Expressed sequence tags of medaka (Oryzias latipes) liver mRNA

A medaka liver cDNA library was constructed in lambda ZAPII. The number of clones in this library is approximately 5 x 10(6). Three hundred sixty-one clones were randomly selected and, of these, 33 clones with over 1 kb were sequenced. These sequences were compared with GenBank and the dbEST (Re.96.0). Twenty-five clones of these 33 clones encoded 18 different genes and 2 different expressed sequence tags (ESTs). Sequences of 10 of the 18 clones had not previously been reported in fish. The codon usage of medaka genes is similar to that of Xenopus, mouse, and human genes, but not similar to that of yeast and Escherichia coli genes.

Characterization and expression of c-type lysozyme cDNA from Japanese flounder (Paralichthys olivaceus)

Lysozyme is a widely distributed enzyme located in the serum, skin mucus, and other organs of fish, which is responsible for catalyzing the hydrolysis of the cell walls of most bacteria. A c-type of lysozyme cDNA was cloned from a kidney cDNA library of the Japanese flounder (Paralichthys olivaceus). The cDNAs consisted of 612 bp, which coded for 143 amino acid residues. The deduced amino acid sequence of Japanese flounder c-type lysozyme possessed 72.9%, 57.4%, and 65.4% identities with rainbow trout, chicken, and human c-type lysozymes, respectively. Comparison of the c-type lysozymes showed that the catalytic residues, the residues binding to sugar chains, and cysteine residues were completely conserved. Northern blot analysis indicated that the c-type lysozyme gene is apparently transcribed in the head kidney, posterior kidney, spleen, brain, and ovary of healthy flounder. When flounder were experimentally infected with Edwardsiella tarda, quantities of the c-type lysozyme mRNA increased in the head kidney, spleen, and ovary of the flounder.

Cloning and sequencing of cDNAs of the β-globin gene family in carp

A total blood cell cDNA library was constructed using a 3-year-old carp Cyprinus carpio. A β-globin cDNA (CβG1) was identified from the library by the polymerase chain reaction using a β-globin-specific primer deduced from the carp β-globin-A amino acid sequence. Also, five additional types of β-globin cDNAs (CβG2∼6) were isolated by colony hybridization using CβG1 as a probe. Sequence analysis revealed that these CβGs encoded 147 amino acids, and the deduced amino acid sequences showed high identity (89·1-95·2%) to previously reported carp β-globin amino acid sequences. The nucleotide sequences of the CβGs were very similar (identity 96·0-99·6%) and the expression levels of CβG1∼6 were 28·6, 28·6, 21·4, 14·3, 3·6 and 3·6% of the total number of cloned CβGs, respectively. Although the complete amino acid sequence identities between the CβGs and the β-globin of higher vertebrates were low, functionally important regions such as the α-βcontact region and haem contact region were well conserved. These data showed that, as in higher vertebrates, the adult carp has a multiple β-globin gene family (at least six members). However, transcripts encoding four types of peptides (CβG1 type, CβG2 and 3 type, CβG5 type, and CβG4 and 6 type) were expressed at relatively high levels, this being a unique character of the carp haemoglobin system.

Cloning and characterization of transferrin cDNA and rapid detection of transferrin gene polymorphism in rainbow trout (Oncorhynchus mykiss)

A cDNA clone of rainbow trout (Oncorhynchus mykiss) transferrin was obtained from a liver cDNA library. The 2537-bp cDNA sequence contained an open reading frame encoding 691 amino acids and the 5' and 3' noncoding regions. The amino acid sequences at the iron-binding sites and the two N-linked glycosylation sites, and the cysteine residues were consistent with known, conserved vertebrate transferrin cDNA sequences. Single N-linked glycosylation sites existed on the N- and C-lobe. The deduced amino acid sequence of the rainbow trout transferrin cDNA had 92.9% identities with transferrin of coho salmon (Oncorhynchus kisutch); 85%, Atlantic salmon (Salmo salar); 67.3%, medaka (Oryzias latipes); 61.3% Atlantic cod (Gadus morhua); and 59.7%, Japanese flounder (Paralichthys olivaceus). The long and accurate polymerase chain reaction (LA-PCR) was used to amplify approximately 6.5 kb of the transferrin gene from rainbow trout genomic DNA. Restriction fragment length polymorphisms (RFLPs) of the LA-PCR products revealed three digestion patterns in 22 samples.

