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Vitellogenin is the yolk protein precursor. Multiple vitellogenins identified in several teleosts have been attributed different roles in the control of egg buoyancy and in early embryonic vs. late larval nutrition. In this study, the cDNA encoding VtgAa was characterized in the Antarctic fish Trematomus bernacchii (suborder Notothenioidei). The sequence contains 4,964 nucleotides and encodes 1,629 amino acids of the precursor molecule. To gain insights into the evolution of vitellogenin in Antarctic fishes, we identified the partial sequence of vtgAb, and vtgAa and vtgAb partial sequences of five other notothenioids. The phylogenetic analysis highlighted a close correlation between the Vtg amino acid sequences of the six Antarctic species and VtgAa and VtgAb of other perciforms. Finally, analysis of the ratio of vtgAa to vtgAb expression, evaluated in T. bernacchii by real-time PCR, showed a considerably greater expression of vtgAa in different periods of austral summer., (. © 2010 Wiley-Liss, Inc.)

Two highly repeated DNAs, designated NmE1/NmE2 and NmE5, were identified by EcoRV digestion in the chiton Nuttallochiton mirandus (Mollusca: Polyplacophora). The comparison of the sequences obtained showed high similarity in 5' and 3' regions and the NmE5 sequence displayed an inserted sequence that might arise from a transposable element. Southern blotting analyses suggested a tandem organization of both satellite DNA families identified. Moreover, dot blot analyses, performed on several molluscan species, revealed a different degree of conservation of the repeated DNAs. Fluorescence in-situ hybridizations (FISH) on metaphase chromosomes showed that both satellite DNAs are located at centromeric regions.

We describe the karyotype, location of nucleolus-organizing regions (NORs) and heterochromatin distribution and composition in the Antarctic chiton Nuttallochiton mirandus. Specimens had a karyotype of 2n = 32 chromosomes, of which two were microchromosomes. Among macrochromosomes, the elements of the first and fourth pair were bi-armed, the others were telocentric. At least six NOR sites were detected with NOR-FISH, but only four were Ag-NOR-banding-positive. The two microchromosomes were essentially euchromatic, while all macrochromosomes exhibited clear pericentromeric C bands that were found to be AT-rich (being quinacrine- and DAPI-positive) and resistant to digestion with AluI and HaeIII. N. mirandus has the largest number of chromosomes (2n = 32) and telocentric elements (26) of all the chiton species studied to date. The karyological results of our study agree with previous molecular data indicating N. mirandus as a sister taxon of Acanthochitona crinita. The karyotypes of the two species could be related as a result of Robertsonian rearrangements. According to the more parsimonious hypothesis, the former would be the primitive karyotype, although other evolutionary events cannot be ruled out.

Synthesis of vitellogenin (VTG) in male fish is a widely recognized effect for estrogenic pollutants in temperate environments, while similar investigations are still lacking for Antarctic organisms. In this study, a preliminary characterization of vitellogenin gene expression was performed by RT-PCR in the key species Trematomus bernacchii sampled in different phases of reproductive cycle and food availability. Females exhibited the highest gene expression during the spawning period, but VTG mRNA was always detected also in males; a significant increase of gene expression was observed both in males and females at the end of the feeding season. These results were not fully supported by a differential exposure to phyto- or anthropogenic estrogens during the planctonic cycle; on the other side, the endocrine properties of cadmium, naturally elevated in Terra Nova Bay and increasing during algal bloom, would explain both the presence of VTG mRNA in males and the seasonal changes of gene induction. Laboratory exposures did not reveal short-term estrogenic effects of cadmium while an elevated responsiveness of T. bernacchii was observed toward a classical estrogenic receptor agonist (17beta-estradiol). Different hypotheses were considered to suggest delayed endocrine effects of cadmium, including the early interaction with other cellular detoxification systems or alterations at multiple levels of the hypothalamus-pituitary-gonad-liver axis. Although molecular mechanisms of VTG gene expression in males of T. bernacchii remain unclear, obtained results provide interesting insights on this species which should stimulate future research activities.

We report the presence of Tc1 transposon-like sequences in the Antarctic ice-fish Chionodraco hamatus, belonging to the Notothenioidei. The complete DNA sequence of these transposon-like elements is reduced in length compared to other Tc1 transposons, but it appears to share significant structural similarities with them. It contains a degenerate open reading frame, whose inferred 264 amino acid sequence shares sequence similarity with the 'aspartic acid, aspartic acid (35) glutamic acid' family of transposases, particularly those from Caenorhabditis species (sp.) and Drosophila sp. Southern blot analysis and polymerase chain reaction amplification indicate that Tc1 transposon-like sequences are present in other notothenioid species, though their amount can vary in the different lineages.