Abstract
<p>Damselfish neurofibromatosis (DNF) is a transmissible cancer that affects bicolor damselfish (Pomacentrus partitus) on South Florida reefs, and is characterized by the formation of malignant neurofibromas, neurofibrosarcomas, and chromatophoromas. We have identified a potentially infectious agent in P. partitus which appears to be associated with the presence of DNF. This agent has been termed DNFX. The prevalence and copy number per cell of DNFX DNA were determined in healthy fish (HFs), tumored fish (TFs), and fish with experimentally induced tumors (EFs). Damselfish were collected on reefs having a high (>14% of adults affected) or low (<0.3% of adults affected) prevalence of DNF. HFs were significantly less likely to test positive for DNFX than TFs or EFs. HFs were also found to have a lower copy number (always <1 copy of DNFX per 25 cells) than TF tumors (average of 3 copies per cell) or organs (average of 1 copy per cell). EFs were more similar to TFs than to HFs, with a mean of 1 copy of DNFX per cell in tumors, and 1 copy of DNFX per 10 cells in grossly healthy organs. From high prevalence reefs, 100% of HFs tested positive for DNFX, which was significantly higher than the 60% of HFs that tested positive on low prevalence reefs. On the reefs, copy numbers in HFs were similar regardless of DNF prevalence rate. No juvenile fish tested were found to be positive for DNFX from either high or low prevalence sites. When the distribution of DNFX in individual grossly healthy organs was examined, a greater number of healthy TF organs were DNFX positive as the fish developed more tumors. In addition, there appeared to be little variation in DNFX sequence among cell lines, HFs, EFs, or TFs from South Florida. Formalin fixed museum specimens were also analyzed for the presence of DNFX, and DNFX was observed in South Florida from fish collected in 1959. DNFX DNA was found in HFs at several locations in the Caribbean at a prevalence rate similar to that seen on low prevalence reefs in South Florida, although DNF is localized to Florida and the Bahamas. The sequences of DNFX throughout the Caribbean were found to be similar to those seen in South Florida, with the exception of DNFX from the Bahamas, which differed from the South Florida sequences by 2%. (10 base substitutions over 400 bases). In conclusion, DNFX was found to be significantly correlated with the presence of DNF tumors, and was found at significantly higher copy numbers in TFs and EFs than in HFs. DNFX was found in significantly more HFs on high prevalence reefs than on low prevalence reefs. DNFX was seen to be widespread in the Caribbean, and to have been present in South Florida since at least 1959, although at very low copy numbers. Finally, in the region sequenced in this study, DNFX was found to have almost no sequence variation among cell lines, TFs, HFs, EFs, or fish from elsewhere in the Caribbean. The copy number of DNFX (above 1 copy of DNFX per 25 cells), and not sequence variation, is likely to lead to the development of tumors in bicolor damselfish.</p>