Is neurotensin in the brain involved in thermoregulation of the monkey?

Cannulae for intracerebroventricular (ICV) infusion were implanted stereotaxically in monkeys (Macaca fasicularis) maintained post-operatively in a primate restraint chair. During each experiment, a series of physiological measures was recorded simultaneously on a polygraph which included colonic temperature, vasomotor tone, heart rate, respiratory rate, and basal metabolism as reflected by O₂ uptake. The ICV infusion in a volume of 0.5 ml of neurotensin (NT) in doses ranging from 3–150 μg produced neither a statistically significant nor consistent change in body temperature or vasomotor response. Although the highest dose of 450 μg NT infused ICV caused an immediate bradycardia and a concomitant decline in metabolic and respiratory rates, an average decline in core temperature of 0.6°C and the accompanying cutaneous vasodilation often had a latency as long as 1.0 hr. In contrast to the typical hypothermia in this species following an ICV infusion of catecholamines, implicated in the central pathways underlying thermoregulation, NT failed to elicit a coordinated set of physiological responses for heat dissipation in the monkey. Therefore, it is unlikely that this tridecapeptide plays a role in the central mechanisms mediating the control of body temperature of this primate species.     

Is mucus involved in biocrystallization?

Summary Freeze-dried intestinal mucus of sea-water-adapted eels was analysed by scanning electron microscopy (SEM) and X-ray microanalysis. Calcite crystals were observed in the mucus fibres; their concentration increased along the hindgut. Random SEM observations made in situ indicated that mucus fibres were involved in the genesis of these crystals. Calcium-rich mucus globules were found fused inside crystal matrices. Single typical rhombohedric crystals of various complexity appeared within the mucus framework. The steps of crystal biogenesis were reconstituted in in-vitro conditions.     

Rho/Rho-dependent kinase affects locomotion and actin–myosin II activity of Amoeba proteus

Summary. The highly motile free-living unicellular organism Amoeba proteus has been widely used as a model to study cell motility. However, the molecular mechanisms underlying its unique locomotion are still scarcely known. Recently, we have shown that blocking the amoebaes endogenous Rac- and Rho-like proteins led to distinct and irreversible changes in the appearance of these large migrating cells as well as to a significant inhibition of their locomotion. In order to elucidate the mechanism of the Rho pathway, we tested the effects of blocking the endogenous Rho-dependent kinase (ROCK) by anti-ROCK antibodies and Y-27632, (+)-(R)-trans-4-(1-aminoethyl)-N-(4-pyridyl)cyclohexanecarboxamide dihydrochloride, a specific inhibitor of ROCK, on migrating amoebae and the effect of the Rho and ROCK inhibition on the actin-activated Mg-ATPase of the cytosolic fraction of the amoebae. Amoebae microinjected with anti-ROCK inhibitors remained contracted and strongly attached to the glass surface and exhibited an atypical locomotion. Despite protruding many pseudopodia that were advancing in various directions, the amoebae could not effectively move. Immunofluorescence studies showed that ROCK-like protein was dispersed throughout the cytoplasm and was also found in the regions of actin–myosin II interaction during both isotonic and isometric contraction. The Mg-ATPase activity was about two- to threefold enhanced, indicating that blocking the Rho/Rho-dependent kinase activated myosin. It is possible then that in contrast to the vertebrate cells, the inactivation of Rho/Rho-dependent kinase in amoebae leads to the activation of myosin II and to the observed hypercontracted cells which cannot exert effective locomotion.Correspondence and reprints: Department of Muscle Biochemistry, Nencki Institute of Experimental Biology, 3 Pasteur ulica, 02-093 Warsaw, Poland.     

Is the renin-angiotensin system involved in urinary concentration mechanisms?

Renin release elicited by i.v. injection of loop-diuretics was used to study the effects of angiotensin II (AII) on intrarenal hemodynamics. The vasoconstrictive action of intrarenally synthesized AII predominates in the efferent glomerular arteriole. Such a vasoconstrictive effect could affect blood flow in the vasa recta which stem from efferent arterioles of juxtamedullary glomeruli. Renin secretion and renal inner medullary blood flow (tissue clearance of 133Xe) were simultaneously measured before and after frusemide-induced renin release. The relationship between renin secretion and renal inner medullary blood flow was inverse. Changes in renal medullary blood flow may be physiological determinants of medullary osmolality and renal concentration ability. The intrarenal role of AII in urinary concentration recovery after frusemide was examined. Inhibition of renin release by propranolol or AII-blockade (by saralasin or Hoe 409) delayed recovery of urinary osmolality. In the conscious rat, propranolol slowed down recovery of the cortico-papillary gradient for sodium. Its vasoconstrictive action on the efferent glomerular arteriole might enable the renin-angiotensin system to participate in the control of renal excretion of salt and water.     

