Faculty Bibliography

Atlantic tomcod (Microgadus tomcod) from the cancer-prone Hudson River population exhibit a genetic polymorphism in the cytochrome P4501A (CYP1A) gene which is evidenced in Northern blot analyses by a truncated transcript and in Southern blot analyses by a deletion in the variant allele. To initially evaluate the functional significance of this polymorphism, we sought to characterize the molecular basis for this polymorphism and to determine its frequency in tomcod from other populations in which the prevalence of neoplasia is low. The common CYP1A allelic sequence was determined from beta-naphthoflavone-induced tomcod cDNA and from tomcod genomic DNA. A sequence of the variant CYP1A allele was obtained by direct sequence analysis of the amplicons of variant tomcod cDNA and genomic DNA. CYP1A exon and intron structure is highly conserved between tomcod and all other teleost and mammalian species compared. Similarity of the deduced tomcod, rainbow trout, and plaice amino acid sequences was 72%, whereas similarity between tomcod and mammalian sequences was approximately 50%. The variant tomcod CYP1A allele results from a 606-bp deletion in the 7th exon of the 3' untranslated region (UTR) of the cDNA. Polymerase chain reaction and Northern blot analyses revealed an absence of this CYP1A polymorphism in tomcod from other rivers. Studies in humans suggest that variation in CYP1A1 cDNA may impact on genetic susceptibility to environmentally induced neoplasia. Furthermore, studies in in vitro mammalian models indicate the importance of 3' UTRs on gene expression by impacting on the stability of transcript. These results suggest that the 3' UTR CYP1A polymorphism in tomcod may have consequences for the genetic susceptibility of Hudson River fish to hepatic neoplasia

Mark-recapture studies have shown that striped bass from the Hudson River and Chesapeake Bay migrate to the Bay of Fundy and its tributaries during spring and summer. The objective of this study was to determine the relative contributions of U.S. stocks and the endemic Shubenacadie River population to the adult striped bass aggregations that occurred during 1992 and 1993 in two rivers of the Bay of Fundy: the Saint John River, New Brunswick (where striped bass spawning may not presently occur), and the Shubenacadie River, Nova Scotia (where striped bass spawning occurs). Mitochondrial DNA genotype frequency data were used in a mixture model. Up to 97% of adults from the Saint John River were determined to be of U.S. origin, whereas less than 10% of adult striped bass collected in the Shubenacadie River were migrants from U.S. stocks. Consequently, we suggest that efforts to maintain or restore the Saint John River population with native broodstock may be unsuccessful owing to possible extinction of the native stock; however, protection of the Shubenacadie River spawning stock should be enhanced

Reverse transcriptase PCR (RT-PCR) was evaluated as an alternative to Northern blot analysis in quantifying levels of metallothionein (MT) mRNA. Killifish were exposed to water-borne cadmium (Cd) at concentrations ranging from 0 ppb to 46 ppb and their levels of hepatic MT mRNA were quantitated by both Northern blot analysis and RT-PCR. Both methods provided comparable results in that low constitutive levels of MT mRNA were observed in fish exposed to clean water, dose-responsiveness was seen in fish exposed to increasing concentrations of Cd, and sensitivities of both techniques were similar in detecting induced levels of MT mRNA in Cd exposed fish. These results suggest that RT-PCR may provide a sensitive and quantitative method to evaluate gene expression in fish from small, non-invasively sampled tissues

CYP1A gene expression has been implicated in the processing of environmental procarcinogens and levels of variation in CYP1A mRNA expression are high in both environmentally exposed and chemically treated Atlantic tomcod. The objective of this study was to evaluate the effects of physical and biological parameters such as temperature, sex, and reproductive state on within-group variation in CYP1A mRNA induction. Levels of variation in CYP1A mRNA expression were directly correlated with mean levels of gene induction. Our results indicate that sex and reproductive state, but not temperature, had significant effects on CYP1A mRNA inducibility in tomcod; however, these parameters did not account for all interindividual variation in CYP1A inducibility. Other intrinsic biological factors, such as genetic polymorphisms in molecular pathways leading to CYP1A induction, may contribute to the high levels of interindividual variation in CYP1A inducibility in Atlantic tomcod