Iron-regulated haemolysin gene from Edwardsiella tarda

We have cloned and sequenced the haemolysin gene locus from Edwardsiella tarda (ETH). This region encoded two open reading frames, designated ethA and ethB. ethA is the haemolysin gene consisting of 4782bp encoding a product of 165.3 kDa and ethB is an activation/secretion protein gene of 1677bp that encodes a product of 61.9 kDa. There were two putative ferric uptake regulator (Fur) binding sites on the 5' upstream region of the ethB gene overlapping the promoter region and ribosome-binding site. The haemolysin produced by the cloned gene was secreted by Escherichia coli. The deduced amino acid sequences of the ethA and ethB genes were found to be homologous to those of the haemolysin and activation/secretion proteins of Haemophilus ducreyi, Proteus mirabilis, and Serratia marcescens. E. coli carrying the ethA gene but not the ethB gene completely lost haemolytic activity, although the ethA gene was transcribed. The protein expressed by E. coli carrying a recombinant plasmid which encoded the ethA gene had haemagglutination activity. The EthB protein was necessary for activation of EthA protein (haemolysin). The ethA and ethB genes were very prevalent in haemolytic E. tarda strains isolated from diseased fish. Transcription of the ethB gene was regulated by iron. The ethA and ethB genes were transcribed independently.

Demonstration of ras and p53 gene mutations in carcinomas in the forestomach and intestine and soft tissue sarcomas induced by N-methyl-N-nitrosourea in the rat

The presence of ras family and p53 gene mutations in rat forestomach, intestine and liver tumors and soft tissue sarcomas induced by N-methyl-N-nitrosourea (MNU) was examined using polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) followed by direct sequencing analysis. In the forestomach squamous cell carcinomas (SCC), Ha-ras and p53 mutations were detected in 2 (40%) and 4 (80%) of 5 cases, respectively. The figures for Ki-ras and p53 gene mutations in adenocarcinomas of the large and small intestines were 3 (18.8%) and 5 (31.3%) of 16 cases. Soft tissue sarcomas in different sites were found to have mutations of Ki-ras in 7 (23.3%) and of p53 in 9 (30%) of 30 cases. One forestomach SCC and 2 soft tissue sarcomas had double p53 mutations in different exons. Single cases of forestomach SCC and intestinal adenocarcinoma had mutations in both Ki-ras and p53 genes. No mutations were found in counterpart benign tumors or hepatocellular adenomas. The p53 mutation spectrum revealed preferential clustering within exon 8 for the forestomach SCCs, and exons 5 and 8 for the intestinal adenocarcinomas, whereas the distribution was evenly spread through exons 5 to 8 in soft tissue sarcomas. All the detected ras or p53 mutations were G:C to A:T transitions. These results indicate firstly that specific Ki-ras, Ha-ras and p53 gene mutations in MNU-induced lesions are related to particular alkylation sites (G:C to A:T transitions) and secondly, although not essential, Ki-ras, Ha-ras or p53 gene mutations may be involved in the progression stage of forestomach, intestine and soft tissue neoplasms induced by MNU.

Cloning and detection of the hemolysin gene of Vibrio anguillarum

A 5 kb DNA fragment encoding a hemolysin was cloned from the fish pathogenic bacterium Vibrio anguillarum using the cosmid vector charomid9-36. An open reading frame of the hemolysin gene (VAH1) was 2253 bp and corresponded to a protein of 751 amino acid residues. The deduced amino acid sequence of the VAH1 gene and the previously reported Vibrio cholerae EI Tor hemolysin, V. vulnificus cytolysin-hemolysin, Aeromonas hydrophila AHH1 hemolysin, and A. salmonicida ASH4 hemolysin showed a significant degree of sequence homology, and the overall amino acid identities were 57.3%, 25.8%, 46.2%, and 43.7%, respectively. DNA hybridization analysis under high-stringent conditions using VAH1 as a probe, demonstrated that VAH1 hybridized with 25 out of 28 strains of V. anguillarum including serotypes A to I, but did not hybridize with other species of Vibrio, A. hydrophila or A. salmonicida. The targeted DNA fragment of VAH1 was successfully amplified from V. anguillarum-infected fish tissues by PCR.

