Elisabetta Coluccia

Major and 5S ribosomal sequences of the largemouth bass Micropterus salmoides (Perciformes, Centrarchidae) are localized in GC-rich regions of the genome

Major and 5S ribosomal genes have been localized in the chromosomes of Micropterus salmoides. By C-banding, Ag-staining, CMA3-staining and 45S and 5S fluorescence in-situ hybridization (FISH), we demonstrate that the 45S and 5S ribosomal genes are clustered in two different chromosome pairs and both are located in heterochromatic GC-rich regions. PCR amplification and sequencing of the 5S intergenic non-transcribed sequences have allowed us to identify variability essentially due to a trinucleotide tandem repeat (GCT).

Replication banding in two Mediterranean moray eels: chromosomal characterization and comparison

Early and late replication bandings have been obtained by in vitro BrdU incorporation in the Mediterranean Muraenidae species Muraena helena and Gymnothorax unicolor, and used to characterize their karyotypes. A comparative analysis of the banding patterns allowed to point out high karyotype similarity as well as chromosome rearrangements that occurred in karyotype evolution between these species.

Colocalization of the ribosomal gene families in Conger conger (Anguilliformes, Congridae)

The location of the major and minor ribosomal gene families in the conger eel (Conger conger) was investigated by in situ hybridization and CMA3 staining. The two gene families were localized in only one chromosome pair, on the short arm of pair 19, in an entirely CMA3‐positive region. Among the Anguilliformes, C. conger is the only species that shows the presence of the two gene families in the same chromosomal region.

B chromosomes in Crustacea Decapoda

Among crustacean Decapoda numerical chromosome variability is frequent, and it has been hypothesized that the presence of supernumerary chromosomes accounts for this variability. Thanks to the improvement of cytogenetic analysis by chromosomal banding techniques, supernumerary B chromosomes (Bs) have been demonstrated in Nephrops norvegicus, Homarus americanus,Palinurus elephas and P. mauritanicus, belonging to different crustacean families. In all four species Bs were variable in number, mainly heterochromatic and undigested by various endonucleases, and in meiosis they showed non-Mendelian segregation. Compared to the other chromosomes of the complement, the Bs are very small in almost all species, but some of them were very large in N. norvegicus.

Karyotype, C- and G-banding, and nucleolar organizer regions of Conger conger (Osteichthyes, Anguilliformes)

Abstract The diploid chromosome number of Conger conger L. was found to be 2n = 38, with the karyotype consisting of four pairs of metacentric, two of submetacentric and thirteen of acrocentric chromosomes. C‐ and G‐banding allowed the identification of homologous chromosomes. NOR was identified on the short arm of the smallest acrocentric pair.

Identification of two new repetitive elements and chromosomal mapping of repetitive DNA sequences in the fish Gymnothorax unicolor (Anguilliformes: Muraenidae).

Muraenidae is a species-rich family, with relationships among genera and species and taxonomy that have not been completely clarified. Few cytogenetic studies have been conducted on this family, and all of them showed the same diploid chromosome number (2n=42) but with conspicuous karyotypic variation among species. The Mediterranean moray eel Gymnothorax unicolor was previously cytogenetically studied using classical techniques that allowed the characterization of its karyotype structure and the constitutive heterochromatin and argyrophilic nucleolar organizer regions (Ag-NORs) distribution pattern. In the present study, we describe two new repetitive elements (called GuMboI and GuDdeI) obtained from restricted genomic DNA of G. unicolor that were characterized by Southern blot and physically localized by in situ hybridization on metaphase chromosomes. As they are highly repetitive DNA sequences, they map in heterochromatic regions. However, while GuDdeI was localized in the centromeric regions, the GuMboI fraction was distributed on some centromeres and was co-localized with the nucleolus organizer region (NOR). Comparative analysis with other Mediterranean species such as Muraena helena pointed out that these DNA fractions are species-specific and could potentially be used for species discrimination. As a new contribution to the karyotype of this species, we found that the major ribosomal genes are localized on acrocentric chromosome 9 and that the telomeres of each chromosome are composed of a tandem repeat derived from a poly-TTAGGG DNA sequence, as it occurs in most vertebrate species. The results obtained add new information useful in comparative genomics at the chromosomal level and contribute to the cytogenetic knowledge regarding this fish family, which has not been extensively studied.

Cytogenetic characterization of the moray eel Gymnothorax tile and chromosomal banding comparison in Muraenidae (Anguilliformes)

Abstract The karyotype of the teleostean Gymnothorax tile was analysed by replication banding in order to clearly identify the homologous chromosomes. The RBG pattern was then compared to those of the other Muraenidae studied (G. unicolor and Muraena helena) and banding homologies of nine chromosome pairs were pointed out. A single nucleolar organizer region (NOR) was localized by FISH, silver- and CMA3-staining on the short arm of the pair 12. Telomeric (TTAGGG) repeats were terminally localized by FISH on all the chromosome pairs. The genome size and the AT-DNA content were evaluated by flow cytometry. Available cytogenetic data on the Muraenidae were then compared and discussed.

Mitotic and meiotic chromosomes of the American lobster Homarus americanus (Nephropidae, Decapoda)

The chromosomes of H. americanus have been characterised by C-banding, fluorochrome banding and restriction endonuclease banding. Thanks to these techniques, it has been possible to identify mitotic and meiotic figures clearly and to study the distribution and structure of heterochromatic regions. Moreover, we have identified small supernumerary chromosomes, variable in number and often asynaptic in first meiotic metaphase.

Study of the nucleolar organizer regions in Palinurus elephas (Crustacea: Decapoda)

Using fluorescence in situ hybridization (FISH), chromomycin (CMA3) staining and silver staining, we studied the nucleolar organizer regions in the spiny lobster Palinurus elephas in order to extend our knowledge on the karyology of this commercially important species. Multiple NORs have been detected by FISH, and CMA3 showed a good correspondence between the localization of GC-rich heterochromatin and the ribosomal genes mapped by FISH. In contrast, the number of Ag-positive regions was higher than the number of FISH and CMA3 signals, which may be explained by silver staining of the kinetochores. A variability in the number of FISH and CMA3 signals has been detected in metaphases I and II which is probably due to the occurrence of rDNA cistrons on B chromosomes.

CYTOGENETIC AND MOLECULAR CHARACTERISTICS OF ATLANTIC EELS (ANGUILLA ANGUILLA AND A. ROSTRATA) GENOME

Abstract The Atlantic eels, Anguilla anguilla and A. rostrata, have partially overlapping spawning sites and show incomplete reproductive isolation as testified by the presence of hybrids at low frequency. Nevertheless, significant genetic differences between the two species have been pointed out by data on biochemical polymorphisms and mitochondrial DNA. This study reviews the cyto‐genetic and molecular data and points out differences and similarities between the two species.