Is astrocyte laminin involved in axon guidance in the mammalian CNS?

This paper provides evidence for the expression of laminin on glia in correlation with axon elongation and nerve pathway formation during embryonic development of the mouse optic nerve and other parts of the central nervous system (CNS). We show that punctate deposits of laminin on immature glial cells precede the entrance of the first optic axons into the nerve, and remain in close association with growing axons. Furthermore, we show that in one particular region of the optic pathway that the retinal ganglion cell axons avoid in normal animals (i.e., the pigmented area of the distal nerve) the punctate laminin matrix is missing. As the optic nerve matures punctate laminin deposits disappear, and laminin is reduced in the astroglial cytoplasm. The close correlation of the punctate form of laminin with early axonal growth is true not only in the optic nerve but also in some other parts of the CNS. We demonstrate such punctate laminin deposits in a model of astrocyte-induced regeneration of the corpus callosum in acallosal mice (G. Smith, R. Miller, and J. Silver, 1986, J. Comp. Neurol. 251, 23-43), and in glia associated with several normal developing axon trajectories, such as the corpus callosum, fornix, and pathways in the embryonic hindbrain. In all of these regions punctate laminin deposits are found on astroglia that are associated with early growing axons. Our results indicate that the punctate form of laminin, produced by astrocytes, may be an important factor involved in axon elongation and nerve pathway formation in the mammalian CNS.     

Is peroxidase involved in ethylene biosynthesis?

Wheat (Triticum aestivum L. cv. Jubilar) coleoptile segments convert 1-aminocyclopropane-1-carboxylic acid (ACC) to ethylene. This process is totally inhibited by nitrogen atmosphere and severely inhibited by free radical scavengers (sodium benzoate, ferulic acid), inhibitors of reactive -SH groups ( p -chlormercuribenzoate, iodoacetate), CoCl₂ and EDTA. Indole-3-acetic acid, aminoethoxyvinyl glycine, cycloheximide, actinomycin D, pyridoxal phosphate and NADH have no effect on ACC conversion to ethylene. Some in vivo characteristics of this conversion suggest that it could be catalyzed by peroxidase. However, isoperoxidase B1 isolated from wheat seedlings was not able to catalyze in vitro conversion of ACC to ethylene under a wide range of reaction conditions. Therefore, it is concluded that peroxidase is not directly involved in ethylene biosynthesis.     

Is cholinergic activity of the caudate nucleus involved in memory?

A review was made of experiments dealing with the involvement of cholinergic activity of the caudate nucleus in memory processes. Injections of acetylcholine-receptor blockers or of neurotoxins against cholinergic interneurons into the striatum produce marked impairments in acquisition and retention of instrumental tasks while injections of acetylcholine or choline into the caudate produce the opposite effect. However, after a period of overtraining cholinergic blockade or interference with neural activity of the caudate does not produce significant deficits in retention. It is concluded that striatal cholinergic activity is critically involved in memory of recent events and that long-term memory is mediated by different neurochemical systems outside the caudate nucleus.     

Is the cytoskeleton-plasma membrane complex involved in lens protein biosynthesis?

Calf lens fiber cells contain a population of polyribosomes that direct, at leastin vitro, the synthesis of a specific plasma membrane protein MP26. This protein may serve as a marker in terminal differentiation, since it is absent in the lens epithelium but appears in lens fiber plasma membranes. The MP26 manufacturing polyribosomes are found to be associated with a structural complex in which also the cytoskeleton and plasma membranes participate. They can be released from the complex by treatment with DNAse I. This result presumably reflects the involvement of actin in the linkage of the MP26 synthesizing polyribosomes to the cytoskeleton-membrane complex.     

Is cyclic AMP involved in the defibrillating effect of sotalol ?

