Novel interaction between the M4 muscarinic acetylcholine receptor and elongation factor 1A2

The activation of the muscarinic acetylcholine receptor (mAChR) family, consisting of five subtypes (M1-M5), produces a variety of physiological effects throughout the central nervous system. However, the role of each individual subtype remains poorly understood. To further elucidate signal transduction pathways for specific subtypes, we used the most divergent portion of the subtypes, the intracellular third (i3) loop, as bait to identify interacting proteins. Using a brain pull-down assay, we identify elongation factor 1A2 (eEF1A2) as a specific binding partner to the i3 loop of M4, and not to M1 or M2. In addition, we demonstrate a direct interaction between these proteins. In the rat striatum, the M4 mAChR colocalizes with eEF1A2 in the soma and neuropil. In PC12 cells, endogenous eEF1A2 co-immunoprecipitates with the endogenous M4 mAChR, but not with the endogenous M1 mAChR. In our in vitro model, M4 dramatically accelerates nucleotide exchange of eEF1A2, a GTP-binding protein. This indicates the M4 mAChR is a guanine exchange factor for eEF1A2. eEF1A2 is an essential GTP-binding protein for protein synthesis. Thus, our data suggest a novel role for M4 in the regulation of protein synthesis through its interaction with eEF1A2.     

Hermaphroditism as a reproductive strategy for metazoans; some correlated benefits

Abstract

The concept of hermaphroditism is examined, the terminology is reviewed, and several new terms are proposed: EUHERMAPHRODITISM for the occurrence together of eggs and sperm in the individual that produced them; TEMPORARY HERMAPHRODITISM for the few instances where euhermaphroditism is a brief transitional phase between sexes in protandry and protogyny, and opsiautogamy to designate the condition where sperm saved from an early male phase are used to fertilise eggs produced in a later female phase. An animal that functions successively in the different sex roles is considered to be quite distinct from one that functions as both male and female simultaneously. Further, the circumstances in which these different sexual modes are appropriate and the advantages that accrue from them are quite different. For this reason protandry, protogyny, and consecutive sexuality are not considered to be part of hermaphroditism, but rather aspects of labile gonochorism.

A major idea advanced in this paper is that hermaphroditism is of primary importance as a reproductive strategy of very small metazoans. In such animals, whose eggs are so disproportionately large that very few can be produced, hermaphroditism ensures that through having the maximal number of females the maximal number of eggs are produced and fertilised economically. For very small hermaphrodites the mate-finding difficulties associated with small size and limited motility are reduced by converting each meeting into a potential mating. Further, in hermaphroditism not only is the frequency of mating maximised. but through sperm storage the effects of matings last for a long time. and through multiple reciprocal copulations genetically diverse progenies are produced. The effective size of the gene pool is maximised, and the risk of genetic drift in sex ratio in small populations is avoided. Very small animals do not have the energetic resources to produce large numbers of large, yolky eggs, nor do they have the space in which to store them before release. Thus tiny hermaphrodites tend to produce a few eggs at a time, but over extended or continuous breeding seasons. The effects of their reduced fecundity may be further offset by precise methods of fertilisation, brooding, and commonly the suppression of pelagic phases, thus minimising losses from larval predation and overdispersal.

It is also argued that hermaphroditism may have been advantageous because of features often associated with it. Copulation with protected sperm transfer may have been especially important, not only because of economies in gamete production and use, but also in the exploitation of new habitats. In freshwater hermanhrodites copulatory or spermatophore exchange habits protect sperm from osmotic death: in endoparasites copulation protects sperm from digestive enzymes and osmotic stress in the host’s gut, and from antibodies and phagocytosis in the bloodstream.     