Structure of medaka transferrin gene and its 5'-flanking region

Transferrin is a monomeric iron-binding glycoprotein. To investigate the structure of the transferrin gene in teleosts, we prepared a genomic DNA library from the medaka (Oryzias latipes). The medaka transferrin gene was isolated, and its nucleotide sequence was determined. The full length of this gene is approximately 8.5 kb, and it is organized into 17 exons separated by 16 introns. The exons are similar in size to those in the genes for human transferrin, chicken ovotransferrin, and mouse and bovine lactoferrin. However, the introns are smaller than those previously reported in the transferrin family of genes. The 5'-flanking region of the medaka transferrin gene contains an estrogen-responsive element, glucocorticoid-responsive elements, an iron-responsive element, metal-responsive elements, and Sp1 binding sites. The transcription start point is located 35 bp upstream of the start codon.

A highly repetitive sequence isolated from genomic DNA of the medaka (Oryzias latipes)

A highly repetitive interspersed DNA sequence (MRE) was isolated from the genome of medaka, Oryzias latipes, and characterized. Three distinct sequences of MRE were cloned and compared. The conserved sequences of MRE were approximately 220 bp in length. On average, one copy of MRE was present in every 153 kb, and the number of copies of MRE in the genome was calculated to be approximately 9800. MRE constituted approximately 0.14% of the genome. MRE-related sequences were not detected in carp (Cyprinus carpio) red-spot masu trout (Oncorhynchus masou macrostomus), masu salmon (Oncorhynchus masou masou), rainbow trout (Oncorhynchus mykiss), eel (Anguilla japonica), Arctic lamprey (Lampetera japonica), or yellowtail (Seriola quinqueradiata). MRE was randomly distributed in the medaka genome, indicating a high incidence of polymorphism in the five medaka inbred lines.

K-ras point mutations in cancerous and noncancerous biliary epithelium in patients with pancreaticobiliary maljunction

BACKGROUND

Pancreaticobiliary maljunction (PBM), an anomalous union of the pancreatic duct with the common bile duct, has frequently been shown to be associated with biliary carcinoma. However, the mechanism of carcinogenesis is unknown.

METHODS

Mutations of the K-ras oncogene were examined in cancerous and noncancerous biliary tract epithelium of 20 patients with PBM by an extraction of DNA from surgically resected histologic specimens. DNA was analyzed by a polymerase chain reaction single strand conformation polymorphism (PCR-SSCP) method and direct sequencing.

RESULTS

An abnormally mobilized DNA band was detected not only in cancerous epithelium but also in hyperplastic, metaplastic, and inflammatory epithelium of the gallbladder and/or common bile duct in patients with PBM. Among the biliary epithelium of patients with PBM, point mutation of K-ras oncogenes were detected in 4 of 5 (80%) cancerous epithelium, 7 of 12 (58%) hyperplastic and metaplastic epithelium, and 8 of 18 (44%) inflammatory epithelium, whereas no point mutation of the K-ras oncogene was detected in the gallbladder epithelium in 3 control patients without PBM. Direct sequence analysis of the K-ras oncogene revealed the mutation at codon 12 substituting the wild-type glycine (GGT) for aspartic acid (GAT) in all cancerous lesions of patients with PBM. Simultaneous two-point mutations from the wild-type glycine (GGC) to arginine (CGC) at codon 13 associated with the mutation at codon 12 were also found in one case of gallbladder carcinoma and one case of bile duct carcinoma.

