Swimming response of goldfish,Carassius auratus,and the tetra,Hemigrammus caudovittatus,larvae to individual food items and patches

Synopsis Swimming speed and swimming path of goldfish and tetra larvae were studied in aquaria containing food patches composed of decapsulated cysts and immobilized nauplii of Artemia salina or sparsely distributed prey. The mean swimming speed of starved larvae in the medium without food was about four times higher than the speed of larvae feeding in a patch. Satiated larvae swam about 1.5 times slower than hungry fish. Consumption of single prey items by starved larvae caused the following sequence of swimming responses: handling pause (cessation of swimming), slow swimming in a restricted area, and fast swimming (approximately twice as fast as hungry larvae before encountering food) accompanied by a widening of the area searched (area increased searching). Mean swimming speed was constant over a broad range (10¹–10³ ind·1^–1 of food density, although at extreme (high or low) values of food density it depended on swimming responses of the predator. Frequency of visits to the different parts of the aquarium strongly depended on encounters of hungry fish with food particles or patches.     

Monoclonal antibodies modify acetylcholine-induced ionic channel properties in cultured chick myoballs

Summary Monoclonal antibodies directed against the cholinergic binding site of the acetylcholine receptor were found to alter the ion channel properties in cultured chick myoballs. Time and dose dependent reduction in acetylcholine sensitivity was observed. Noise analysis experiments indicated a decrease in the mean single channel conductance and an increase in the mean single channel open time.     

Effect of lowered incubation temperatures on nucleic acid and protein synthesis by a mesophilic and a psychrophilic bacterium

The authors studied changes in the synthesis of nucleic acids (RNA, DNA) and protein by a mesophilic strain ofEscherichia coli B and a psychrophilic strain ofPseudomonas fluorescens at a low incubation temperature giving tenfold prolongation of the generation time. It was found that lowering the incubation temperature was followed by an increase in the intracellular nucleic acid content during the lag phase and the phase of accelerated growth, in which maximum nucleic acid (NA) values were reached. As a result, the total NA level in the cell also remained relatively high during further proliferation, when the increase in NA (particularly RNA) slows down at low incubation temperatures. Proteosynthesis, however, fell in the mesophilic culture. The smaller effect of a lowered temperature on DNA biosynthesis was manifested specifically in the lag phase ofEscherichia coli, in which disproportion developed between the amount of DNA (which was synthesized at a relatively higher rate) and RNA; this was afterwards equalized by a temporary break in DNA production. Pronounced differences in the given types of biosynthesis were found only in the mesophilic culture, while at suboptimal temperatures the metabolism of the psychrophilic strain slowed down but no marked changes occurred.     

Comparative x-ray diffraction study of the crystalline lens in a number of vertebrates including man

X-ray diffraction method has been applied for comparative investigation of native structure of eye lens proteins (crystallins). X-ray diffraction patterns of the whole lenses and/or their nuclear parts were obtained for man and vertebrate animals. Crystalline lenses of the fishes Acerina cernua and Pelmatochromis kribensis, frog Rana temporaria, bull and man contain crystallins with a very similar secondary and tertiary structure, whereas lenses of chicks and the tortoise Testudo horsfieldi contain mainly crystallins with other structure. The results obtained reveal evolutionary conservatism of crystallin structure in fishes, amphibians and mammals. It was also concluded that there is no correlation between crystallin structure of the lens, elasticity of the latter and accommodation mechanism.     

