Etho-biochemical mechanisms of early differentiation in juveniles of the Atlantic salmon <Emphasis Type="Italic">Salmo salar</Emphasis>

The social status of hatchery-reared juveniles of Atlantic salmon Salmo salar at the age of 11–19 months in conditions of lack of shelters was investigated experimentally. It was demonstrated that biochemical differentiation in such juveniles begins at the age of 13 months—one month before the first differences in the social status of fish and four months prior to the beginning of smoltification. The dominants occupy bottom areas with shelters and extrude the subordinates to the water column. The subordinates undergo smoltification or die from aggression of the dominants. Concentrations of dopamine, noradrenalin, and of their metabolites in the brain of fish in the beginning of smoltification were higher in the dominants and, by the end of smoltification, were higher in smolts. The social behavior of fish is considered to be one of the ethological mechanisms of differentiation of salmon juveniles into smolts and parr.     

Distribution of fish in the complex of floodplain-riverbed biotopes of the Irtysh

Distribution, composition, and movements of fish within the floodplain-riverbed complex of the Lower Irtysh are investigated. The principal working tools were hydroacoustic computerized complexes for the detection of fish aggregations and of their movements in the floodplain water course. Twenty-four-hour hydroacoustic observations revealed the predominantly crepuscular-nocturnal type of activity of most fish and the mass downstream migration of juveniles at the onset of the night. Seasonal traits of formation of fish aggregations on key biotopes of the Irtysh are revealed, and their biological harmony is shown. The necessity that fish distribution should be analyzed as a dynamic phenomenon is shown.     

Identification and characterization of acetyl-CoA carboxylase gene cluster in <Emphasis Type="Italic">Streptomyces toxytricini</Emphasis>

The gene locus for acetyl-CoA carboxylase (ACC) involved in the primary metabolism was identified from the genomic library of Streptomyces toxytricini which produces a lipase inhibitor lipstatin. The 7.4 kb cloned gene was comprised of 5 ORFs including accD1, accA1, hmgL, fadST1, and stsF. In order to confirm the biochemical characteristics of AccA1, the gene was overexpressed in Escherichia coli cells, and the recombinant protein was purified through Ni²⁺ affinity chromatography. Because most of the expressed AccAl was biotinylated by host E. coli BirA in the presence of D-biotin, the non-biotinylated apo-AccA1 was purified after gene induction without D-biotin, followed by exclusion of holo-AccA1 using streptavidin beads. The separated apo-AccA1 was post-translationally biotinylated by S. toxytricini biotin apo-protein ligase (BPL) in a time- and enzyme-dependent manner. This result supports that this gene cluster of S. toxytricini encodes the functional ACC enzyme subunits to be biotinylated.     

Sarcomere dynamics in skeletal muscle myofibrils during isometric contractions

The main goal of this study was to evaluate the dynamics of sarcomeres during isometric activation of skeletal muscle myofibrils. Rabbit psoas myofibrils (n=14) were attached between a pair of cantilevers for force measurements at one side and a rigid glass needle at the other side, and their images were used for measurements of individual sarcomere lengths (SL) during contractions. Myofibrils were set at average SL between 2.13 and 3.06 μm, and were activated and held isometric for 20–35 s during which SL and force were continuously measured. SL dispersion increased from the rest state to activation, but it remained mostly constant during the activation period. Even with the length non-uniformity developed during myofibril activation, most sarcomeres stabilized their length changes during the isometric contraction. As a result, sarcomeres contracted at different degrees of filament overlap while producing similar forces. When the myofibrils were separated in two groups that produced force at averaged short (≤2.5 μm) or long (≥2.5 μm) SL, the initial non-uniformity was greater in long lengths, but changes observed in sarcomeres during the activation period were similar, suggesting that sarcomere stability is not length-dependent.     

