HIGH FREQUENCY OF K-ras MUTATIONS IN PINK SALMON EMBRYOS EXPERIMENTALLY EXPOSED TO EXXON VALDEZ OIL

Abstract

Abstract-Previous studies demonstrated reduced survivorship of pink salmon embryos from populations in Prince William Sound, Alaska, USA, that were exposed to Exxon Valdez-released oil compared with populations from matched nonoiled streams. Survivorship was also significantly decreased in embyros from lineages that were oiled in Prince William Sound and reared in clean water under controlled hatchery conditions compared with the descendants of nonoiled lineages. This suggests that the effect of oiling on pink salmon populations was persistent and could be transmitted intergenerationally. However, the ability of environmentally released oil to cause DNA sequence alterations in natural populations has yet to be demonstrated. We used polymerase chain reaction analysis to screen for alterations in the K-ras oncogene in DNA from pink salmon embryos that were exposed under controlled laboratory conditions to weathered Prudhoe Bay crude oil. Polymerase chain reaction and direct DNA sequence analyses were used to identify mutational hotspots within exons 1 and 2 of K-ras, and 3Ј primer mismatch analysis was used to determine the frequency of mutations in the 40 offspring of two families of pink salmon that were experimentally exposed to oiled or clean gravel. Mutations were only observed at codons 12, 13, and 61 of K-ras, sites that are frequently mutated in animal and human tumors. All mutations resulted in deduced amino acid substitutions. As expected, in all individuals exhibiting mutations, the copy number of the normal allele exceeded that of the mutated allele. The frequencies of mutations in oiled embryos at K-ras exons 1 and 2 were 68 and 41%, respectively. K-ras mutations were not observed in siblings that were exposed to clean gravel or in the parents of the two experimental matings. These results indicate that exposure of pink salmon embryos to weathered Prudhoe Bay crude oil under controlled laboratory conditions can elicit somatic cell mutations in high frequency at mutational hotspots in genes such as K-ras. However, the frequency of these events in oiled natural populations of pink salmon and other vulnerable species in Prince William Sound and the heritability of these mutations within oiled lineages have yet to be evaluated.

Delayed effects on growth and marine survival of pink salmon Oncorhynchus gorbuscha after exposure to crude oil during embryonic development

“…More likely, it results from biochemical impairments acquired during early development. Roy et al (1999) described mutagenic effects of oil on pink salmon incubated under conditions similar to those described here. Consequently, reduced growth could conceivably result from damage to DNA which could impair gene regulation, divert energy to incipient carcinomas, or impair activity of enzymes responsible for modulating growth or foraging.…”

Chronic Exposure to Polynuclear Aromatic Hydrocarbons in Natal Habitats Leads to Decreased Equilibrium Size, Growth, and Stability of Pink Salmon Populations

“…Reported impairments to reproduction include reduced offspring survival rates , impaired reproductive behavior (Le Blanc et al 1997), and regulation (Van den Heuvel and Ellis 2002). Additional extinction risk may accrue from increased genetic load resulting from increased frequency of mutation (Roy et al 1999) or genetic damage to reproductive ability (White et al 1999).…”

Chronic Exposure to Polynuclear Aromatic Hydrocarbons in Natal Habitats Leads to Decreased Equilibrium Size, Growth and Stability of Pink Salmon Populations

“…Reported impairments to reproduction include reduced offspring survival rates (Bue et al 1996), impaired reproductive behavior (Le Blanc et al 1997), and regulation (Van den Heuvel and Ellis 2002). Additional extinction risk may accrue from increased genetic load resulting from increased frequency of mutation (Roy et al 1999) or genetic damage to reproductive ability (White et al 1999).…”