The distribution of (TTAGGG)n telomeric repeats was studied in chromosomes of two Atlantic eels, Anguilla anguilla and A. rostrata. We found that these sequences hybridize to all the telomeres but also to the entire nucleolar organizer region (NOR) localized in both species at the short arm of chromosome 8. This was considered to be due to the interspersion of telomeric sequences within the NOR ones. Whatever the significance of this interspersion may be, it seems to be limited to A. anguilla and A. rostrata since in Muraena helena (family muraenidae), which also belongs to the Anguilliformes, no telomeric hybridization signals were found along the NOR regions.

No abstract

We investigated the chromosome complement of Muraena Helena L. using C-banding, nucleolar organizer region silver staining, and restriction endonuclease digestion. We found a diploid number identical to that previously found in other Muraenidae (2n = 42). C-banding revealed the presence of constitutive heterochromatin in the centromeres of all chromosomes as well as in most telomeres of acrocentric chromosomes. Nucleolar organizer regions were detected only on the short arm of chromosome 7. Digestion with either HaeIII, MboI, or DdeI restriction endonucleases produced a clearcut, specific banding pattern for each enzyme and indicated the existence of at least two different classes of highly repetitive DNAs. The short arm of chromosome 7 varied in size and staining characteristics.

Stick insects have been studied mainly for non-conventional reproduction modes, such as parthenogenesis, hybridogenesis and androgenesis. Parallel karyological investigations have evidenced extensive numerical and structural chromosome re-patterning, particularly evident in hybrid parthenogenetic taxa. Chromosome sets of bisexual Leptynia (Pantel) species show an evolutionary trend from 40 to 36 chromosomes and are characterized by cytological satellites of variable size and localization. We performed fluorescence in situ hybridization (FISH) analysis using 45S ribosomal genes and pentameric (TTAGG)n telomere sequences as probes in two strictly related but karyotypically distinct species, L. montana Scali (2n = 38/37; XX/XO) and L. attenuata Pantel (2n = 36). L. attenuata has recently been split into three subspecies (L. attenuata attenuata, L. attenuata iberica and L. attenuata algarvica), and found to share an XX/XY sex chromosome formula, unusual for stick insects. FISH by 45S rDNA sequences consistently labelled the short arm of the 4th chromosome pair, often of a variable size. Silver staining showed that nucleolar organizer regions (NORs) are active. FISH of the telomeric repeats, besides ordinary telomeres, also labelled the short arm of this same pair. The use of both probes in double FISH analysis fully confirmed the co-localization of ribosomal and telomeric highly repeated sequences. Since it is increasingly emerging that the co-localization of NORs and telomeric sequences appears to be a feature shared by evolutionarily distant animals, its possible role is discussed.

The diploid chromosome number of Gymnothorax unicolor (Delaroche, 1809) is 2n=42, the karyotype comprising six pairs of meta-submetacentric and fifteen pairs of acrocentric chromosomes. C-positive chromatin is present in the centromeres of all chromosomes as well as in the paracentromeric regions of some chromosomes. A nucleolar organizer region was identified on the long arm of chromosome 9, near the centromere. This region is also positive to C-banding.Cytotaxonomical relationships are evidenced between the described karyotype and that of the related species Muraena helena.

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.

Concerning thc number and type of the hemoglobin componcnts, the morny M u r u~i t i~ heleiia is characterized by three diffcrcnt phenotypes whose frequencies arc ncarly identical. Thus, the cathodal cornponent is present in all individuals, whereas one or both of two anodal components may be present in the same phenotype. These components have been separated by chromatography.The oxygen binding properties of the purified hcmoglobin components have been studied in the ahse,nce and presence of saturating concentrations of ATP or GTP and as a function of pH. The cathodal component shows an intrinsic 0, affinity four times higher than that of both aiiodal components, : I very sinall Bohr effect and a significant decrease in affinity upon addition of ATP and GTP (three and four times respectively with respect to stripped conditions), the latter being more cffcctivc than the former over the entire pH range exainincd. The anodal components do not appear functionally distinguishable and show the presence of iiii enhanced Bohr effect (Root effect) that is under the strict control of niicleotide triphosphates ATP, GTP, which, unlike in the cathodic component, cxert the same effect on oxygen affinity. The complete sequence of the chains of the cathodal iind of one of the anodal components have been determined.The possible molecular basis of these different functional characteristics are discussed in thc light of the globiii scquence and of thosc amino acid residues which are known to be responsiblc of hemoglobin functional behaviour.Krywords: hemoglobin ; oxygen binding; heterotropic interactions; uniino acid sequence ; moray.Comparative studies on Hb function havc ii special interest since they may lead to an understanding of those changes which, in the course of cvolution, have rtevcloped in different organisms to meet specific physiological requirements. In fact, besides contrihuting to a verification of the generality of the molecular mechanisms proposed for mammalian Hbs, a coniparativc approach may yield inforination on the kcatures involved in the evolutionury processes. In this respect, Hbs exhibit a great dcal of variation in terms of absolute affinities for oxygen and in their susceptibility to metabolic effectors such as 2,3-bisphosphoglycerale, ATP and GTP. This type ol' fine tuning is devcloped to i l high degree in all vertebratc Hbs and is primarily based on the ability of the cffector to preferentially bind one of the lwo qiiaternary conformations ('I and R slates in the simplrst modcl).Along thesc lines, specks having inultiple Hbs in their blood are of intercst i n so fiir as multiplicity of components is an evolutioxary response to the special needs of the individual. In fact, structural multiplicity is very often accompanied by i l niore or less marked fiinclional heterogeneity that has to be linked to sonic specific physiological rcquirements of the species. Hence, studies on Hb multiplicity may provide valuable information on structurc/fiinction relationships in gas-binding proteins and on ('cim.~l,o...

We have studied fixed chromosomes and purified DNA of Anguilla anguilla L. after digestion with HaeIII, AluI, MboI, and DdeI restriction endonucleases. Our data demonstrated (i) confirmation of the heteromorphic nature of NORs, (ii) absence of detectable sex chromosomes, and (iii) presence of discrete intercalary domains in this species. Our data also permitted us to hypothesize the existence of highly repetitive DNAs, localized in specific heterochromatic regions of A. anguilla chromosomes