A COMPARISON OF CYTOCHROME P4501A (CYP1A) MESSENGER-RNA INDUCIBILITY IN 4 SPECIES OF ATLANTIC COAST ANADROMOUS FISHES

Quantification of levels of cytochrome P4501A (CYP1A) gene expression in sentinel species of fishes has been proposed as a management tool t o evaluate contamination of aquatic systems. Based on preliminary stud ies, we hypothesized that differences in CYP1A mRNA inducibility among individuals, populations, or species might lead to spurious conclusio ns when using this approach in environmental monitoring programs. To a ddress this possibility, we quantitated and compared CYP1A mRNA induct ion levels in four species of common Atlantic Coast estuarine fish: sm ooth flounder, hogchoker, striped bass, and Atlantic tomcod, which wer e treated with model chemicals (beta naphthoflavone (beta-NF), or benz o[a]pyrene at 10 ppm) known to induce CYP1A mRNA, or were exposed to c ontaminated environments. Species-specific CYP1A DNA probes were gener ated from PCR (polymerase chain reaction) amplification of genomic DNA using conserved oligonucleotide primers, and, along with cloned rainb ow trout and Atlantic tomcod CYP1A cDNA probes were used to quantify C YP1A mRNA levels in northern blot analyses. Successful PCR amplificati on of CYP1A hybridizable DNA fragments was observed for all four speci es. Results from northern blot analyses showed large differences in CY P1A mRNA induction among species; only Atlantic tomcod exhibited signi ficant induction of CYP1A mRNA for both chemically treated (97-fold) a nd environmentally exposed fish (34-fold). Significant, although lower , levels of induction were observed in beta-NF treated (14-fold) smoot h flounder, but not in environmentally exposed smooth flounder. Only l ow levels (not significant) of CYP1A gene induction were detected in h ogchokers and striped bass. We conclude that CYP1A mRNA inducibility d iffered significantly among fish taxa perhaps due to differences in re gulation of gene expression, suggesting that careful selection of sent inel species should be exercised prior to the use of CYP1A mRNA induct ion in environmental monitoring programs. However, the significance of differences in CYP1A mRNA inducibility in relation to higher level bi ological endpoints has yet to be determined.