CONCLUSIONS

K-ras gene mutation is involved in the carcinogenesis of biliary tract epithelium in patients with PBM, and appears to be a high risk factor for carcinogenesis of the biliary tract.

Isolation of major histocompatibility complex class I cDNA from pink salmon (Oncorhynchus gorbuscha)

An MHC class I cDNA clone was isolated from pink salmon (Oncorhynchus gorbuscha). Eight amino acids, which have been shown in mammals to bind main-chain atoms of peptides, are well conserved in the salmon alpha 1 and alpha 2 domains. Nine amino acids in the alpha 3 domain are classified by Williams and Barclay (Ref. 1. Ann. Rev. Immunol. 6:381-405, 1988) as signature immunoglobulin superfamily residues. The pink salmon MHC class I extracellular domains show 84.2% amino acid identity with those of Atlantic salmon (Sasa p30). polymorphism of the MHC class I alpha 1 domain was determined using PCR with genomic DNA from 12 fish. Sixteen variants were identified with most diversity concentrated in those amino acids that bind directly to peptides in mammalian class I molecules. Non-synonymous substitutions predominate over synonymous ones in the codons encoding these polymorphic residues.

K-ras point mutations in cancerous and noncancerous biliary epithelium in patients with pancreaticobiliary maljunction

BACKGROUND

Pancreaticobiliary maljunction (PBM), an anomalous union of the pancreatic duct with the common bile duct, has frequently been shown to be associated with biliary carcinoma. However, the mechanism of carcinogenesis is unknown.

METHODS

Mutations of the K-ras oncogene were examined in cancerous and noncancerous biliary tract epithelium of 20 patients with PBM by an extraction of DNA from surgically resected histologic specimens. DNA was analyzed by a polymerase chain reaction single strand conformation polymorphism (PCR-SSCP) method and direct sequencing.

RESULTS

An abnormally mobilized DNA band was detected not only in cancerous epithelium but also in hyperplastic, metaplastic, and inflammatory epithelium of the gallbladder and/or common bile duct in patients with PBM. Among the biliary epithelium of patients with PBM, point mutation of K-ras oncogenes were detected in 4 of 5 (80%) cancerous epithelium, 7 of 12 (58%) hyperplastic and metaplastic epithelium, and 8 of 18 (44%) inflammatory epithelium, whereas no point mutation of the K-ras oncogene was detected in the gallbladder epithelium in 3 control patients without PBM. Direct sequence analysis of the K-ras oncogene revealed the mutation at codon 12 substituting the wild-type glycine (GGT) for aspartic acid (GAT) in all cancerous lesions of patients with PBM. Simultaneous two-point mutations from the wild-type glycine (GGC) to arginine (CGC) at codon 13 associated with the mutation at codon 12 were also found in one case of gallbladder carcinoma and one case of bile duct carcinoma.

CONCLUSIONS

K-ras gene mutation is involved in the carcinogenesis of biliary tract epithelium in patients with PBM, and appears to be a high risk factor for carcinogenesis of the biliary tract.

Decreased levels of 2-amino-3-methylimidazo[4,5-f]quinoline-DNA adducts in rats treated with beta-carotene, alpha-tocopherol and freeze-dried aloe

To assess mechanisms of chemoprevention of hepatocarcinogenesis by trans-beta-carotene (beta-C), DL-alpha-tocopherol (alpha-T), and freeze-dried whole leaves of Kidachi aloe (Aloe), formation of 2-amino-3-methylimidazo[4,5-f]quinoline (IQ)-DNA adducts was measured by 32P-post-labeling analysis, and CYP1A1 and CYP1A2 protein levels were analyzed by ELISA. Group 1 rats were fed diet containing 0.02% beta-C, 1.5% alpha-T or 30% Aloe over an 8-day period, while group 2 was given basal diet alone. On day 7, all animals were subjected to two-thirds partial hepatectomy (PH). Twelve hours after PH, they received a single dose of the carcinogenic food pyrolysate IQ (100 mg/kg) intragastrically, to initiate hepatocarcinogenesis. Rats were killed 6, 12, 24 and 48 h after IQ administration. The levels of adducts, expressed as relative adduct labeling values in rats treated with beta-C, alpha-T and Aloe, were decreased as compared with the control group at hour 24 (36 h after PH), with a significant difference in the case of the beta-C group (46.4% of the control value). Similarly, all showed a tendency for decrease at hour 48. Furthermore, the levels of CYP1A2, known to be responsible for activation of IQ, showed a significant reduction at hour 24. It is concluded that beta-C, and possibly also alpha-T and Aloe, have the potential to reduce IQ-DNA adduct formation, presumably as a result of decreased formation of active metabolites. The results may explain, at least in part, the previously observed inhibitory effects of these compounds on induction of preneoplastic hepatocellular lesions.

