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Activated ras alleles have been detected in a wide range of human neoplasms, and c-N-ras mutations predominate in haematopoietic neoplasms. Ras oncogenes have been implicated in several animal and human models of multistep carcinogenesis. Malignant histiocytosis is a rare neoplasm of dogs that appears unique to the Bernese Mountain Dog. In the present study, we have examined the c-N-ras gene in two normal and 16 neoplastic Bernese Mountain Dog tissues by a polymerase chain reaction sequencing strategy. No activation of c-N-ras alleles was detected at codons 12, 13 or 61- those sites for ras proto-oncogene activations in human neoplasms. Indeed, in those regions of the first and second exons of canine c-N-ras examined, the nucleotide sequences derived from malignant histiocytosis specimens were identical to those derived from normal tissues, and the Bernese Mountain Dog sequence was identical to that which we have previously described in the Beagle dog. c-N-ras mutation does not appear to be associated with the aetiopathogenesis of malignant histiocytosis in the Bernese Mountain Dog.

Wild type equine p53 was amplified between exons 2 and 9 by the polymerase chain reaction using primers designed from conserved regions in other species. An 828 base pair region, corresponding to codons 25-313 of human p53, was sequenced in both directions. Human and equine amino acid sequences were 87% homologous in this region and 96% homologous in conserved domains II-V. Of eight equine cutaneous or mucocutaneous squamous cell carcinomas directly sequenced from exons 5-8, two had p53 point mutations resulting in single amino acid substitutions.

An 828 base pair region of canine wild-type p53, corresponding to codons 25 through 312 in the human p53 gene, was directly sequenced from asymmetric polymerase chain reaction (PCR) products. The deduced amino acid sequence of the dog was 86%, 73% and 83% homologous to that of the cat, mouse and human proteins, respectively. In the evolutionarily conserved domains II through V, the canine sequence approached 100% homology with the human sequence. The region sequenced encompasses exons 3-8 where the majority of mutations have been identified in neoplastic specimens from human patients.

Activated c-N- ras alleles have been detected in human lymphoma specimens. The aim of the present study was to determine the frequency of c-N- ras mutational activation in canine malignant lymphoma. DNA was isolated from 28 canine malignant lymphoma specimens collected from 28 separate dogs and examined for c-N- ras mutations by polymerase chain reaction amplification and direct sequencing. The tumors were naturally occurring and derived from 20 dogs with known exposures to the phenoxy herbicide 2,4-dichlo-rophenoxyacetic acid (2,4-D) and from 8 dogs with no known exposure to the herbicide. An oncogenically activating mutation was found in 1 dog without known 2,4-D exposure. The mutation was a 13th codon, second position transition that would result in a glycine-to-aspartate amino acid substitution. The results of this study demonstrate that, similar to the human, c-N- ras mutations are uncommon in dogs with malignant lymphoma and that there is no association between 2,4-D exposure and activation of c-N- ras in the dog.