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Xiphophorus andersi n. sp. from the Rio Atoyac, Vera Cruz, Mexico is described: lang head, moderately slender body, large dark black spar at the basis of the anal fin; adult male with short sword-like caudal appendage; rip of ray 5a of gonopodium without a developed claw. Xiphophorus andersi n. sp. differs by the combination of distinct characters from all the other species of the genus known so far. The new species shows features of both the so-called platyfish species group and the so-called swordtail species group.
Melanotic melanoma (MM) of Xiphophorus (Teleostei: Poeciliidae) was studied by conventional preparations and freeze-etch preparations for electron microscopy. MM of Xiphophorus exhibits tightly packed pigment cells with prominent dendritic processes and interdigitations of their plasma membranes. The most impressive feature of MM cells is the occurrence of Iarge lobulated nuclei with numerous nuclear pores and some nuclear pockets. Abundant spheroidal or ellipsoidal melanosomes (diameter 200-650 nm) and vesicular structures are distributed throughout the cellular dendrites, whereas the perinucJear cytoplasm is free of melanosomes.
A further characteristic feature of melanoma cells in fish is the occurrence of melanosome complexes (i.e., "compound melanosomes"). These melanosome complexes consist of a few to numerous melanosomes, which are enveloped by a separate rnembrane. Pinocytotic vesicles couJd be demonstrated with distinct differences in frequency and distribution patterns, indicating differences in the metabolic activities of the cells in the same melanoma. Intercellular junctions are lacking in the MM cells.
The conventional TEM technique showed clear advantages in the demonstration of intemal architecture of organelles, whereas FE bad considerable potential in respect to the visualization of membrane surface specializations.
The expression of the c-src gene in embryonie and adult tissue of the teleost fish Xiphophorus helleri was analyzed by in-situ hybridization. The highly conserved fish c-src gene was found to be expressed at high levels in midterm embryos, where c-src mRNA was localized in developing neurons of the sensory layer of the differentiating retina and in the developing brain. In adult tissues the expression of c-src was found to persist in certain cell types of the brain and the neural retina, especially in the bipolar cells of the inner nuclear layer, which are postmitotic, fully differentiated mature neurons. Thus c-src in Xiphophorus appears to be a developmentally regulated proto-oncogene which is important for neuronal differentiation during organogenesis, but whose persistence of expression in certain terminally differentiated neurons strongly suggests a particular maintenance function for c-src in these cells as well.
In Xiphophorus the causative, primary cellular oncogene for melanoma formation has been assigned by classical genetics to a sex-chromosomal locus, designated Tu. Activation of Tu was proposed to be the result of the elimination of Tu-specific regulatory genes which normally suppress the transforming function in the nontumorous state. In order to understand the role which known proto-oncogenes migbt play in this process, we have analysed the expression of src, erb A, erb B, ras, abl, sis and mil related genes from Xiphophorus during embryogenesis, in non-tumorous organs and in melanoma cells. For src, ras, erb B and sis a differential expression during embryogenesis and/or in normal organs was detected, with preferential expression of src in neural tissues, a high abundance of sis transcripts in an embryonal epitheloid cellline and of erbB transcripts in the head nephros. In melanoma cells ras, src and a v-erb B related gene were found to be expressed. The src gene most likely is more involved in secondary processes during tumor progression, while the expression of the v-erb B related gene might be transformation-specific because recently such a sequence was found to map to the close vicinity of the Tu-locus.
Melanoma formation in the poeciliid fish Xiphophorus is mediated primarily by a cellular oncogene, designated Tu. Elimination of Tu-specific genes releases the transforming function of Tu and leads to melanoma formation. Southern blot analyses revealed a tight linkage of a v-erb B related gene to the Tu-locus and Northern blot analyses of RNA of solid melanomas indicated a coordinated deregulation and for mutational activation of several oncogenes. In order to get a better insight into the regulation of oncogene expression in normal and transformed cells of Xiphophorus, we studied the expression of Xsrc, Xras, Xmyc, Xerb A, Xsis, and the v-erb B related gene in a melanoma derived cell line (PSM) and an embryonic cell line (A2) under conditions of low growth factor supply. Both celllines express the Xsrc, Xmyc, and Xras genes, while PSM cells in addition express the v-erb B related gene and A2 cells the Xsis gene. In PSM cells serum deprivation leads to an accumulation of most of the oncogene mRNAs analysed. This is most apparent for a 5.0 kb transcript of the v-erb B related gene, probably due to an increase in transcript stability. The levels of these mRNAs returned to normal within 2h after stimulation with 10% fetal calf serum. At the protein level we observed an initial decrease followed by an increase of the n-p60c-src kinase (the protein product of tbe Xsrc gene) activity in cells deprived of serum. Serum stimulation restored a normal pp60"-src kinase activity. In contrast serum deprivation of A2 cells reduced the transcript amounts of each of the oncogenes analysed. The same holds true for one beta-tubulin transcript, while the level of a second beta-tubulin transcript was unaffected. Serum stimulation led to a reactivation of Xras and Xsrc after a delay of approximately 48b. The pp60(c-src) kinase activity was found to be 6-10 times lower as compared to the PSM cells and did not differ between serum deprived and serum stimulated cells. Enzyme activities and isoenzyme patterns of several glycolytic enzymes were found to be not affected by serum deprivation and stimulation in both celllines.