Isolation and characterization of a retrovirus from the fish genus Xiphophorus

Neoplasia in fishes

Similar to higher vertebrates, neoplasia is not an uncommon disease in fishes, which are the largest group of vertebrates. However,neoplasia in fishes is generally a benign condition with relatively few exceptions of malignant disease. The objective of this discussion is to provide an overview of neoplasia and the various neoplastic disease conditions in fishes according to organ system,including the few neoplasms of species that are familiar to the aquatic animal or exotic animal practitioner. The discussion also considers the various nonneoplastic lesions in fishes that may be confused with neoplasms, and treatment of neoplastic disease in fishes that is generally restricted to surgical intervention.

Viruses of lower vertebrates

Viruses of lower vertebrates recently became a field of interest to the public due to increasing epizootics and economic losses of poikilothermic animals. These were reported worldwide from both wildlife and collections of aquatic poikilothermic animals. Several RNA and DNA viruses infecting fish, amphibians and reptiles have been studied intensively during the last 20 years. Many of these viruses induce diseases resulting in important economic losses of lower vertebrates, especially in fish aquaculture. In addition, some of the DNA viruses seem to be emerging pathogens involved in the worldwide decline in wildlife. Irido-, herpes- and polyomavirus infections may be involved in the reduction in the numbers of endangered amphibian and reptile species. In this context the knowledge of several important RNA viruses such as orthomyxo-, paramyxo-, rhabdo-, retro-, corona-, calici-, toga-, picorna-, noda-, reo- and birnaviruses, and DNA viruses such as parvo-, irido-, herpes-, adeno-, polyoma- and poxviruses, is described in this review.

Highly sensitive qualitative and quantitative detection of reverse transcriptase activity: optimization, validation, and comparative analysis with other detection systems

An ultra-sensitive assay for reverse transcriptase (RT) activity called Amp-RT has been developed. An in vitro transcribed heteropolymeric RNA sequence was used as a template, and polymerase chain reaction (PCR) amplification with Southern-blot hybridization served as a detection system for the cDNA product of the reaction. Titration of Mg2+ and Mn2+ concentrations using the human immunodeficiency virus type 1 (HIV-1) and the human T lymphotropic virus type 1 (HTLV-I), respectively, showed optimal assay reactivity for both viruses at 2-20 mM of Mg2+. Analysis of density banded HIV-1 showed that the peak RT activity of the assay was associated with the fractions consistent with retrovirus particles. The sensitivity of Amp-RT was also compared with that of three conventional RT assays by using seven different retroviruses including HIV-1, simian immunodeficiency virus (SIV), caprine arthritis-encephalitis virus (CAEV), HTLV-I and HTLV-II, simian retrovirus type 2 (SRV-2), and gibbon ape leukemia virus (GALV). HTLV-I, HTLV-II, and GALV could not be detected by the three conventional RT assays. Amp-RT was able to detect all these viruses in 10(1)-10(3)-fold dilutions. Similarly, Amp-RT was found to be 10(3)-10(6)-fold more sensitive than the other RT assays in detecting HIV-1, SIV< or CAEV. Culture supernatants from uninfected cell lines were all Amp-RT negative. A quantitative Amp-RT assay was also developed by using recombinant HIV-1 RT and signal quantitation. The assay was found to have a 5 log linear range, and therefore, provides a useful tool for quantitating RT and retroviruses. Amp-RT offers a sensitive generic tool for the qualitative and quantitative detection of known and unknown retroviruses.

Gypsy/Ty3-class retrotransposons integrated in the DNA of herring, tunicate, and echinoderms

Eight new examples of retrotransposons of the Gypsy/Ty3 class have been identified in marine species. A 525-nt pol gene-coding region was amplified using degenerate primers from highly conserved regions and has extended the range of recognition of Gypsy/Ty3 far beyond those previously known. The following matrix shows the percentage AA divergence of the translations of this segment of the pol gene coding region. [table: see text] The underlines separate three groups of retrotransposons that can be recognized on the basis of this amino acid sequence. The new upper group shows surprising amino acid sequence similarity among members from the DNA of herring, sea urchin, starfish, and a tunicate. For example, the herring element differs by only 41% from the Ciona element and 46% from the sea urchin element. The group between the lines includes members close to previously known elements (marked by asterisks) and has so far been found only in sea urchins. The two upper groups differ from each other by 55-60% and yet members of both groups (e.g., Spr1 and Spr2) are integrated into the DNA of one species--S. purpuratus. Below the lower underline is listed the only known representative of a very distant group, which occurs in starfish DNA. In spite of large divergence, amino acid sequence comparisons indicate that all of the elements shown in the array are members of the LTR-containing class of retrotransposons that includes Gypsy of Drosophila and Ty3 of yeast. Of all known mobile elements this class shows the closest sequence similarity to retroviruses and has the same arrangement of genes as simpler retroviruses.

Increasing melanoma incidence: putatively explainable by retrotransposons. Experimental contributions of the xiphophorine Gordon-Kosswig melanoma system

The worldwide accelerating increase of neoplasia in humans is difficult to explain. We use the Xiphophorus tumor model to approach this problem by melanoma provocation with X-rays. Melanoma develops following inappropriate expression of x-erb B-conducted developmental genes and their controllers. These oncodeterminants are inherited according to Mendelian rules. We detected a new type of oncodeterminants that, following a single treatment of embryos with X-rays, generates a self-generating non-Mendelian melanoma transmission and accelerating increase of its incidence in succeeding generations (e.g., 0-->18-->33-->52%). To localize these oncodeterminants, we crossed nonirradiated fish having half of their chromosomes irradiated with nonirradiated fish having none of, half of, or all of their chromosomes irradiated. Because tumor rate and expression in the following generations correspond to the rates of treated chromosomes, we conclude that the new oncodeterminants are distributed over the chromosomes of the fish, where they may increase in the changing generations. By means of xiphophorine-specific retroviral DNA, we isolated two retrotransposons that behave hereditarily like the new transgenerational oncodeterminants. Sequence analysis revealed three ORFs flanked by LTRs containing motives of regulatory sequences typical for known retroviral and retrotransposal LTRs. Pol- and env-resembling sequences are lacking. Southern and in situ hybridization showed their multiple and repetitive nature distributed throughout the chromosomes and indications for their capability to increase in number without further treatment. Their transcripts are expressed in concert with those of most of the other known xiphophorine tumor determinants. Their expression is extremely high in cell cultures from tumorous embryos derived from ancestors treated as embryos with X-rays.