Temperature acclimation induces light meromyosin isoforms with different primary structures in carp fast skeletal muscle

Carp acclimated to 10 degrees C gave 69k, 66k, and 62kDa light meromyosin (LMM) fragments in SDS-PAGE, while fish acclimated to 30 degrees C gave 74k, 69k, 66k, and 62kDa fragments. The microsequence analysis revealed that the 69k and 66kDa components from the 10 degrees C-acclimated carp contained an N-terminal amino acid sequence different from that of 62kDa. The four fragments from the 30 degrees C-acclimated carp showed the same sequence as that of the 69k and 66kDa components from the 10 degrees C-acclimated carp, except that the 2nd amino acid, Ala, of the 10 degrees C-acclimated LMM was replaced by Thr. DNA fragments encoding an N-terminal region of LMM were amplified by PCR or reverse transcriptase-PCR, demonstrating that the two acclimated groups further contained several amino acids substituted.

Genotoxic activity in vivo of the naturally occurring glucoside, cycasin, in the Drosophila wing spot test

Cycasin, methylazoxymethanol-beta-glucoside, is a naturally occurring carcinogenic compound. The genotoxicity of cycasin was assayed in the Drosophila wing spot test. Cycasin induced small single and large single spots on feeding at 10 mumol/g medium. The presence of these spots indicates that cycasin is genotoxic in Drosophila melanogaster. Microorganisms which showed beta-glucosidase activity for cleaving cycasin to toxic aglycon were isolated from gut flora of the Drosophila larvae. Consequently, the Drosophila wing spot test would be useful for mutagenicity screening of other naturally occurring glucosides.

Chemopreventive effects of beta-carotene, alpha-tocopherol and five naturally occurring antioxidants on initiation of hepatocarcinogenesis by 2-amino-3-methylimidazo[4,5-f]quinoline in the rat

Inhibitory effects of naturally occurring antioxidants on the initiation stage of hepatocarcinogenesis were studied. Group 1 rats were given a diet containing beta-carotene (beta-CT, 0.02%), alpha-tocopherol (alpha-TP, 1.5%), glutathione (GLT, 5%), vanillin (VNL, 1%), quercetin (QCT, 1%) or ellagic acid (ELA, 1%), or 3 doses of diallyl sulfide (DAS, 200 mg/kg, i.g.) over an 8-day period. On day 7, the animals received a single dose of 2-amino-3-methylimidazo[4,5-f] quinoline (IQ, 100 mg/kg, i.g.), 12 h after two-thirds partial hepatectomy for initiation and 2 weeks thereafter, were placed on promotion regimen comprising phenobarbital (0.05% in diet) and a single dose of D-galactosamine (100 mg/kg, i.p.). Groups 2 and 3 were treated as described for Group 1, but without test material or IQ, respectively. Survivors were killed at week 11 and antioxidant influence was assessed by comparing values for preneoplastic glutathione S-transferase placental form-positive (GST-P+) foci between Groups 1 and 2. All lesions larger than 70 microns in diameter consisting of approximately 5 cells in cross section were counted. Numbers of GST-P+ foci/cm2 in Group 1 were: beta-CT, 7.99; alpha-TP, 8.21; GLT, 9.71; DAS, 10.37; VNL, 10.57; QCT, 11.1; ELA, 12.5 (n = 11-15). All, except ELA, showed a significant decrease as compared with the Group 2 value of 14.54 (n = 15). Only beta-CT showed a significant decrease for the area value. This is the first report to show that beta-CT, alpha-TP, GLT, DAS, VNL, QCT exert inhibitory effects on initiation of hepatocarcinogenesis by the food carcinogen IQ, suggesting that these antioxidants might find application as chemopreventive agents. Furthermore, the current protocol proved practical for the assessment of chemopreventive agents within 11 weeks, a relatively short period.

