid incorporation into all hormones except somatostatin-28. The results demonstrate the usefulness of the culture system for studying the modulation of hormone biosynthesis in anglerfish islet cells.

Effect of insulin on meiosis reinitiation induced in vitro by three progestogens in oocytes of the goldfish (Carassius auratus)

Three progestogens were tested for their ability to elicit meiosis reinitiation as evidenced by germinal vesicle dissolution (GVD) in goldfish (Carassius auratus) follicle-enclosed oocytes in vitro. In two independent experiments 17 alpha-20 beta-dihydroxyprogesterone (DHP) was most active followed in turn by 17 alpha-hydroxyprogesterone (HP) and progesterone (P). Values of the effective dose for a 50% response for GVD induced by P and HP were significantly reduced by the addition of Na-insulin, however, insulin had no significant effect on DHP incubates. Meiotogenic activity was potentiated by Na-insulin in the following heirarchy: P greater than HP greater than DHP. These results indicate that insulin, which had little meiotogenic activity alone, was capable of differentially enhancing progestogen activity in this system. The mechanism by which Na-insulin augments progestogen GVD-inducing activity is unknown, but may include decrease of progestogen degradation, increase in progestogen biosynthesis, and direct insulin effects on the oocyte. The results suggest that insulin may play a physiological role in goldfish oocyte meiosis reinitiation by enhancing the activity of certain progestogens, which by themselves are not potent meiotogens.

Association of newly synthesized islet prohormones with intracellular membranes

Results from recent studies have indicated that pancreatic islet prohormone converting enzymes are membrane-associated in islet microsomes and secretory granules. This observation, along with the demonstration that proglucagon is topologically segregated to the periphery within alpha cell secretory granules in several species, led us to investigate the possibility that newly synthesized islet prohormones might be associated with intracellular membranes. Anglerfish islets were incubated with [3H]tryptophan and [14C]isoleucine for 3 h, then fractionated by differential and density gradient centrifugation. Microsome (M) and secretory granule (SG) fractions were halved, sedimented, and resuspended in the presence or absence of dissociative reagents. After membrane lysis by repeated freezing and thawing, the membranous and soluble components were separated by centrifugation. Extracts of supernatants and pellets were chromatographed by gel filtration; fractions were collected and counted. A high proportion (77-79%) of the newly synthesized proinsulin and insulin was associated with both M and SG membranes. Most of the newly synthesized proglucagons and prosomatostatins (12,000-mol-wt precursors) were also membrane-associated (86-88%) in M and SG. In contrast, glucagon- and somatostatin-related peptides exhibited much less membrane-association in SG (24-31%). Bacitracin, bovine serum albumin EDTA, RNAse, alpha-methylmannoside, N-acetylglucosamine, and dithiodipyridine had no effect on prohormone association with membranes. However, high salt (1 M KCl) significantly reduced membrane-association of prohormones. Binding of labeled prohormones to SG membranes from unlabeled tissue increased with incubation time and was inhibited by unlabeled prohormones. The pH optimum for prohormone binding to both M and SG membranes was 5.2. It is suggested that association of newly synthesized prohormones with intracellular membranes could be related to the facilitation of proteolytic processing of prohormones and/or transport from their site of synthesis to the secretory granules.

Guinea pig preproinsulin gene: an evolutionary compromise?

We characterized a clone carrying the guinea pig preproinsulin gene, which, in contrast to other mammalian preproinsulin genes, is highly divergent in its regions encoding the B and A chains of mature insulin. Blot hybridization analysis indicates that this gene is present in only one copy in the guinea pig genome and that other normal or mutated preproinsulin genes do not exist in this animal. Moreover, the position of introns in this gene and the homology of its 3' flanking region to the corresponding regions of other sequenced mammalian genes show that it has been derived from the common mammalian stock. The rapid evolution of the region encoding the B and A chains can be interpreted, according to our sequence-divergence analysis, as due to the fixation of both neutral and adaptive mutations.

Complete sequence of one of the mRNAs coding for the small subunit of ribulose bisphosphate carboxylase of Nicotiana sylvestris

The combination of cDNA and RNA sequencing techniques has enabled determination of the complete sequence of one of the mRNAs coding for the precursor of the small subunit of ribulose bisphosphate carboxylase of Nicotiana sylvestris. In this 898-nucleotide-long mRNA, 540 nucleotides code for the entire 180-amino-acid-long precursor polypeptide consisting of the 57-amino acid-long transit peptide and the 123-amino-acid-long mature protein, while 60 and 195 nucleotides belong to the 5' and 3' noncoding flanking regions, respectively. The 5' end, which is very rich in AG residues, contains several direct and indirect repeated sequences, and a possible hairpin structure. The 3' end, terminated by a 103-nucleotide-long poly-A tail, is very rich in AU residues but does not contain the classical polyadenylation signal sequence.

