Scent Marking in Female Prairie Voles: a Test of Alternative Hypotheses

We conducted three experiments with females in different stages of reproductive condition to test alternative hypotheses for the function of scent marking in female prairie voles, Microtus ochrogaster . The three reproductive categories were isolated females prior to sexual stimulation (anoestrous), sexually stimulated (oestrous) and lactating. Females in different reproductive condition were given the opportunity to scent mark clean unmarked substrate or areas that had previously been marked by adult females or adult males. The numbers of scent marks deposited by females did not differ statistically for females in different reproductive condition. However, there was a trend for anoestrous females to mark the most, oestrous females less, and lactating females the least. The lack of scent marking by lactating females might be to reduce conspicuousness to conspecifics or predators. Oestrous females tended to mark the most in the area marked previously by males, although the difference was not statistically significant.
Our results provide some support for a mate-attraction hypothesis and a territorial-defense hypothesis, but were most consistent with a self-advertisement hypothesis. Over marking was uncommon and did not differ by experiment or sex of previous donor. Our results suggest that the number and placement of scent marks by females are highly variable and function primarily to convey individual identity.     

Selenite Reduction by the Thioredoxin System: Kinetics and Identification of Protein-Bound Selenide

Selenite (SeO₃ ^2?) assimilation into a bacterial selenoprotein depends on thioredoxin (trx) reductase in Esherichia coli, but the molecular mechanism has not been elucidated. The mineral-oil overlay method made it possible to carry out anaerobic enzyme assay, which demonstrated an initial lag-phase followed by time-dependent steady NADPH consumption with a positive cooperativity toward selenite and trx. SDS-PAGE/autoradiography using ⁷⁵Se-labeled selenite as substrate revealed the formation of trx-bound selenium in the reaction mixture. The protein-bound selenium has metabolic significance in being stabilized in the divalent state, and it also produced the selenopersulfide (-S-SeH) form by the catalysis of E. coli trx reductase (TrxB).     

Facts and Hypotheses Concerning the Control of Odontoblast Differentiation

Numerous studies using amphibians have demonstrated that preodontoblasts emerging from the dental papilla are derived from cranial neural crest cells [4, 12, 46, 64]. However this has not been established for mammals. The history of odontogenesis begins during the early stages of cranial-facial development when the maxillary and mandibular processes develop. Continuous epithelio-mesenchymal interactions condition the histogenesis and morphogenesis of the teeth [24–26, 43, 44, 49, 51,58] as well as the terminal differentiation of odontoblasts and ameloblasts [23, 47, 52, 54, 59, 61, 67].
During recent years a considerable amount of experimental data relating to differentiation of odontoblasts has been published. We summarize these data and attempt to integrate them in deductive hypotheses concerning the control of odontoblast differentiation.     

Reduction of Presynaptic Action Potentials by PAD: Model and Experimental Study

A compartmental model of myelinated nerve fiber was used to show that primary afferent depolarization (PAD), as elicited by axo-axonic synapses, reduces the amplitude of propagating action potentials primarily by interfering with ionic current responsible for the spike regeneration. This reduction adds to the effect of the synaptic shunt, increases with the PAD amplitude, and occurs at significant distances from the synaptic zone. PAD transiently enhances the sodium current activation, which partly accounts for the PAD-induced fiber hyperexcitability, and enhances sodium inactivation on a slower time course, thus reducing the amplitude of action potentials. In vivo, intra-axonal recordings from the intraspinal portion of group I afferent fibers were carried out to verify that depolarizations reduced the amplitude of propagating action potentials as predicted by the model. This article suggests PAD might play a major role in presynaptic inhibition.     

