Actions of Rho family small G proteins and p21-activated protein kinases on mitogen-activated protein kinase family members.

The mitogen-activated protein (MAP) kinases are a family of serine/threonine kinases that are regulated by distinct extracellular stimuli. The currently known members include extracellular signal-regulated protein kinase 1 (ERK1), ERK2, the c-Jun N-terminal kinase/stress-activated protein kinases (JNK/SAPKs), and p38 MAP kinases. We find that overexpression of the Ste20-related enzymes p21-activated kinase 1 (PAK1) and PAK2 in 293 cells is sufficient to activate JNK/SAPK and to a lesser extent p38 MAP kinase but not ERK2. Rat MAP/ERK kinase kinase 1 can stimulate the activity of each of these MAP kinases. Although neither activated Rac nor the PAKs stimulate ERK2 activity, overexpression of either dominant negative Rac2 or the N-terminal regulatory domain of PAK1 inhibits Ras-mediated activation of ERK2, suggesting a permissive role for Rac in the control of the ERK pathway. Furthermore, constitutively active Rac2, Cdc42hs, and RhoA synergize with an activated form of Raf to increase ERK2 activity. These findings reveal a previously unrecognized connection between Rho family small G proteins and the ERK pathway.     

Assessment of lead availability in soils contaminated by mine spoil

The uptake of lead by two contrasting plant species, radish and red fescue, grown in soils contaminated by mine spoil was investigated. Uptake was found to be poorly correlated either with pH or total Pb concentration in the soils. By contrast, a good correlation was obtained, particularly for red fescue, between Pb uptake and Pb concentration in the solution of equilibrated soil suspensions over a wide range of soil pH, total soil Pb and soil solution Pb concentration.Calculations suggested a similar order of magnitude in the total amounts of Pb taken up by the plants and Pb in the soil solution of the root zone, justifying the latter as a good index of Pb-availability. ei]Section editor: A C Borstlap     

On the probability of loss of new mutations in the presence of linkage disequilibrium

A new selectively neutral mutation occurs in a multilocus genetic background that has achieved a stable equilibrium at which there is a linkage disequilibrium. Perturbation techniques are applied to an extension of the branching process formulation of Fisher in order to address the question of extinction probabilities. We show that under appropriate conditions the probability of extinction of the new mutant is increased by the existence of linkage disequilibrium in the genetic background.Research supported in part by NIH grant GM 28016     

Root Morphology and Nitrogen Uptake of Maize Simultaneously Supplied with Ammonium and Nitrate in a Split-root System

We studied the response of maize (Zea mays L. cv. Anjou 256)to a simultaneous, but separated supply of ammonium and nitrate(localized supply, LS). A split-root system was used to supplyhalf of the roots with ammonium and the other half with nitrate.A homogeneously distributed supply of both nitrogen forms (HS)was the control treatment. Seedlings were grown for 12 d fromthe two-leaf to the three-leaf stage in hydroponics at threepH levels (4, 5·5 and 7). The total N concentration was3 mol m^-3. The split-root system was established by removingthe seminal root system and using only four nodal roots perplant. Total root length and root surface area were recordedautomatically with a modified Delta- T area meter. Other morphologicalroot traits (such as main axis length and diameter, number,density, and length of laterals) were recorded manually. Uptakeof ammonium and nitrate was measured by the depletion of thenutrient solution. As compared with LS, HS was superior in shootand root DM, total root length and root surface area, ammoniumand nitrate uptake and shoot nitrogen concentration, irrespectiveof pH level. This indicates that, also under field conditions,mixed ammonium and nitrate fertilization is only beneficialto plant growth if both N forms are evenly distributed in thesoil. At both HS and LS, ascending pH increased the ammonium:nitrateuptake ratio. At LS, declining pH induced a considerable shiftin the distribution of root DM, root length, and root surfacearea the nitrate-fed compartment.Copyright 1993, 1999 AcademicPress Maize, Zea may L., ammonium, nitrate, pH, root morphology, split-root     

Variable subcellular localization of glycosphingolipids

Although most glycosphingolipids (GSLs) are thought to be locatedin the outer leaflet of the plasma membrane, recent evidenceindicates that GSLs are also associated with intracellular organelles.We now report that the subcellular localization of GSLs variesdepending on the GSL structure and cell type. GSL localizationwas determined by indirect immunofluorescence microscopy offixed permeabilized cells. A single GSL exhibited variable subcellularlocalization in different cells. For example, antibody to GalCeris localized primarily to the plasma membrane of HaCaT II-3keratinocytes, but to intracellular organelies in other epithelialcells. GalCer is localized to small vesicles and tubulovesicularstructures in MDCK cells, and to the surface of phase-denselipid droplets in HepG2 hepatoma cells. Furthermore, withina single cell type, individual GSLs were found to exhibit differentpatterns of subcellular localization. In HepG2 cells, LacCerwas associated with small vesicles, which differed from thephase-dense vesicles stained by anti-GalCer, and Gb4Cer wasassociated with the intermediate filaments of the cytoskeleton.Both anti-GalCer and monoclonal antibody A2B5, which binds polysialogangliosides,localized to mitochondria. The distinct subcellular localizationpatterns of GSLs raise interesting questions about their functionsin different organelles. Together with published data on theenrichment of GSLs in specific organelles and in apical plasmamembrane, these findings indicate the existence of specificsorting mechanisms that regulate the intracellular transportand localization of GSLs. cytoskeleton glycosphingolipid intracellular organelles mitochondria subcellular localization     

Effect of Ethnicity and Geographical Location on Body Weight,Dietary Restraint,and Abnormal Eating Attitudes

Previous studies have examined the effect of ethnicity on obesity, concerns about shape and weight, and attitudes about eating. We hypothesized that geographical location would also influence these variables, and that students growing up in the northern part of the United States and attending northern colleges would differ from students from the South. To examine this, we studied a random sample of 275 African-Americans (AA) and 224 white college students in the entering class of two northern colleges (University of Pittsburgh or University of Massachusetts) or two southern colleges (Augusta or Paine College). All subjects were weighed and completed the Revised Restraint Scale and the EAT-26. AA women were heavier than white women, with no differences due to geographical location. Despite being thinner, white women reported more dietary restraint than AA women. This difference between AA and white women was apparent in both northern and southern college students. In contrast, geographical location was the strongest determinant of bulimic attitudes; both men and women at northern colleges reported higher bulimia scores than those at southern schools. Thus ethnicity appears to be a major determinant of body weight and attitudes about shape and dieting, whereas geographical location appears to exert greater influence on bulimic attitudes.