Reproductive isolation between sympatric Anguilla japonica and Anguilla marmorata

Species-specific restriction fragment length polymorphism in the intron of the androgen receptor gene (ar5) was found in glass to silver-stage individuals of Anguilla japonica (n = 51) and A. marmorata (n = 21). The sequence analysis of 16S rDNA from 328 anguillid leptocephali collected in the North Equatorial Current of the western North Pacific Ocean revealed the specimens to be A. japonica (n = 194), A. marmorata (n = 128), A. bicolor pacifica (n = 5) and A. luzonensis (n = 1). All leptocephali of A. japonica and A. marmorata were monomorphic and did not share an allele at the ar5 locus, indicating that the two species are reproductively isolated.

A giant anguilliform leptocephalus Thalassenchelys foliaceus Castle & Raju is a junior synonym of Congriscus maldivensis (Norman 1939)

A single specimen of giant leptocephalus Thalassenchelys foliaceus Castle & Raju 1975 was caught in subtropical waters of the western North Pacific Ocean. Mitochondrial coI gene sequence divergence between T. foliaceus and Congriscus maldivensis (Norman 1939) was 0·64 ± 0·27% (mean ± s.e.), and the myomere and vertebral counts of these species were similar, indicating T. foliaceus is a junior synonym of C. maldivensis.

Remarkably low mtDNA control-region diversity and shallow population structure in Pacific cod Gadus macrocephalus

To investigate the genetic diversity and describe the population structure in Gadus macrocephalus, a 452 base pair (bp) fragment of the mitochondrial DNA control region was analysed in 259 individuals. The results showed remarkably low nucleotide diversity and a lack of genealogical structure. Small but significant genetic differentiations, however, were detected among north-western Pacific populations, but no large-scale regional differences were detected. These results indicate that populations of G. macrocephalus in the north-western Pacific are genetically subdivided and represent evolutionary lineages that should be managed individually.

Population genetic structure and larval dispersal potential of spottedtail goby Synechogobius ommaturus in the north-west Pacific

Larval dispersal may have an important effect on genetic structure of benthic fishes. To examine the population genetic structure of spottedtail goby Synechogobius ommaturus, a 478 base pair (bp) fragment of the hypervariable portion of the mtDNA control region was sequenced and used to interpret life-history characteristics and larval dispersal strategy. Individuals (n = 186) from 10 locations on the coasts of China and Korea were analysed and 44 haplotypes were obtained. The levels of haplotype and nucleotide diversity were higher in East China Sea populations than in other populations. Both the phylogenetic tree and the minimum spanning tree showed that no significant genealogical structures corresponding to sampling locations existed. AMOVA and pair-wise F(ST) revealed significant genetic differentiation between populations from Korea and China. A significant isolation by distance pattern was observed in this species (r = 0.53, P < 0.001). Both mismatch distribution analysis and neutrality tests showed S. ommaturus to have experienced a recent population expansion. These results suggest that the Pleistocene ice ages had a major effect on the phylogeographic pattern of S. ommaturus, that larvae might avoid offshore dispersal and that dispersal of larvae may maintain a migration-drift equilibrium.

Mouse cytochrome P450 (Cyp3a11): predominant expression in liver and capacity to activate aflatoxin B1

S1 mapping analysis for the expression of Cyp3a11 and Cyp3a13 indicated that Cyp3a11 mRNA is predominantly expressed in mouse liver, compared with that of Cyp3a13. In addition, all of six inducers, such as dexamethasone, 3-methylcholanthrene, phenobarbital, polychlorinated biphenyl, pregnenolone 16 alpha-carbonitrile, and rifampicin, increased the expression of the Cyp3a11 mRNA more extensively than that of Cyp3a13. The level of mRNAs corresponding to Cyp3a11 and Cyp3a13 reached the maximum level between 4 and 8 weeks after birth. Cyp3a11 enzyme was expressed into CR119 cells which had been established as a cell line stably expressing NADPH-cytochrome P450 reductase cDNA of guinea pigs. These transformants showed aflatoxin B1-dependent cytotoxicity in proportion to the amounts of Cyp3a11 mRNA. This cytotoxicity was enhanced by 7,8-benzoflavone, a known activator of CYP3A protein. Based on these results, we confirm that CYP3A in the mouse, which is an animal species known to be relatively insensitive to aflatoxin B1 genotoxicity, can activate this mycotoxin efficiently.

Gene structure of mouse Cyp3a11: evidence for an enhancer element within its 5' flanking sequences

A mouse Cyp3a11 gene was isolated from a mouse sperm DNA library with mouse Cyp3a11 cDNA as a probe. The nucleotide sequences determined for the gene and the 5' flanking region revealed that the mouse Cyp3a11 gene was composed of 13 exons and 12 introns. The exons spun about 23 kb. The nucleotide sequence of the exons was completely identical to Cyp3a11 cDNA. Within the 5' flanking sequence, putative binding sites of several transcriptional factors were found. Transient transfection assays were carried out with HepG2 cells, a human hepatoma cell line, using constructs containing different lengths of 5' flanking sequence fused to a reporter, chloramphenicol acetyltransferase gene. The results showed that a cis-acting element(s) was located from -1609 to -907.

