Optimal average path of the instantaneous helical axis in planar motions with one functional degree of freedom

This paper presents a model for determining the path of the instantaneous helical axis (IHA) that optimally represents human planar motions with one functional degree of freedom (fDOF). A human movement is said to have one fDOF when all degrees of freedom (DOFs) are coordinated such that all the kinematic variables can be expressed, across movement repetitions, as functions of only one independent DOF, except for a small natural intercycle variability quantified as lower than a prespecified value. The concept of fDOF allows taking into account that, due to motor coordination, human movements are executed in a repeatable manner. Our method uses the measurement of several repetitions of a given movement to obtain the optimal average IHA path. The starting point is a change of variables, from time to a joint position magnitude (generally an angle). In this way, instead of operating with the time-dependent single-valued trajectory of the successive cycles, our model permits the representation of any motion variable (e.g. positions and their time derivatives) as a cloud of points dependent on the joint angle. This allows the averaging to be performed over the displacements and their derivatives before determining the mean IHA path. We thus avoid the nonlinear magnification of errors and variability inherent in the IHA computation. Moreover, the IHA path can be considered as a geometric attribute of the joint and the type of motion, rather than of each single movement execution. An experiment was performed that show the accuracy and usefulness of the method.     

Molecular epidemiology of HIV-1 clades in Southern Brazil

Human immunodeficiency virus (HIV) clades B and C account for more than 60% of the HIV-1 infections worldwide. In this paper, we describe the profiles of patients infected with subtypes of HIV-1 from the state of Paraná, Southern Brazil, and correlate them with demographic and epidemiological findings. A retrospective analysis of HIV cases reported from 1999-2007 was also performed. Data from 293 patients were reviewed and 245 were older than 13 (58% female). The distribution of clades was as follows: B 140 (57%), C 67 (23%), F 24 (10%) and mosaic or unique recombinant forms (URFs) 24 (10%). Of the 48 patients younger than 13 years of age (62.5% male), vertical transmission occurred in 46 and the distribution of clades was as follows: B 14 (29%), C 24 (50%), F 7 (15%) and URFs 6 (13%). There was no significant difference in mortality between HIV-1 subtypes. In both groups, patients infected with clade C tended to have higher rates of injection drug use exposure risk.     

Effects of diterpenes from latex of Euphorbia lactea and Euphorbia laurifolia on human immunodeficiency virus type 1 reactivation

The persistence of latent HIV-infected cellular reservoirs represents the major hurdle to virus eradication in patients treated with highly active antiretroviral therapy, referred to as HAART. HIV-1 reservoirs are long-lived resting CD4⁺ memory cells containing the virus latently integrated. Since the HIV-1 reservoirs are not targeted by HAART, reactivation therapy has been suggested to purge viral latency. Bioassay-guided study of an ethyl acetate extract of Euphorbia laurifolia afforded two isomeric diterpenes that showed differential activity over HIV-1 reactivation. A previously reported compound was isolated too from Euphorbia lactea. This compound showed a potent HIV-1 reactivating effect. Bioassays results showed that HIV-1 reactivation activity is influenced by distinct structural characteristics.     

Microgravity environment uncouples cell growth and cell proliferation in root meristematic cells: The mediator role of auxin