Reproduction of progressive retinal degeneration (bright blindness) in sheep by administration of ptaquiloside contained in bracken

The process of occurrence of bright blindness, progressive retinal degeneration (PRD), in sheep was observed using two Suffolk ram lambs fed on a diet containing bracken powder. The first sign of the bright blindness was detected 4 months after the start of experiment. Based on these preliminary results, the amount of bracken powder necessary to induce PRD was estimated (experiment I). In the following experiment, ptaquiloside (PT), a norsesquiterpene glucoside of the illudane type isolated from bracken, which is a bracken carcinogen and a causative principle of cattle bracken poisoning was administered to two Suffolk ram lambs. It was clearly demonstrated in this experiment (experiment II) that PT present in bracken is also a causative principle of PRD.

Cloning and characterization of three hemolysin genes from Aeromonas salmonicida

Two hemolysin genes (ASH3 and ASH4) of Aeromonas salmonicida strain 17-2 and one (ASH1) of A. salmonicida ATCC14174 were cloned into the cosmid vector charomid 9-36 in Escherichia coli DH1. The overall amino acid sequence of the ASH3 was similar to that of the aerolysins of Aeromonas hydrophila and Aeromonas sobria, and hemolysins AHH3, AHH4, and AHH5 of A. hydrophila, and hemolysin ASA1 of A. sobria. The sequence of ASH4 was similar to that of the AHH1 hemolysin of A. hydrophila. The ASH4 hemolysin contains some homologous sequence regions of the Vibrio vulnificus and Vibrio cholerae cytolysin-hemolysin. Both ASH3 and ASH4 DNA probes reacted with all 104 strains of A. salmonicida, whereas the ASH1 DNA probe did not hybridize with any of the 104 strains studied except strain ATCC14174. ASH1 and ASH3 were broad spectrum hemolysins with most activity against rabbit and horse erythrocytes, respectively, whereas ASH4 hemolysin did not lyse bovine and horse erythrocytes. ASH3 and ASH4, but not ASH1, were activated by trypsin.

Demonstration of initiation potential of carcinogens by induction of preneoplastic glutathione S-transferase P-form-positive liver cell foci: possible in vivo assay system for environmental carcinogens

In a development trial for an initiation bioassay system, 7 known carcinogens and 1 suspected carcinogen were examined. In experiment 1, group 1 animals were initially subjected to partial hepatectomy (PH) 12 h before administration of diethylnitrosamine, 2-amino-3-methylimidazo[4,5-f]-quinoline (IQ), captafol, alpha-hexachlorocyclohexane or diethylstilbestrol (DES), then 2 weeks later underwent a promotion procedure comprising administration of phenobarbital (0.05% in diet) for 8 weeks and D-galactosamine (300 mg/kg, i.g.) at week 3. Group 2 received the promotion protocol alone as in group 1. Initiating potential was assayed on the basis of significant increase in values of preneoplastic placental form glutathione S-transferase-positive (GST-P+) foci of more than 3 cells in cross section at week 10. Numbers and areas of GST-P+ foci in group 1 given IQ, captafol and DES were significantly increased as compared to group 2, confirming the validity of the protocol as an initiation assay. In Experiment 2, group 1 rats were subjected to PH and 12 h later received a suspected carcinogenic mixture of opium pyrolysate (OP) or carcinogenic pesticide p,p'-dichloro-diphenyltrichloroethane or hexachlorobenzene. Application of a modified promotion procedure comprising cholic acid (0.15%) and carbon tetrachloride (1 ml/kg, i.g.) revealed significant initiation potential for OP. Overall the results indicate that the current protocols may be useful for detection of the initiation potential of carcinogens irrespective of their mutagenicity.

