A cytogenetical study on Economidichthys pygmaeus Holly, 1929 (Pisces, Gobiidae), an endemic freshwater goby from Western Greece.

A cytogenetic study was carried out on the chromosomes and the nuclear DNA content of the freshwater goby Economidichthys pygmaeus (Pisces, Gobiidae). The species is characterized by a 2n=46 karyotype consisting of 12 submetacentric and 11 subtelocentric chromosome pairs (NF=70). Major (45S) rDNA genes are terminal-centromeric located on the short arm of a single medium-small sized submetacentric pairas assessed by in situ hybridization, CMA3 staining, and Ag-NOR banding. The haploid (C-value) nuclear DNA content is 0.93±0.003 picograms. The cytogenetical data of Economidichthys pygmaeus were compared with those ones already available for other related gobies.

Classical and molecular cytogenetic characterization of allochthonous European bitterling Rhodeus amarus (Cyprinidae, Acheilognathinae) from Northern Italy.

A cytogenetical study was carried out on 34 specimens of the European bitterling Rhodeus amarus (Teleostei: Cyprinidae, Acheilognathinae) from four rivers of the Venice district (NE Italy). This allochthonous fish species was accidentally introduced in the North-East of Italy about 20 years ago and is now rapidly spreading all over the rivers of the Northern part of the country. All the studied specimens are characterised by the same karyotype (2n = 48: 8M + 20SM + 20ST), i.e., the typical one of the native populations of the species. However, a polymorphism in the number of NOR bearing chromosomes has been found. In fact, in addition to the main species-specific NORs, on the short arms of chromosome pair 7, two to five additional 18S rDNA sites have been revealed by FISH in different specimens. Sequential staining with silver nitrate, chromomycin A(3) and DAPI revealed that most of the additional sites are inactive and CMA(3)-positive. Data herein reported confirm that in spite of an overall morphological karyological conservativeness, significant differences for the finer cytogenetic features can be found within the Acheilognathinae with the 2n = 48 and NF = 76 karyotype.

Heterochromatin of the scarab beetle, Bubas bison (Coleoptera: Scarabaeidae) II. Evidence for AT-rich compartmentalization and a high amount of rDNA copies.

An unexpected result arising from a previous characterization of the scarab beetle Bubas bison (Coleoptera: Scarabaeidae) heterochromatin was its unusual homogeneous reaction to different staining methods. In particular, silver stainability of heterochromatic ends of all chromosomes prevented identification of the number of rDNA transcriptionally active regions. Data formerly obtained using silver impregnation (Ag-NOR), C- G- and DAPI banding are here improved and completed by application of CMA(3) staining and rDNA FISH with the aim to investigate heterochromatin base composition and locate rDNA regions with respect to NOR-associated heterochromatin. Our results show that B. bison has a high amount of heterochromatin (almost 50%) and that--as revealed by rDNA FISH--major rRNA genes are spread over the heterochromatic telomeric regions of eight chromosomes, thus suggesting that only a portion, although consistent, of total heterochromatin is associated with ribosomal clusters. Moreover, DAPI-positive (AT-specific) and CMA(3)-negative (GC-specific) reactions of heterochromatic DNA confirm its AT-rich composition. Finally, possible explanations for the bright DAPI-fluorescence of both heterochromatin and rDNA sequences are discussed.

Production and characterization of a continuous embryonic cell line from sea bass (Dicentrarchus labrax L.).

Continuous cell lines represent an important tool both for biological studies and for their applications in marine biotechnology. In this article we describe the production and characterization of a continuous adherent cell line, named DLEC, derived from early embryos of the European sea bass Dicentrarchus labrax L. (Actinopterygii, Moronidae). Cells were obtained by disrupting 2- to 12-hour-old embryos and culturing resulting cells at 18 degrees C in RPMI medium containing 5% fetal calf serum (FCS) and 10% supernatant fraction of the embryo homogenate. After 8 weeks culture medium was replaced with Liebovitz's L15 medium containing 10% FCS and DLEC cells started proliferation. Subsequently, they were continuously cultured until the 50th passage without evident changes in their morphology. DLEC cells show a fibroblast-like shape and a modal chromosome number of 48, as do the wild-type cells; conversely the constant presence of six to nine meta-submetacentric elements in the karyotype (vs. zero to two in the wild-type) indicates the occurrence of chromosomal rearrangements during stabilization. DLEC cells are sensitive to substances known to induce differentiation of mammalian cells such as retinoic acid and phorbol esters. They have been transfected using liposomes with a commercial plasmid vector containing a reporter gene, thus suggesting a possible importance as an alternative expression system of recombinant vertebrate proteins in teleost cells.