Ventricular fibrillation induced in animals pretreated with sotalol, a class III antiarrhythmic agent, would spontaneously terminate and revert into a sinus rhythm. This phenomenon has been atributed to the class III action of this Drug, I.e., prolongation of myocardial action potential duration and effective refractory period. Since various observations suggested that these alone cannot explain the defibrillating phenomenon, we hypothesised that sotalol affeced ventricular intercellular synchronization by increasing intercellular coupling. Our recent experimental studies have shown that sotalol antagonized the cellular decoupling to guinea pig ventricular muscle strip caused by perfusion with either a hypoxic normal Tyrode's solution or an oxygenated high Ca2+ Tyrode's solution. We assumed that the most likely mechanism for the restoration of intercellular coupling would be by increasing intracellular cAMP concentration. In order to test this hypothesis, we studied the modification of this sotalol-induced recoupling by a cAMP dependent protein kinase inhibitor. The results clearly supported our assumption since the addition of Arg-Gly-Tyr-Ala-Leu-Gly (pure A- kinase inhibitor) prevented the aforementioned cellular recoupling action of sotalol in a dose-dependent manner. It can thus be concluded that changes in intracellular cAMP level are involved in the synchronizing /defibrillating effect of sotalol.     

Is the Rsp5 ubiquitin ligase involved in the regulation of ribophagy?

Under nutrient limiting conditions, cytoplasmic components are randomly sequestered into double-membrane vesicles called autophagosomes and delivered to the lysosome/vacuole for degradation and recycling. In the last few years, however, it has been observed that several cytoplasmic components such as organelles, pathogens or specific protein complexes can also be selectively targeted for degradation by autophagy-related pathways (reviewed in ref. 1). We have recently shown that in S. cerevisiae, mature ribosomes are subject to such selective degradation by autophagy under starvation conditions, in a process that we termed 'ribophagy.'(2) By genetic screening, we found that selective degradation of 60S large ribosomal subunits depends on the ubiquitin protease Ubp3 and its cofactor Bre5, implying that ribophagy is regulated by ubiquitin-dependent steps. Interestingly, several ubiquitinated proteins accumulate in ribosome fractions isolated from ubp3Delta cells, suggesting that the regulation of ribophagy by ubiquitin may be direct. Here we present data on a potential role of the ubiquitin ligase Rsp5 as a positive regulator of ribophagy, and discuss the possible involvement of ubiquitin as a signaling molecule in this process.     

Is a ferroxidase involved in the high-affinity iron uptake in Chlamydomonas reinhardtii?

In phosphorus deficient soils and under smallscale farming systems, the development of efficient management strategies for P fertilizers is crucial to sustain food production. A field experiment was conducted on a P-fixing Acrisol in western Kenya to study possibilities of replenishing soil P with seasonal additions of small rates of P fertilizers. Triple superphosphate was applied at 0, 10, 25, 50 and 150 kg P ha^–1 for 5 consecutive maize growing seasons followed by 4 seasons of residual crops. Maize yields and soil P fractions were determined. Although maize responded to additions of 10 kg P ha^–1 with a cumulative grain yield of 16.8 Mg ha^–1, at the end of the experiment, compared to 8.8 Mg ha^–1 in the non-P fertilized plots, soil labile P did not increase correspondingly. Seasonal additions of 150 kg P ha^–1 increased maize yields to a cumulative value of 39 Mg ha^–1 at the end of the experiment, and increased all soil inorganic P fractions. At the third season of residual phase, treatment with a cumulative addition of 750 kg P ha^–1 gave the highest yields compared to treatments in the same residual stage, but these yields were considered less than the maximum yield of the season. This indicates that the large build up of soil P was not available for crop uptake. The inorganic P fraction extracted by NaHCO₃ was the most affected by changes in management, increasing during the input phase and decreasing after interruption of P addition, for all P rates. The decrease in this pool during the residual phase could be explained by the maize uptake. This study showed that seasonal additions of 25 kg P ha^–1 can increase maize yield with gradual replenishment of soil P.     

Is the Rsp5 ubiquitin ligase involved in the regulation of ribophagy?