We determined levels of hepatic cytochrome P4501A (CYP1A) mRNA, hepatic DNA adducts, and fluorescent aromatic compounds (FACs) in bile, a measure of exposure to polyaromatic hydrocarbons, in Atlantic tomcod from six river systems ranging from highly polluted to relatively pristine on the northeast North American coast (the Hudson River, New York; the St. Lawrence River, Quebec; the Miramichi River, New Brunswick; the Saco and Royal rivers, Maine; and the Margaree River, Nova Scotia). Hudson River tomcod showed the greatest response for all parameters, and tomcod from the Margaree River exhibited the least response. Tomcod from the Miramichi River exhibited marked induction of CYP1A mRNA but low levels of hepatic DNA adducts and biliary FACs, whereas fish from the St. Lawrence River showed no induction of CYP1A mRNA and moderately elevated levels of DNA adducts and biliary FACs. In tomcod from the Hudson and Miramichi rivers, the levels of CYP1A mRNA were 28 times and 14 times, respectively, as great as the levels in fish from the St. Lawrence, Saco/Royal, and Margaree rivers. Mean levels of DNA adducts varied from 120 nmol adducts/mol bases in Hudson River tomcod to < 3 nmol adducts/mol bases in fish from the Miramichi and Margaree rivers. Concentrations of FACs in the bile of tomcod from the Hudson and St. Lawrence rivers were 8 and 1.8 times, respectively, as great as the concentrations in tomcod from the Miramichi River and Margaree River. In tomcod from the Hudson River, all three biomarkers were markedly elevated; in the St. Lawrence River two biomarkers were elevated, in the Miramichi River one was elevated, but no biomarker was substantially elevated in fish from the Saco/Royal and Margaree rivers. Elevated levels of hepatic DNA adducts and biliary FACs in tomcod from the Hudson River suggest increased exposure to PAHs, consistent with previous studies

Many problems in fisheries science require markers to discriminate among individuals, populations, or species and to monitor representatives of these groupings through time. The nucleotide sequences of DNA typically offer more than 3 billion potentially informative markers-many orders of magnitude more than alternative approaches. Molecular techniques, once tedious, have advanced so that rapidly analyzing the numerous samples typically required to resolve fisheries problems is now possible. To date, most molecular analyses in fisheries science have focused on analysis of mitochondrial DNA (mtDNA), but newer approaches involving nuclear DNA (nDNA) show great promise. In particular, noncoding single copy nDNA may be more informative than mtDNA analyses for anadromous and marine species, in which low genetic diversity is frequently encountered. In this paper, we outline 12 categories of fisheries problems amenable to molecular approaches and provide a review of the structure and analysis of DNA, the nature of DNA variation in fishes, and the modes of analysis most suitable for particular questions. The future should witness the routine implementation of these techniques; such efforts would be enhanced by increased communication between managers and researchers, centralization of facilities, and standardization of nomenclature

Management options for the Delaware River population of striped bass Morone saxatilis depend on whether or not the population forms a discrete stock. The recent increase in striped bass in the Delaware River follows decades of scarcity and concern about the possible extinction of the original population. The increase may have resulted from one or more of the following: expansion of a remnant population, repopulation by migrants from the Chesapeake Bay, or repopulation by migrants from the Hudson River. To determine the origin of the present Delaware River striped bass population, we analyzed mitochondrial DNA (mtDNA) from 191 striped bass collected in the Delaware River between 1990 and 1992. Our results indicate the Delaware River striped bass population is genetically intermediate between the Chesapeake Bay and Hudson River populations; mtDNA major-length genotype frequencies of the Delaware River sample were significantly different (P < 0.05) from those of the Hudson River stock, whereas mtDNA minor-length genotype frequencies of the Delaware River sample differed significantly from those of the Chesapeake Bay stock (P < 0.005). This intermediacy, together with information from historical surveys that suggest the original population did not become extinct, favors the hypothesis that the present Delaware River striped bass stock represents expansion from the original Delaware River stock