Two types of information processing in cercal systems of insects: directional sensitivity of giant interneurons

Summary Cercal systems of seven insect species (cricketMelanogryllus desertus, mole cricketGryllotalpa gryllotalpa, katydidsPholidoptera pustulipes andTettigonia viridissima, cockroachesPeriplaneta americana andBlatta orientalis, and locustLocusta migratoria) were examined for direction-sensitive giant interneurons (GIs) that are excited by cercal receptors but have directional preferences independent of cercus position. Such GIs are known for the cricketsAcheta domesticus andGryllus bimaculatus. Directional sensitivity diagrams (DSDs) of GIs were obtained by recording and analysing the electrical responses of abdominal connectives to sound stimuli from various directions. For each animal DSDs were plotted in the form of polar graphs for two or three positions of the stimulated cercus so that the effect of cercus position on the orientation of the DSD could be evaluated.All insects studied had GIs whose DSDs for fixed cercus positions were similar in appearance to the DSDs described for GIs of the cricketsAcheta domesticus andGryllus bimaculatus. Most of these DSDs were shaped like a figure 8 (when airflow is used as the stimulus instead of sound, each DSD has only one lobe). However, not all GIs demonstrated a constant directional preference. GIs with constant directionality were found only inMelanogryllus desertus, Pholidoptera pustulipes, Tettigonia viridissima andLocusta migratoria. In these insects DSDs from one GI plotted for different cercus positions had approximately the same orientation (Figs. 4–7). In contrast, GIs inGryllotalpa gryllotalpa, Periplaneta americana andBlatta orientalis had DSDs whose orientation changed in accordance with a change in position of the stimulated cercus (Figs. 8–10).Thus, direction-sensitive GIs investigated here can be divided into two types: (1) GIs with constant directionality (whose DSDs are fixed to the body, and (2) GIs with variable directionality (whose DSDs are fixed to the cerci). To date, in each species only GIs of the same type have been encountered. This may be an indication that cercal systems can be divided into two categories according to how they process information. However, since we have not tested all GIs in each species, we cannot rule out the possibility that a species might have both types of GIs.Abbreviations DSD directional sensitivity diagram - GI giant interneuron - TAG terminal abdominal ganglion     

Immobilization of β-glucosidase on an inorganic carrier

The enzymatic hydrolysis of cellobiose, an important intermediate of the decomposition of cellulose containing materials, with immobilized β-glucosidase preparations from Geotrichium candidum, Trichoderma lignorum and Aspergillus foetidus was examined At first it was the aim to prepare from differently purified samples with different specific cellobiase activities high active preparations on the basis of the inorganic carrier Silochrom S-80. Characteristics e.g. thermal stability and temperature and pH optimum of immobilized preparations were compared with those of soluble preparations Kinetics of cellobiose hydrolysis by immobilized enzyme preparations were studied.     

Sequential mechanism of refolding of carbonic anhydrase B

The kinetics of refolding of bovine carbonic anhydrase B was studied by a variety of methods over a wide range of times (from milliseconds to hours). It has been shown that protein refolding proceeds through three stages. At the first stage (t1/2 approximately equal to 0.03 s) hydrophobic clusters and a compact state of the chain are formed. At the second stage (t1/2 approximately equal to 140 s) hydrophobic clusters are desolvated and the rigid native-like hydrophobic core is formed. At the third stage (t1/2 approximately equal to 600 s) the native active protein is formed.     

The role of the antioxidant system in the mechanism of adaptation to intensive noise

It has been shown in the experiment with albino rats that the prolonged influence of stable noise (90 dB) results in a shift of the redox equilibrium in the thiol-disulphide and ascorbate systems of the adrenal gland and myocardium tissues towards oxidation and the activity of glucoso-6-phosphate dehydrogenase and superoxide dismutase decreases. A concept on the pathogenetic role of the redox equilibrium disturbance in the thiol-disulphide system, in particular, in the development of noise pathology is suggested.     

Search for genes influencing the maintenance of the [<Emphasis Type="Italic">ISP</Emphasis><Superscript>+</Superscript>] prion-like antisuppressor determinant in yeast with the use of an insertion gene library

The prion-like determinant [ISP ⁺] manifests itself as an antisuppressor of certain sup35 mutations. To establish that [ISP ⁺] is indeed a new yeast prion, it is necessary to identify the gene that codes for the protein whose prion form is [ISP ⁺]. Analysis of the transformants obtained by transformation of an [ISP ⁺] strain with an insertion gene library revealed three genes controlling the [ISP ⁺] maintenance: UPF1, UPF2, and SFP1. SFP1 codes for a potentially prionogenic protein, which is enriched in Asn and Gln residues, and is thereby the most likely candidate for the [ISP ⁺] structural gene. UPF1 and UPF2 code for components of nonsense-mediated mRNA decay. The [ISP ⁺] elimination caused by UPF1 and UPF2 inactivation was reversible, and Upf1p and Upf2p were not functionally related to phosphatase Ppz1p, which influences the [ISP ⁺] manifestation. Possible mechanisms sustaining the influence of UPF1 and UPF2 on [ISP ⁺] maintenance are discussed.     

Translational regulation of potato virus X RNA-coat protein complexes: the key role of a coat protein N-terminal peptide

The efficiency of in vitro translation of potato virus X (PVX) RNA within vRNP complexes assembled from genomic RNA and viral CP was examined. The vRNP particles contain the 5'-proximal RNA segments encapsidated by helically arranged CP head-like portions heterogeneous in length and the CP-free RNA tail. Translation of RNA is completely repressed upon incubation with PVX CP and is accompanied by vRNP particles production. By contrast, translation is activated in vRNPs in vitro assembled using two CP forms, differing in the principals of their N-terminal peptides modification. The N-terminal peptide of PVX CP represents the major phosphorylation site(s) for Thr/Ser-specific protein kinases. It was shown that: (i) CP phosphorylation results in a translational activation of vRNP; (ii) removal of N-terminal peptide from CP abolished activation and CP retains the translation repressing ability. It was suggested that substitution of Ser/Thr residues by non-phosphorylated Ala/Gly in N-terminal peptide of the mutant CP will led to a complete inhibition of vRNP translation. However, opposite results were obtained in our experiments: (i) RNA of such mutant virus (PVX-ST) was efficiently translated within the virions; (ii) RNA of a wild-type (wt) PVX also efficiently translated in mixedly assembled vRNP "wt PVX RNA + PVX-ST CP"; (iii) opposite result (repression of translation) was obtained with "mixed" vRNP (PVX-ST RNA + wtPVX CP). Therefore, the N-terminal peptide located at the surface of the particle and of the particles plays a key role in translation activation of the RNA encapsidated in vRNP and native virions.