Thioredoxin and Redox Control within the New Concept of Oxidative Signaling

During the last decade, plant thioredoxins (TRX) h-type have been shown to be implicated in several new roles like the protection against the oxidative stress by their ability to reduce some antioxidant proteins as peroxiredoxins (PRX) or methionine-sulphoxide-reductases (MSR). However, the concept of the oxidative stress is changing and this fact raises the question of the TRX roles in this new context. In the January issue of Plant Physiology, we have presented two TRXsh from Pisum sativum differently involved in the control of the redox status. PsTRXh1 is an h-type TRX that acts by reducing classical antioxidant proteins. PsTRXh2 seems to be also involved in redox control, however it could act contrary to its counterpart h1. Both proteins may play antagonistic roles in pea in order to lead a better control of the redox status.Key Words: abiotic stress, oxidative signalling, thioredoxins, Pisum sativum, ROSHigh concentration of reactive oxygen species (ROS) in plant cells involve the activation of different antioxidant systems which reestablish the redox status leading to better physiological conditions. On the other hand, it has been well established that at certain levels, the ROS act as second messengers in signal transduction cascades in several processes in plant cells.¹ At the light of these events, it has been proposed the reevaluation of the concept of oxidative stress towards “oxidative signalling.”² This concept involves all the cellular mechanisms that let the plant cells sense and act in response to modified environmental conditions. Several cellular systems are involved in such role, and in these last years, plant TRXs have been shown to be involved in several number of metabolic pathways linked to the regulation of the redox imbalance,³ mainly for the case of the h-type cluster of the TRXs.^4–6In our last work,⁷ we have described two pea TRXs of the h-type cluster, PsTRXh1 and PsTRXh2 that are differentially, and even antagonistically, involved in the redoxregulation control, probably through their interaction with different target proteins. We proposed that PsTRXh1 might be involved in the control of the ROS levels in pea tissues due to its ability to interact with several antioxidant proteins in vivo. It is now very well known that some members of the TRX family reduce PRX,^8–10 an antioxidant enzyme involves in the direct deactivation of some oxidant agents or the MSR,^11,14,15 in charge of the recovery of the oxidized methionine, both in a very specific manner. Due to the increase of PsTRXh1 both at gene expression and protein levels in plant heterotrophic tissues in response to the H₂O₂ treatment, and because it is also capable of conferring resistance towards hydrogen peroxide when produced in a yeast trx1Δ trx2Δ strain,¹⁶ one function of this TRX member could be the reduction in vivo of some PRX and/or MSRA counterparts in Pea tissues in the context of the oxidative signalling.Interestingly, PsTRXh2 gene and its corresponding protein showed very different behaviours to that presented by its homologous h1, reinforcing the idea that some TRX isoforms in plants are capable of functional specificity in vivo. PsTRXh2 is expressed in all tissues assays, mainly in roots, but at an extremely low level compared with that of PsTRXh1. Its divergent functional behaviour was confirmed both in Pea plantlets and yeast. In fact, contrary to PsTRXh1, PsTRXh2 provides hypersensitivity in the yeast trx1Δ trx2Δ mutant. We explained the different behaviour by suggesting that PsTRXh2 might interact with some target(s) involved either directly or indirectly in hydrogen peroxide detoxification, either by compromising the target function in resistance to the ROS or by reinforcing the target function in producing sensitivity to H₂O₂. Most probably, PsTRXh1 and PsTRXh2 interact with very different partners, and the characterization of such targets may help in the deciphering of PsTRX isoforms. As short-term future experiments, using the TRX-specific two-hybrid system that was published recently,⁸ comparative efficiencies of PsTRX isoforms could be performed to reduce some putative target involved in H₂O₂ detoxification, including PsTRXh3 and PsTRXh4.¹⁷ Unravelling Pea TRX interactome should help in deciphering the function of each isoform.However, we have also considered the possibility that PsTRXh2 could interact with the same target that PsTRXh1, but producing an opposite effect. In the yeast context, the protein targeted by the heterologous plant TRXs responsible of this complementation is a type-II PRX.⁵ We think that PsTRXh2 could interact with this yeast PRX blocking it and producing the hypersensitivity. In fact, we have found a similar effect in other protein targeted in vitro by TRXs. In the (Fig. 1), we present the in vitro ability of PsTRXh1 and PsTRXh2 to reduce and activate the pea chloroplastic fructose-1,6-bisphosphatase (FBPase). In the presence of PsTRXh1, FBPase presents TRX-dependent activity but lower than that found when chloroplastic f and m1 isoforms are used.¹² On the opposite, PsTRXh2 presents no only FBPase activation capability but its presence induces the FBPase inhibition, as the enzymatic activity was lower than that exhibited by this enzyme without TRX.Open in a separate windowFigure 1TRX-dependent chloroplastic FBPase activity two-step procedure.¹³ , PsTRXf; ▴, PsTRXm1; •, PsTRXh1; , PsTRXh2. The negative control (no TRX) is represented by a symbol-less line. Numbers in each line represent maximum enzymatic velocity as OD₃₄₀/min.Considering all data, we think that the behaviour showed by both pea h-type TRXs is due to their interactions with several protein-targets, as the PRXs: when the ROS levels increase drastically, cells develop high redox imbalances or even undergo oxidative stress. In this situation, all antioxidant mechanisms must be activated, including the increase of PsTRXh1 expression and protein quantities, giving rise to a more efficient cell detoxification. Under nonimbalance conditions of the redox status, PsTRXh2 could act by interacting (activating or inhibiting) with some protein targets. However, the physiological target for PsTRXh2 are not yet described nor supposed. Our results suggest that its role in the redox control is by producing sensitivity to oxidant agents, maybe by allowing physiological ROS levels in cells.     