Experiments performed in space have evidenced that, in root meristematic cells, the absence of gravity results in the uncoupling of cell growth and cell proliferation, two essential cellular functions that support plant growth and development, which are strictly coordinated under normal ground gravity conditions. In space, cell proliferation appears enhanced whereas cell growth is depleted. Since coordination of cell growth and proliferation is a major feature of meristematic cells, the observed uncoupling is a serious stress condition for these cells producing important alterations in the developmental pattern of the plant. Auxin plays a major role in these processes both by assuring the coupling of cell growth and proliferation under normal conditions and by exerting a decisive influence in the uncoupling under altered gravity conditions. Auxin is a mediator of the transduction of the gravitropic signal and its distribution in the root is altered subsequent to a change in the gravity conditions. This altered distribution may produce changes in the expression of specific growth coordinators leading to the alteration of cell cycle and protein synthesis. Therefore, available data indicate that the effects of altered gravity on cell growth and proliferation are the consequence of the transduction of the gravitropic signal perceived by columella cells, in the root tip.Key words: cell cycle, ribosome biogenesis, nucleolus, auxin efflux, graviperception, space flight, arabidopsisThe size and morphology of plants and of plant organs is basically determined by cellular activities that occur in meristems. The primary meristems are root and shoot apical meristems, located at both upper and lower ends of the plant, which are constituted by stem cells. Cell division in these meristems is required to supply new cells for expansion and differentiation of tissues and initiation of new organs, providing the basic structure of the plant body.¹ In turn, active protein synthesis is required after mitosis in order to promote the necessary cell growth, up to duplication of cell size, which will make possible a new cell division. This continuous activity of growth and proliferation in meristematic cells is controlled by auxin, whose distribution in roots sets up distinct zones for cell division, cell expansion and differentiation and determines the balance between them.^2,3Therefore, cell growth and proliferation are essential functions for plant development and they are involved in the developmental response to environmental stimuli, such as tropisms and defense mechanisms against both biotic and abiotic agents.^4–6 Gravity is a fundamental environmental condition, constant in the Earth as a factor conditioning life throughout its whole history. Plants are particularly affected by gravity in their growth, which is directed by the gravity vector producing the well known process of gravitropism.An experiment aimed to know the effects of a weightless environment on cell proliferation and growth in root meristematic cells was performed in the International Space Station. It consisted of germinating seeds of Arabidopsis thaliana in space and then growing seedlings for four days at the constant temperature of 22°C, in the darkness. Seedlings were fixed when still in space and recovered on ground to be processed for microscopical study. In addition, samples from a previous space experiment, grown in a similar way but fixed differently and including a control flight experiment in a 1 g centrifuge, were also incorporated to the analysis.^7,8 This analysis consisted of biometrical estimations of the seedling and root length, quantitative measurements at the cellular level, including number of cells per millimeter in specific cell files, in order to get an estimate of the cell proliferation rate, and morphometrical, ultrastructural and immunocytochemical study of the nucleolus, in order to know the rate of ribosome biogenesis, as an estimation of the level of protein synthesis, which is the cellular process which determines cell growth in the root meristem. Data obtained from space-flown samples were compared with 1 g ground controls and also with data from samples grown in the same conditions in a device called “Random Positioning Machine”, an efficient simulator of microgravity, which induces constant changes of the gravity vector as it is sensed by living samples.⁹ The results interestingly showed an enhanced rate of cell proliferation accompanied by a reduction of ribosome biogenesis per cell in samples grown in both real and simulated microgravity, compared to 1 g controls, either in flight or on ground.¹⁰ This alteration of essential cellular processes may go far beyond the mere change in specific physiological activities of a particular cell type, since, on the one hand, alteration of cell growth and proliferation in the root meristem may have consequences at the level of development and shaping of the whole plant; on the other hand, regulation of these cellular activities by auxin may put in connection these cellular alterations with the transduction cascade of the gravitropic signal perceived by columella cells in the root tip, which is altered when the environmental gravity conditions change and which finally results in the modification of the levels and distribution of auxin throughout the root.     

Involvement of mitogen-activated protein kinases in the symbiosis Bradyrhizobium-Lupinus

In plants, mitogen-activated protein kinases (MAPKs) are involved in signalling to hormones, cell cycle regulation, stresses, and plant defence responses. In this work, several MAPKs were detected by immunobloting in roots and nodules of Lupinus albus produced by inoculation with Bradyrhizobium sp. (Lupinus). In vitro kinase assays showed that inoculation of seedling roots with B. sp. (Lupinus) activates salt stress-inducible and stress-activated MAPKs after 5 min of incubation. By contrast, inoculation with dead B. sp. (Lupinus) or the heterologous bacteria Sinorhizobium meliloti did not induce salt stress-inducible and stress-activated MAPK activities. In vivo experiments showed that inoculation with B. sp. (Lupinus) induced the activation of MAPKs in roots. The maximal activation was in the region of the root tip with emerging hairs, which corresponds to the infection zone. The p38 MAPK inhibitors SB 202190 and SB 203580 blocked these kinase activities. Experiments with SB 202190 and the MAPKK inhibitor UO 126 altered the pattern of nodulation in the main root, decreasing the number and weight of nodules produced in the upper sites while increasing the nodule number in the younger lower root zone. These data suggest that MAPK inhibition blocks early events in the susceptible root zone to rhizobial infection, delaying nodulation, and support a role for MAPKs in the infection and nodulation of L. albus by B. sp. (Lupinus).