Evidence that errors made by DNA polymerase alpha are corrected by DNA polymerase delta

Eukaryotic replication begins at origins and on the lagging strand with RNA-primed DNA synthesis of a few nucleotides by polymerase alpha, which lacks proofreading activity. A polymerase switch then allows chain elongation by proofreading-proficient pol delta and pol epsilon. Pol delta and pol epsilon are essential, but their roles in replication are not yet completely defined . Here, we investigate their roles by using yeast pol alpha with a Leu868Met substitution . L868M pol alpha copies DNA in vitro with normal activity and processivity but with reduced fidelity. In vivo, the pol1-L868M allele confers a mutator phenotype. This mutator phenotype is strongly increased upon inactivation of the 3' exonuclease of pol delta but not that of pol epsilon. Several nonexclusive explanations are considered, including the hypothesis that the 3' exonuclease of pol delta proofreads errors generated by pol alpha during initiation of Okazaki fragments. Given that eukaryotes encode specialized, proofreading-deficient polymerases with even lower fidelity than pol alpha, such intermolecular proofreading could be relevant to several DNA transactions that control genome stability.     

Cooperative effects of cofilin (ADF) on actin structure suggest allosteric mechanism of cofilin function

Using site-specific fluorescence probes and cross-linking we demonstrated that cofilin (ADF), a key regulator of actin cellular dynamics, weakens longitudinal contacts in F-actin in a cooperative manner. Differential scanning calorimetry detected a dual nature of cofilin effects on F-actin conformation. At sub-stoichiometric cofilin to actin ratios, cofilin stabilized sterically and non-cooperatively protomers at the points of attachment, and destabilized allosterically and cooperatively protomers in the cofilin-free parts of F-actin. This destabilizing effect had a long range, with one cofilin molecule affecting more than 100 protomers, and concentration-dependent amplitude that reached maximum at about 1:2 molar ratio of cofilin to actin. In contrast to existing models, our results suggest an allosteric mechanism of actin depolymerization by cofilin. We propose that cofilin is less likely to sever actin filaments at the points of attachment as thought previously. Instead, due to its dual structural effect, spontaneous fragmentation occurs most likely in cofilin-free segments of filaments weakened allosterically by nearby cofilin molecules.     

Downstream migration in ammocoetes of the Arctic lamprey <Emphasis Type="Italic">Lethenteron camtschaticum</Emphasis> in some Kamchatka rivers

This paper considers the major patterns of downstream migration in Arctic lamprey ammocoetes in Kamchatka rivers. Ammocoetes of different age groups are shown to be constantly noted in the composition of the migrant part of a river community. The greatest intensity of downstream migration in ammocoetes of the age class 0+ is noted in the period of their primary dispersion in late July-early August. The ammocoetes of the age groups 1+ and older migrate from spring to late autumn, but their concentrations are not high. The significant similarity of such a biologic feature as downstream migration in ammocoetes and juvenile salmonids serves as an example of ecological analogy.     

Reproduction and initial development of manybar goatfish <Emphasis Type="Italic">Parupeneus multifasciatus</Emphasis> (Mullidae)

Features of reproductive biology and the stages of early ontogeny are described in the mass tropical species manybar goatfish Parupeneus multifasciatus. In general, in the catches represented by mainly sexually mature fishes, females prevail but males prevail in the largest size classes. The females reach their first sexual maturity by approximately 110 mm fork length, and they are characterized by continuous oogenesis and egg deposition in batches. The fish spawn over the entire year with a trend to lower values of the gonadosomatic index (GSI) of the females from June to October. The features of early ontogeny are compared in manybar goatfish and red mullet Mullus barbatus ponticus from the Black Sea.     

Population structure of arctic lamprey <Emphasis Type="Italic">Lethenteron camtschaticum</Emphasis> from the Kol River (Western Kamchatka)

Phenetic diversity is investigated and the taxonomic status of lampreys (Petromyzontidae) from the Kol basin (Western Kamchatka) is verified. Typically anadromous lamprey, anadromous lamprey forma praecox, resident lamprey, smolts, and larvae of lamprey are discovered and described. Their comparative analysis is made by standard morphometric characters. Differences between the forms by plastic characters depend on size and weight. No significant differences are found by major taxonomic characters between the forms of anadromous and resident lampreys which would indicate their taxonomic separation. Phenetic types of spawners are representatives of the population of one complexly structured species represented by life forms realizing different life history strategies (anadromous and resident), and belong to the species Arctic lamprey Lethenteron camtschaticum (Tilesius, 1811).