Selection and mutant properties of Pichia guilliermondii yeasts with derepressed GTP cyclohydrolase, the enzyme of the 1st step in flavinogenesis

A positive method is proposed for selecting Pichia guilliermondii mutants with derepressed GTP cyclohydrolase. Mutants with the incompletely blocked gene RIB2 were used as parent strains; these can grow in a medium without riboflavin (RF) only if the enzyme is derepressed as the result of iron deficiency in cells. Strains growing in a medium without RF at the optimal supply of cells with iron were selected as regulatory mutants. The mutants accumulated 6,7-dimethylpterin in high concentrations and a small amount of RF in the medium and in the cells. The activity of GTP cyclohydrolase rather than that of RF synthase increased in the mutants; the activity of RF kinase and FAD pyrophosphorylase was not elevated. Hybrids produced by crossing the regulatory mutants with wild type strains did not accumulate 6,7-dimethylpterin in the medium and the activity of the GTP cyclohydrolase did not increase; this is indicative of the negative regulation for the expression of the structural gene for GTP cyclohydrolase. The authors propose a model for the regulation of GTP cyclohydrolase and RF synthase at the gene level involving iron ions as a corepressor.     

Mechanism of the photodamage of eye structures. Changes in the lens crystalline charges after ultraviolet irradiation

UV photodamaging action on individual soluble proteins of the cattle eye crystalline lens were studied by electrofocusing. The most quantitative and qualitative changes were found in gamma-crystallines: a decrease of original polypeptide stripes and appearance of additional components in pI 5.1-6.4 region. The illumination of alpha- and beta H-crystallines resulted in qualitative changes. The appearance of aggregates with the molecular mass above 10(6)D were noticed in all the protein fractions, except beta H-crystalline.     

Function-Triggering Antibodies to the Adhesion Molecule L1 Enhance Recovery after Injury of the Adult Mouse Femoral Nerve

L1 is among the few adhesion molecules that favors repair after trauma in the adult central nervous system of vertebrates by promoting neuritogenesis and neuronal survival, among other beneficial features. In the peripheral nervous system, L1 is up-regulated in Schwann cells and regrowing axons after nerve damage, but the functional consequences of this expression remain unclear. Our previous study of L1-deficient mice in a femoral nerve injury model showed an unexpected improved functional recovery, attenuated motoneuronal cell death, and enhanced Schwann cell proliferation, being attributed to the persistent synthesis of neurotrophic factors. On the other hand, transgenic mice over-expressing L1 in neurons led to improved remyelination, but not improved functional recovery. The present study was undertaken to investigate whether the monoclonal L1 antibody 557 that triggers beneficial L1 functions in vitro would trigger these also in femoral nerve repair. We analyzed femoral nerve regeneration in C57BL/6J mice that received this antibody in a hydrogel filled conduit connecting the cut and sutured nerve before its bifurcation, leading to short-term release of antibody by diffusion. Video-based quantitative analysis of motor functions showed improved recovery when compared to mice treated with conduits containing PBS in the hydrogel scaffold, as a vehicle control. This improved recovery was associated with attenuated motoneuron loss, remyelination and improved precision of preferential motor reinnervation. We suggest that function-triggering L1 antibodies applied to the lesion site at the time of injury over a limited time period will not only be beneficial in peripheral, but also central nervous system regeneration.     

Human mitochondrial disease-like symptoms caused by a reduced tRNA aminoacylation activity in flies

The translation of genes encoded in the mitochondrial genome requires specific machinery that functions in the organelle. Among the many mutations linked to human disease that affect mitochondrial translation, several are localized to nuclear genes coding for mitochondrial aminoacyl-transfer RNA synthetases. The molecular significance of these mutations is poorly understood, but it is expected to be similar to that of the mutations affecting mitochondrial transfer RNAs. To better understand the molecular features of diseases caused by these mutations, and to improve their diagnosis and therapeutics, we have constructed a Drosophila melanogaster model disrupting the mitochondrial seryl-tRNA synthetase by RNA interference. At the molecular level, the knockdown generates a reduction in transfer RNA serylation, which correlates with the severity of the phenotype observed. The silencing compromises viability, longevity, motility and tissue development. At the cellular level, the knockdown alters mitochondrial morphology, biogenesis and function, and induces lactic acidosis and reactive oxygen species accumulation. We report that administration of antioxidant compounds has a palliative effect of some of these phenotypes. In conclusion, the fly model generated in this work reproduces typical characteristics of pathologies caused by mutations in the mitochondrial aminoacylation system, and can be useful to assess therapeutic approaches.