Expression of R- ras oncogenes in the hermaphroditic fish Kryptolebias marmoratus, exposed to endocrine disrupting chemicals

Abstract

The hermaphroditic fish Krytolebias marmoratus is a potential fish model for study of tumour development. Recently, sequences and expression of some oncogenes and tumor suppressor gene have been studied in K. marmoratus. To get a better understanding of oncogene expression at different development stage, and in different tissues three R- ras genes were cloned and fully sequenced. Expression of these R- ras genes (R- ras1, R- ras2, R- ras3) was also studied in fish exposed to endocrine-disrupting chemicals (EDCs). Liver showed the highest level of expression compared to other tissues, even though each R- ras gene showed different expression patterns in tissues. Interestingly, in secondary male (ovary atresia stage), expression levels of three R- ras genes was lower compared to hermaphrodites. At different developmental stages, R- ras2 gene showed most pronounced expression at early embryogenesis but at stage 5 (hatchling stage) and juvenile stage, R- ras3 gene showed the highest expression. After the juvenile stage, R- ras1 gene was upregulated compared to other R- ras genes, which showed the highest expression at the hermaphroditic stage. When fish were exposed to 17-β-estradiol (E2), a natural estrogen and tamoxifen, a nonsteroidal estrogen antagonist and three EDCs viz., 4-n-nonylphenol (NP), bisphenol A (BPA), and 4- tert-octylphenol (OP), all the three R- ras genes were induced, except in the fish exposed to tamoxifen. These results suggest that EDCs modulate the expression of R- ras genes and thus affect subsequent signal transduction and tumor development.