Compilation and analysis of sequences upstream from the translational start site in eukaryotic mRNAs

5-Noncoding sequences have been tabulated for 211 messenger RNAs from higher eukaryotic cells. The 5'-proximal AUG triplet serves as the initiator codon in 95% of the mRNAs examined. The most conspicuous conserved feature is the presence of a purine (most often A) three nucleotides upstream from the AUG initiator codon; only 6 of the mRNAs in the survey have a pyrimidine in that position. There is a predominance of C in positions -1, -2, -4 and -5, just upstream from the initiator codon. The sequence CCAGCCAUG (G) thus emerges as a consensus sequence for eukaryotic initiation sites. The extent to which the ribosome binding site in a given mRNA matches the -1 to -5 consensus sequence varies: more than half of the mRNAs in the tabulation have 3 or 4 nucleotides in common with the CCACC consensus, but only ten mRNAs conform perfectly.

Carp preproinsulin cDNA sequence and evolution of insulin genes

The nucleic acid sequence of the preproinsulin cDNA of carp (Cyprinus carpio), cloned in the PstI-site of pBR322 (1), has been determined. The sequenced insert of 439 bp includes the complete coding information for carp preproinsulin (108 amino acids), 10 nucleotides of the 5'-and 105 nucleotides of the 3'-nontranslated regions. The nucleotide sequence confirms the previously established amino acid sequence of carp insulin (2) and determines those of the signal (21 aa 1) and C-peptide (35 aa 1). The observed shortness of the signal peptide of carp preproinsulin and the N-terminal addition of 2 amino acids to the carp insulin B-chain suggest that the cleavage site of the signal peptidase has moved. Calculations based on the comparison of known preproinsulin cDNA sequences showed that the evolutionary distance between fresh water and salt water teleostians is not smaller than between man and chicken.

Patterns of amino acids near signal-sequence cleavage sites

According to the signal hypothesis, a signal sequence, once having initiated export of a growing protein chain across the rough endoplasmic reticulum, is cleaved from the mature protein at a specific site. It has long been known that some part of the cleavage specificity resides in the last residue of the signal sequence, which invariably is one with a small, uncharged side-chain, but no further specific patterns of amino acids near the point of cleavage have been discovered so far. In this paper, some such patterns, based on a sample of 78 eukaryotic signal sequences, are presented and discussed, and a first attempt at formulating rules for the prediction of cleavage sites is made.

Statistical characterization of nucleic acid sequence functional domains

It has long been recognized that various genome classes were distinguishable on the basis of base composition and nearest neighbor frequencies. In addition Grantham et al. (8) have recently presented evidence that these distinctions are preserved at the level of codon usage. As discussed in this report it is now clear that these and related statistics can uniquely characterize the various functional domains of the genome. In particular peptide coding, intervening segments, structural RNA coding and mitochondrial domains of the vertebrate genome are uniquely characterizable. The statistical measures not only reflect understood functional differences among these domains but suggest others. The ability of these simple statistics of nucleic acid sequences to reflect so much of the encoded complex pattern information and/or effects of selective constraints is somewhat surprising. Here, we investigated the statistical measures most distinctive of the various domains and then linked them to our current understandings in so far as possible.

Nucleotide sequence analysis of the cloned salmon preproinsulin cDNA

A cDNA library was constructed using polyadenylated RNA from salmon (Oncorhynchus keta) Brockmann bodies, plasmid vector pBR322, and in vitro recombinant DNA techniques. Insulin-related clones were identified with a cDNA probe generated from the same RNA and enriched for insulin sequences. Two recombinants were shown to contain the nucleotide sequence of the entire coding region and parts of the 5' and 3' untranslated regions. The salmon preproinsulin mRNA is about 760 nucleotides long, 315 of which code for the protein, while about 190 and 200 nucleotides belong to the 5' and 3' flanking regions, respectively. Comparison of the nucleotide sequences of salmon insulin mRNA with those from other species reveals that sequence conservation is limited to the regions coding for the B and A peptides and two segments of the signal peptide. The C-peptide region exhibits no significant sequence homology with the C-peptides of other vertebrates. The 5' and 3' untranslated regions of the salmon preproinsulin mRNA are homologous only with the anglerfish mRNA, whereas there is no evident homology with those of birds and mammals. In addition to establishing the sequence of the preproinsulin mRNA, cloned salmon insulin cDNA provides a specific probe for the analysis and isolation of genomic DNA fragments containing insulin genes.