Immunohistochemical localization of hepatocyte growth factor protein in pancreas islet A-cells of man and rats

Hepatocyte growth factor (HGF), a potent mitogen for adult rat hepatocytes in primary culture, has previously been shown to be primarily expressed in the nonparenchymal cells of the liver. Using polyclonal antisera against human and rat HGFs we studied the tissue distribution of HGF immunohistochemically and found the most intense staining in the pancreas islet cells in both man (autopsy cases) and the rat. Differential localization of 4 pancreas islet hormones, glucagon, insulin, somatostatin and pancreatic polypeptide, revealed HGF to be preferentially expressed within the glucagon‐positive cells. The results indicate that HGF is primarily produced or stored in A‐cells and may act as a growth factor in a paracrine and an endocrine fashion, like various other hormones.

Retinal degeneration induced by N-methyl-N-nitrosourea and detection of 7-methyldeoxyguanosine in the rat retina

Retinal degeneration induced by a single parenteral dose (40 mg) of N-methyl-N-nitrosourea (MNU) was studied in rats and rabbits. Sequential observations showed that severe pathological changes, that is, complete or widespread destruction of the photoreceptor layer and the outer nuclear layer of the retina, occurred in both animals by 72 hr after the administration of MNU. At week 5, at the end stage of the retinal degeneration induced by MNU, thin remnants remained with the inner nuclear layer in direct contact with the pigment epithelium. An additional immunohistochemistry study using antibodies against 7-methyldeoxyguanosine (7-mdGua), revealed the presence of high levels of 7-mdGua DNA adducts in the nuclei of the outer nuclear layer cells. This finding suggests that the alkylation of the outer nuclear layer by MNU was the direct cause of the retinal degeneration seen in these animals.

Nucleotide sequences and characterization of haemolysin genes from Aeromonas hydrophila and Aeromonas sobria

Extracellular haemolysin is thought to be one of the important virulence factors in Aeromonas infection. Two extracellular haemolysin genes (AHH3 and AHH4) from Aeromonas hydrophila strain 28SA, one (AHH5) from A. hydrophila strain AH-1 and one (ASA1) from Aeromonas sobria strain 33 were cloned into cosmid and plasmid vector DNA in Escherichia coli. The nucleotide sequences of the open reading frames of AHH3 and AHH4 are both 1476 basepairs (bp), whereas AHH5 and ASA1 are 1455 and 1467 bp in length, respectively. The deduced amino acid sequences of AHH3, AHH4, AHH5 and the previously reported aerolysin from A. hydrophila showed a significant degree of sequence homology of over 90% each. The amino acid identity of the ASA1 haemolysin and those from A. hydrophila and Aeromonas trota aerolysins ranged from 58-68%. From DNA hybridization analysis using our cloned haemolysin genes as probes, we found that the AHH5 and ASA1 DNA probes hybridized with about 31 and 75% strains of motile Aeromonas species, respectively. The activity of haemolysins of cloned genes were different in medium agar containing various erythrocytes.

Absence of ras family point mutations at codons 12, 13 and 61 in N-ethyl-N-hydroxyethylnitrosamine- or N-nitrosomorpholine-induced renal cell tumors in rats

The prevalence of Ki-ras, Ha-ras and N-ras point mutation within exons 1 and 2 was studied in 17 cases of renal cell tumors (8 carcinomas and 9 adenomas) induced by N-ethyl-N-hydroxyethyl-nitrosamine or N-nitrosomorpholine. DNA samples prepared from acetone-fixed, paraffin-embedded tissues were amplified by means of the polymerase chain reaction, and point mutations at codons 12, 13 and 61 were analyzed by direct sequence methods with oligonucleotide primers. No mutations were detected in any of the renal tumors. The results thus indicated that ras family point mutation is not necessary for kidney tumor development in rats, supporting the view that ras mutations may not be generally relevant to neoplastic development in various organs in different species.