Reduction Potentials of Imine-Substituted, Biologically Active Pyridines: Possible Relation To Activity

Cyclic voltammetry data were obtained for a number of biologically active compounds which incorporate imine substitution on the pyridine nucleus. The reductions in acid (iminium ion formation) were for the most part reversible, and in the range of—0.5 to—0.7 V. The toxic effect of these drugs is thought to be caused by the generation of reactive oxygen radicals that arise viacharge transfer, or by disruption of electron transport chains.     

Dissimilatory Selenate Reduction Potentials in a Diversity of Sediment Types

We measured potential rates of bacterial dissimilatory reduction of ⁷⁵SeO₄²⁻ to ⁷⁵Se⁰ in a diversity of sediment types, with salinities ranging from freshwater (salinity = 1 g/liter) to hypersaline (salinity = 320 g/liter and with pH values ranging from 7.1 to 9.8. Significant biological selenate reduction occurred in all samples with salinities from 1 to 250 g/liter but not in samples with a salinity of 320 g/liter. Potential selenate reduction rates (25 nmol of SeO₄²⁻ per ml of sediment added with isotope) ranged from 0.07 to 22 μmol of SeO₄²⁻ reduced liter⁻¹ h⁻¹. Activity followed Michaelis-Menten kinetics in relation to SeO₄²⁻ concentration (K_m of selenate = 7.9 to 720 μM). There was no linear correlation between potential rates of SeO₄²⁻ reduction and salinity, pH, concentrations of total Se, porosity, or organic carbon in the sediments. However, potential selenate reduction was correlated with apparent K_m for selenate and with potential rates of denitrification (r = 0.92 and 0.81, respectively). NO₃⁻, NO₂⁻, MoO₄²⁻, and WO₄²⁻ inhibited selenate reduction activity to different extents in sediments from both Hunter Drain and Massie Slough, Nev. Sulfate partially inhibited activity in sediment from freshwater (salinity = 1 g/liter) Massie Slough samples but not from the saline (salinity = 60 g/liter) Hunter Drain samples. We conclude that dissimilatory selenate reduction in sediments is widespread in nature. In addition, in situ selenate reduction is a first-order reaction, because the ambient concentrations of selenium oxyanions in the sediments were orders of magnitude less than their K_ms.     

Web-Based Computational Chemistry Education with CHARMMing III: Reduction Potentials of Electron Transfer Proteins

A module for fast determination of reduction potentials, E°, of redox-active proteins has been implemented in the CHARMM INterface and Graphics (CHARMMing) web portal (www.charmming.org). The free energy of reduction, which is proportional to E°, is composed of an intrinsic contribution due to the redox site and an environmental contribution due to the protein and solvent. Here, the intrinsic contribution is selected from a library of pre-calculated density functional theory values for each type of redox site and redox couple, while the environmental contribution is calculated from a crystal structure of the protein using Poisson-Boltzmann continuum electrostatics. An accompanying lesson demonstrates a calculation of E°. In this lesson, an ionizable residue in a [4Fe-4S]-protein that causes a pH-dependent E° is identified, and the E° of a mutant that would test the identification is predicted. This demonstration is valuable to both computational chemistry students and researchers interested in predicting sequence determinants of E° for mutagenesis.