Under nutrient limiting conditions, cytoplasmic components are randomly sequestered into double-membrane vesicles called autophagosomes and delivered to the lysosome/vacuole for degradation and recycling. In the last few years, however, it has been observed that several cytoplasmic components such as organelles, pathogens or specific protein complexes can also be selectively targeted for degradation by autophagy-related pathways (reviewed in reference 1). We have recently shown that in S. cerevisiae, mature ribosomes are subject to such selective degradation by autophagy under starvation conditions, in a process that we termed ‘ribophagy’.² By genetic screening, we found that selective degradation of 60S large ribosomal subunits depends on the ubiquitin protease Ubp3 and its cofactor Bre5, implying that ribophagy is regulated by ubiquitin-dependent steps. Interestingly, several ubiquitinated proteins accumulate in ribosome fractions isolated from ubp3? cells, suggesting that the regulation of ribophagy by ubiquitin may be direct. Here we present data on a potential role of the ubiquitin ligase Rsp5 as a positive regulator of ribophagy, and discuss the possible involvement of ubiquitin as a signaling molecule in this process.

Addendum to: Kraft C, Deplazes A, Sohrmann M, Peter M. Mature ribosomes are selectively degraded upon starvation by an autophagy pathway requiring the Ubp3p/Bre5p ubiquitin protease. Nat Cell Biol 2008; 10:602-10.     

Is the nuclear matrix the site of DNA replication in eukaryotic cells?

Four types of experiment were carried out to test the recently proposed model of matrix-bound replication in eukaryotic cells. In experiments with pulse-labelling we found preferential association of newly replicated DNA with the matrix only when the procedure for isolation includes first high-salt treatment of isolated nuclei and then digestion with nucleases, or when prior to digestion the nuclei have been stored for a prolonged time. In both cases, however, evidence was found that this preferential association is due to a secondary, artifactual binding of the newly replicated chromatin region to the matrix elements. Pulse-chase experiments and experiments with continuous labelling were carried out to answer the question whether during replication the DNA is reeled through the replication complexes, i.e., whether newly replicated DNA is temporarily or permanently associated with the matrix. The results showed that at that time the matrix DNA does not move from its site of attachment. Since, according to the model of matrix-bound replication, the forks are assumed to be firmly anchored to high-salt resistant proteinaceous matrix structures, the chromatin fragments isolated with endonuclease not recognizing newly replicated DNA and purified by sucrose gradient centrifugation should be free of replication intermediates. The electronmicroscopic analysis of such fragments revealed the existence of intact replication micro-bubbles. Moreover, the fragments with replication configurations appeared as smooth chromatin fibres not attached to elements characteristic for the matrix. All these experiments suggest that the nuclear skeleton is not a native site of DNA replication in eukaryotic cells.     

Is the COI barcoding gene involved in speciation through intergenomic conflict?

We here test the proposition that changes in the barcoding region of COI are commonly involved in speciation through intergenomic conflict. We demonstrate that this is unlikely given that even with incomplete taxon sampling, 78-90% of closely-related animal species have identical COI amino acid sequences. In addition, in those cases where amino acid substitutions between closely related species are observed, the inter- and intra-specific substitution patterns are very similar and/or lack consistent differences in the number, position and type of amino acid change. Overall, we conclude that there is little evidence for a widespread involvement of the barcoding gene in speciation.     

Is light quality involved in the regulation of the photosynthetic apparatus in attached rice leaves?

The regulatory effect of light quality on the photosynthetic apparatus in attached leaves of rice plants was investigated by keeping rice plants under natural light, in complete darkness, or under illumination with light of different colors. When leaves were left in darkness and far-red (FR)-light conditions for 6 days at 30°C, there was an initial lag in chlorophyll (Chl) content, Chl a/b ratio, and maximum photosystem (PS) II photochemistry that lasted until the second day; these then rapidly decreased on the fourth day. In contrast, ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) rapidly disappeared with no lag under low or zero light conditions. By using spectrophotometric quantitation, it was determined that the PSII and PSI reaction centers were regulated by light quality, but cytochrome (Cyt) f was regulated by light intensity. However, the PSII heterogeneity was also strongly modified by the light intensity; PSIIα with the large antenna decreased markedly both in content and in antenna size. Consequently, the PSIIα/PSI ratio declined under FR-light because the low intensity of FR-light dominated over its quality in the modulation of the PSIIα/PSI ratio. An imbalance between them induced the generation of reactive oxygen species (ROS), although the ROS were scavenged by stromal enzymes such as superoxide dismutase (SOD), ascorbate peroxidase (APX), and glutathione reductase (GR). The activities of these stromal enzymes are also regulated by light quality. Thus, although the photosynthetic apparatus is regulated differently depending on light quality, light quality may play an important role in the regulation of the photosynthetic apparatus.