Sequence of a cDNA encoding pancreatic preprosomatostatin-22

We report the nucleotide sequence of a precursor to somatostatin that upon proteolytic processing may give rise to a hormone of 22 amino acids. The nucleotide sequence of a cDNA from the channel catfish (Ictalurus punctatus) encodes a precursor to somatostatin that is 105 amino acids (Mr, 11,500). The cDNA coding for somatostatin-22 consists of 36 nucleotides in the 5' untranslated region, 315 nucleotides that code for the precursor to somatostatin-22, 269 nucleotides at the 3' untranslated region, and a variable length of poly(A). The putative preprohormone contains a sequence of hydrophobic amino acids at the amino terminus that has the properties of a "signal" peptide. A connecting sequence of approximately 57 amino acids is followed by a single Arg-Arg sequence, which immediately precedes the hormone. Somatostatin-22 is homologous to somatostatin-14 in 7 of the 14 amino acids, including the Phe-Trp-Lys sequence. Hybridization selection of mRNA, followed by its translation in a wheat germ cell-free system, resulted in the synthesis of a single polypeptide having a molecular weight of approximately 10,000 as estimated on Na-DodSO4/polyacrylamide gels.

The nucleotide sequence of cDNA coding for preproinsulin from the primate Macaca fascicularis

DNA complementary to preproinsulin messenger RNA from the primate Macaca fascicularis has been cloned into the PstI endonuclease site of the plasmid pBR322. One clone contains the entire preproinsulin coding region as well as 59 nucleotides of the 5'-untranslated region. The results predict an amino acid sequence for the Macaca fascicularis preproinsulin and establish for the first time that the primary structures of human and primate insulins are identical. The two amino acid exchanges between human and primate preproinsulins are restricted to the pre- and the C-peptide, respectively.

Immunological characterization of catfish (Ictalurus punctatus) insulin and proinsulin

1. Insulin and insulin intermediates were isolated and characterized from catfish (Ictalurus punctatus) pancreatic islets. 2. An antibody developed to this catfish insulin allowed the identification of proinsulin, and insulin intermediates. 3. Amino acid composition of the isolated insulin intermediates was similar to the calculated amino acid composition of proinsulin, as determined from the analyses of the separate A, B and C chains.

Characterization of proinsulin- and proglucagon-converting activities in isolated islet secretory granules

The conversion of proglucagon and proinsulin by secretory granules isolated from both prelabeled and unlabeled anglerfish islets was investigated. Either granules isolated from tissue labeled with [3H]tryptophan and [14C]isoleucine or [35S]cysteine, or lysed granules from unlabeled tissue to which exogenously labeled prohormones had been added were incubated under various conditions. Acetic acid extracts of these granule preparations were analyzed for prohormone and hormone content by gel filtration. Both prelabeled and lysed, unlabeled secretory granules converted radiolabeled precursor peptides (Mr 8,000-15,000) to labeled insulin and glucagon. The accuracy of the cleavage process was established by demonstrating comigration of products obtained from in vitro cleavage with insulin and glucagon extracted from intact islets using electrophoresis and high-pressure liquid chromatography (HPLC). The pH optimum for granule-mediated conversion was found to be in the range of pH 4.5-5.5. Conversion of both proglucagon and proinsulin by secretory granules was significantly inhibited in the presence of antipain, leupeptin, p-chloromercuribenzoate (PCMB) or dithiodipyridine (DDP) but not chloroquine, diisopropyl fluorophosphate, EDTA, p-nitrophenyl guanidinobenzoate, soybean trypsin inhibitor, or N-p-tosyl-L-lysine chloromethyl ketone HCl. The inhibitory action of PCMB and DDP was reversed in the presence of dithiothreitol. Both membranous and soluble components of the secretory granules possessed significant converting activity. HPLC and electrophoretic analysis of cleavage products demonstrated that the converting activities of the membranous and soluble components were indistinguishable. The amount of inhibition of proinsulin and proglucagon conversion caused by 600 micrograms/ml porcine proinsulin was significantly lower than that caused by the same concentration of unlabeled anglerfish precursor peptides. These results indicate that the proinsulin and proglucagon converting enzyme(s) in the anglerfish pancreatic islet is a unique intracellular thiol proteinase(s) that may be granule membrane-associated and may require the presence of prohormone sequences in addition to the dibasic residues at cleavage sites for substrate recognition and/or binding.