Farming,fishing, and fire in the history of the upper Río Negro region of Venezuela

Studies of Río Negro subsistence farming and fishing activities are used to estimate the human carrying capacity for the region and the likely pattern of human land-use during prehistory. Ceramic evidence suggests human presence in the region more than 3000 years ago. Traditional farming is labor intensive and relatively unproductive. Nevertheless, farmers achieve an energy return of 15.21, and produce 2600 kcal per work hour. Fish are the major protein source, but fish catch per unit of effort and fish yield per hectare of floodplain are very low; fishermen are probably exploiting local fish resources very close to their limit. The low human population density would suggest that the Río Negro forest has been relatively undisturbed. Nevertheless, charcoal is widespread and abundant in forest soils. This charcoal is probably from anthropogenic or natural wildfires. These results suggest a much more complex history for Amazonia than previously thought.K. Clark is a free-lance biologist residing in Lima, Peru     

Abundant Intracellular IgG in Enterocytes and Endoderm Lacking FcRn

FcRn, a non-classical MHCI molecule, transports IgG from mother to young and regulates the rate of IgG degradation throughout life. Brambell proposed a mechanism that unified these two functions, saying that IgG was pinocytosed nonspecifically by the cell into an FcRn-expressing endosome, where, at low pH, it bound to FcRn and was exocytosed. This theory was immediately challenged by claims that FcRn specificity for ligand could be conferred at the cell surface in neonatal jejunum. Assessing Brambell''s hypothesis we found abundant nonspecifically endocytosed IgG present in the cytoplasm of FcRn^−/− enterocytes. Further, IgG was present in the intercellular clefts and the cores of FcRn^+/+ but not FcRn^−/− jejunum. FcRn specificity for ligand could be determined within the cell.     

MEKK4 sequesters RIP2 to dictate NOD2 signal specificity

The Crohn's-disease-susceptibility protein, NOD2, coordinates signaling responses upon intracellular exposure to bacteria. Although NOD2 is known to activate NFkappaB, little is known about the molecular mechanisms by which NOD2 coordinates functionally separate signaling pathways such as NFkappaB, JNK, and p38 to regulate cytokine responses. Given that one of the characteristics of Crohn's disease is an altered cytokine response to normal bacterial flora, the coupling of signaling pathways could be important for Crohn's-disease pathophysiology. We find that a MAP3K, MEKK4, binds to RIP2 to sequester RIP2 from the NOD2 signaling pathway. This MEKK4:RIP2 complex dissociates upon exposure to the NOD2 agonist, MDP, allowing NOD2 to bind to RIP2 and activate NFkappaB. MEKK4 thus sequesters RIP2 to inhibit the NOD2:RIP2 complex from activating NFkappaB signaling pathways, and Crohn's-disease-associated NOD2 polymorphisms cannot compete with MEKK4 for RIP2 binding. Lastly, we find that MEKK4 helps dictate signal specificity downstream of NOD2 activation as knockdown of MEKK4 in macrophages exposed to MDP causes increased NFkappaB activity, absent p38 activity, and hyporesponsiveness to TLR2 and TLR4 agonists. These biochemical findings suggest that basal inhibition of the NOD2-driven NFkappaB pathway by MEKK4 could be important in the pathogenesis of Crohn's disease.     

Seasonal occurrence of Campylobacter spp. in surface waters and their correlation with standard indicator bacteria

Campylobacter jejuni, Campylobacter coli, and a Campylobacter-like organism were isolated from a number of natural water sources in central Washington, including ponds, lakes, and small mountain streams at elevations ranging from 1,460 to 5,400 feet (ca. 445 to 1,646 m) above sea level. At the two sites where extensive sampling was done, the bacteria were recovered throughout the year. Generally, the recovery rates were highest in the fall and winter months and lowest during the spring and summer months. Campylobacter density did not show significant correlation with microbiological (plate counts of fecal and total coliforms, fecal streptococci, and heterotrophic bacteria) or physical (water temperature, pH, and conductivity) parameters.     

Effect of flow baffles on the dialysate flow distribution of hollow-fiber hemodialyzers: a nonintrusive experimental study using MRI

We used an innovative, nonintrusive MRI technique called the two-dimensional (2D) Phase-Contrast (2DPC) velocity-imaging technique to investigate the effect of flow baffles on the dialysate-side flow distribution in two different hollow-fiber hemodialyzers (A and B); each with flow rates between 200 and 1000 mL/min (3.33 x 10(-6) and 1.67 x 10(-5) m3/s). Our experimental results show that (1) the dialysate-side flow distribution was nonuniform with channeling flow occurred at the peripheral cross section of these hollow-fiber hemodialyzers, and (2) the existing designs of flow baffles failed to promote uniform dialysate-side flow distribution for all flow rates studies.