A microsatellite linkage map of the European sea bass Dicentrarchus labrax L.

A genetic linkage map of the European sea bass (Dicentrarchus labrax) was constructed from 174 microsatellite markers, including 145 new markers reported in this study. The mapping panel was derived from farmed sea bass from the North Adriatic Sea and consisted of a single family including both parents and 50 full-sib progeny (biparental diploids). A total of 162 microsatellites were mapped in 25 linkage groups. Eleven loci represent type I (coding) markers; 2 loci are located within the peptide Y (linkage group 1) and cytochrome P450 aromatase (linkage group 6) genes. The sex-averaged map spans 814.5 cM of the sea bass genome. The female map covers 905.9 cM, whereas the male map covers only 567.4 cM. The constructed map represents the first linkage map of European sea bass, one of the most important aquaculture species in Europe.

Cytogenetics of the land snails Cantareus aspersus and C. mazzullii (Mollusca: Gastropoda: Pulmonata).

A cytogenetic study was carried out on the chromosomes and nuclear DNA contents of the land snails Cantareus aspersus and C. mazzullii (Gastropoda: Pulmonata). Chromosomes were studied using Giemsa staining, banding methods and fluorescent in situ hybridization (FISH) with three repetitive DNA probes [18S rDNA, (GATA)(n) and (TTAGGG)(n)]. Results were very similar in the two species both showing (1) 54 bi-armed chromosomes [submetacentrics (SM) + metacentrics (M) + subtelocentrics (ST)]; (2) 10 terminal NORs after sequential application of rDNA FISH and silver staining; (3) uniform DNA fluorescence with CMA(3) and DAPI staining and (4) genomic composition considerably enriched both in highly- and moderately-repeated DNAs. The telomeric (TTAGGG)(n) sequence hybridized with the termini of all of the chromosomes in the two species. In spite of their apparent karyological uniformity, flow cytometry DNA assays showed that C. aspersus and C. mazzullii are characterized by different nuclear DNA content (C values are 3.58 and 3.08 pg, respectively) and slightly different base composition in their genomes. Present data on GS and AT% in C. mazzullii and C. aspersus confirm the trend toward high GS values and GC percentages among land snails.

Chromosomal location polymorphism of major rDNA sites in two Mediterranean populations of the killifish Aphanius fasciatus (Pisces: Cyprinodontidae).

The chromosomes of the Mediterranean killifish, Aphanius fasciatus from two populations, the Lagoon of Venice (LV, 15 specimens) and the Lagoon "Stagnone di Marsala" (Sicily) (SM, 48 specimens), have been investigated using conventional Ag-staining and fluorescent in situ hybridization (FISH) with 18S rDNA probe. The two methods revealed variation in the number of major rDNA sites ranging from 8 to 14 (LV) and from 1 to 4 (SM) per individual. The fact that each individual possessed its own number of sites implies that observed variation was structural. Moreover, overlapping of silver staining and FISH patterns demonstrated that all ribosomal genes were transcriptionally active in each specimen.

Haematological parameters in Umbrina cirrosa (Teleostei, Sciaenidae): a comparison between diploid and triploid specimens.

Haematological features were compared between diploid and triploid specimens of the ray-finned fish Umbrina cirrosa. No significant differences between diploids and triploids were reported in haematocrit and total haemoglobin concentration, but erythrocytes and thrombocytes were significantly greater in size in triploids. Glycaemia was significantly lower in diploids, whereas triploid erythrocytes were more resistant to osmotic stress. In triploids, a greater fraction of leukocytes was positive for alkaline phosphatase activity, when stimulated with Bacillus clausii spores, otherwise no significant increase of oxygen consumption was observed in triploid leukocytes after stimulation, based on assays for superoxide anions. Triploids were characterized by a lower concentration of circulating blood cells with a lower surface/volume ratio when compared with diploids. These features may lead to a general disadvantage of triploids in withstanding stress conditions: a situation that needs to be taken into account in aquaculture practice.