Molecular cloning and functional expression of a mouse cytochrome P-450 (Cyp3a-13): examination of Cyp3a-13 enzyme to activate aflatoxin B1 (AFB1)

A cDNA encoding a novel member of the cytochrome P-450 superfamily, Cyp3a-13, has been isolated from mouse liver cDNA library by hybridization screening. The Cyp3a-13 encoded 503 amino acid residues and shared 71% amino acid identity with Cyp3a-11. When Cyp3a-13 cDNA was expressed in CR119 cells which had been established as a cell line stably expressing NADPH-cytochrome P-450 reductase cDNA of guinea pigs, aflatoxin B1-dependent cytotoxicity was observed. This cytotoxicity was enhanced by alpha-naphthoflavone (7,8-benzoflavone), which is known to augment the CYP3A enzymatic activity. The results indicate that CYP3A in mice, which are relatively insensitive to aflatoxin B1, can activate aflatoxin B1 to a genotoxic product.

A novel form of mouse cytochrome P450 3A (Cyp3a-16). Its cDNA cloning and expression in fetal liver

A complementary DNA clone coding for a novel form of cytochrome P450, Cyp3a-16, in mouse fetal livers was isolated and completely sequenced. This clone encoded a polypeptide of 504 deduced amino acids and showed 87.3% and 66.6% amino acid identities with mouse Cyp3a-11 and Cyp3a-13, respectively. Cyp3a-16 transcript was detectable before birth and remarkably diminished five weeks after birth in mice. We conclude that Cyp3a-16 is a fetal- and puberty-specific cytochrome P450 in mice.

Statistical methods for the beta-binomial model in teratology

The beta-binomial model is widely used for analyzing teratological data involving littermates. Recent developments in statistical analyses of teratological data are briefly reviewed with emphasis on the model. For statistical inference of the parameters in the beta-binomial distribution, separation of the likelihood introduces an likelihood inference. This leads to reducing biases of estimators and also to improving accuracy of empirical significance levels of tests. Separate inference of the parameters can be conducted in a unified way.

Mouse liver cytochrome P-450 (P-450IIIAM1): its cDNA cloning and inducibility by dexamethasone

A full-length cDNA complementary to mouse liver mRNA coding for one of the cytochromes P-450 (P-450) in the P-450IIIA family, namely P-450IIIM1, was isolated and completely sequenced. The sequence of this cDNA clone, pMDex13, revealed that it encoded a polypeptide of 504 deduced amino acid residues (Mr = 57,853). The deduced amino acid sequence showed 87.3 and 84.9% identity with rat P-450IIIA1 and P-450IIIA2, respectively. The NH2-terminal 24 amino acid sequences of P-450IIIAM1 were completely identical with purified mouse P-450UT protein. RNA blot analysis showed that mRNA content of hepatic P-450IIIAM1 was remarkably increased by treatment of mice with dexamethasone.

Genomic organization of human fetal specific P-450IIIA7 (cytochrome P-450HFLa)-related gene(s) and interaction of transcriptional regulatory factor with its DNA element in the 5' flanking region

P-450IIIA7 is a form of cytochrome P-450 which was isolated from human fetal livers and termed P-450HFLa. This form has been clarified to be expressed during fetal life specifically (Komori, M., Nishio, K., Kitada, M., Shiramatsu, K., Muroya, K., Soma, M., Nagashima, K. and Kamataki, T. (1990) Biochemistry 29, 4430-4433). In the present study, we isolated five independent clones which probably corresponded to the human P-450IIIA7 gene. These clones were completely sequenced, all exons, exon-intron junctions and the 5' flanking region from the cap site to-869. Although the sequences in the coding region were completely identical to P-450IIIA7, it is possible that genomic fragments sequenced in this study encode portions of other P-450IIIA7-related genes since we could not obtain a complete overlapping set of genomic clones. Within its 5' flanking sequence, the putative binding sites of several transcriptional regulatory factors existed. Among them, it was shown that a basic transcription element binding factor (BTEB) actually interacted with the 5' flanking region of this gene.

Estimation of safe doses: critical review of the hockey stick regression method

The hockey stick regression method is a convenient method to estimate safe doses, which is a kind of regression method using segmented lines. The method seems intuitively to be useful, but needs the assumption of the existence of the positive threshold value. The validity of the assumption is considered to be difficult to be shown. The alternative methods which are not based on the assumption, are given under suitable dose-response curves by introducing a risk level. Here the method using the probit model is compared with the hockey stick regression method. Computational results suggest that the alternative method is preferable. Furthermore similar problems in the case that response is measured as a continuous value are also extended. Data exemplified are concerned with relations of SO2 to simple chronic bronchitis, relations of photochemical oxidants to eye discomfort and residual antibiotics in the lever of the chicks. These data was analyzed by the original authors under the assumption of the existence of the positive threshold values.