Rab5-family guanine nucleotide exchange factors bind retromer and promote its recruitment to endosomes

The retromer complex facilitates the sorting of integral membrane proteins from the endosome to the late Golgi. In mammalian cells, the efficient recruitment of retromer to endosomes requires the lipid phosphatidylinositol 3-phosphate (PI3P) as well as Rab5 and Rab7 GTPases. However, in yeast, the role of Rabs in recruiting retromer to endosomes is less clear. We identified novel physical interactions between retromer and the Saccharomyces cerevisiae VPS9-domain Rab5-family guanine nucleotide exchange factors (GEFs) Muk1 and Vps9. Furthermore, we identified a new yeast VPS9 domain-containing protein, VARP-like 1 (Vrl1), which is related to the human VARP protein. All three VPS9 domain–containing proteins show localization to endosomes, and the presence of any one of them is necessary for the endosomal recruitment of retromer. We find that expression of an active VPS9-domain protein is required for correct localization of the phosphatidylinositol 3-kinase Vps34 and the production of endosomal PI3P. These results suggest that VPS9 GEFs promote retromer recruitment by establishing PI3P-enriched domains at the endosomal membrane. The interaction of retromer with distinct VPS9 GEFs could thus link GEF-dependent regulatory inputs to the temporal or spatial coordination of retromer assembly or function.     

Effects of temporal patterning of predation threat on movement of a stream fish: evaluating an intermediate threat hypothesis

The addition of nocturnal, Hoplias malabaricus, and diurnal, Crenicichla alta, predatory fishes downstream of barrier waterfalls increases predation threat for a killifish, Rivulus hartii, in Trinidadian streams. We hypothesized that the diel patterning of predation risk would affect prey movement rates, and tested this hypothesis by comparing movement in river sites/zones containing both the nocturnal and diurnal predator with movement in river sites/zones containing only the nocturnal taxon. We evaluated this prediction in the framework of an intermediate threat hypothesis (ITH) that holds that movement will be highest at some intermediate level of threat. We marked prey fish in study sites in two watersheds of a river, each with waterfalls that divided the river into three zones: a predator absent zone (P0), a zone with one nocturnal predator (P1), and a zone with one nocturnal and one diurnal predator (P2), and tested the ITH prediction that movement will be ordered as P0<P1>P2. The single predator promoted longitudinal movement by Rivulus (P0<P1), while zones with the two predators retarded movement for small Rivulus (P1>P2) as predicted by the ITH. However, movement by larger, less vulnerable Rivulus remained elevated (P1=P2 or P2>P1). A displacement experiment in each zone found that threat tended to reduce the probability of a displaced fish reaching home, but the two predator zones did not differ from one another in their effect on this probability. Hence, the prediction that predator activity over the full 24 h diel cycle would retard movement, P2<P1, was not supported with respect to homing. Because habitat and predator communities change predictably from headwater streams to larger rivers in many lotic ecosystems, we present a conceptual model for predicting fish movement behavior along this continuum. The model posits an important role for predation threat, and the size and spacing of refuge patches, suggesting that human alterations of these factors will affect the natural movement of fish in streams.     

The immediate effect of individual manipulation techniques on pulmonary function measures in persons with chronic obstructive pulmonary disease

Background

The use of manipulation has long been advocated in the treatment of chronic obstructive pulmonary disease (COPD), but few randomized controlled clinical trials have measured the effect of manipulation on pulmonary function. In addition, the effects of individual manipulative techniques on the pulmonary system are poorly understood. Therefore, the purpose of this study was to determine the immediate effects of four osteopathic techniques on pulmonary function measures in persons with COPD relative to a minimal-touch control protocol.

Methods

Persons with COPD aged 50 and over were recruited for the study. Subjects received five, single-technique treatment sessions: minimal-touch control, thoracic lymphatic pump (TLP) with activation, TLP without activation, rib raising, and myofascial release. There was a 4-week washout period between sessions. Protocols were given in random order until all five techniques had been administered. Pulmonary function measures were obtained at baseline and 30-minutes posttreatment. For the actual pulmonary function measures and percent predicted values, Wilcoxon signed rank tests were used to test within-technique changes from baseline. For the percent change from baseline, Friedman tests were used to test for between-technique differences.

Results

Twenty-five subjects were enrolled in the study. All four tested osteopathic techniques were associated with adverse posttreatment changes in pulmonary function measures; however, different techniques changed different measures. TLP with activation increased posttreatment residual volume compared to baseline, while TLP without activation did not. Side effects were mild, mostly posttreatment chest wall soreness. Surprisingly, the majority of subjects believed they could breathe better after receiving osteopathic manipulation.

Conclusion

In persons with COPD, TLP with activation, TLP without activation, rib raising, and myofascial release mildly worsened pulmonary function measures immediately posttreatment relative to baseline measurements. The activation component of the TLP technique appears to increase posttreatment residual volume. Despite adverse changes in pulmonary function measures, persons with COPD subjectively reported they benefited from osteopathic manipulation.     

Cdc42 and Gsk3 modulate the dynamics of radial glial growth, inter-radial glial interactions and polarity in the developing cerebral cortex

Polarized radial glia are crucial to the formation of the cerebral cortex. They serve as neural progenitors and as guides for neuronal placement in the developing cerebral cortex. The maintenance of polarized morphology is essential for radial glial functions, but the extent to which the polarized radial glial scaffold is static or dynamic during corticogenesis remains an open question. The developmental dynamics of radial glial morphology, inter-radial glial interactions during corticogenesis, and the role of the cell polarity complexes in these activities remain undefined. Here, using real-time imaging of cohorts of mouse radial glia cells, we show that the radial glial scaffold, upon which the cortex is constructed, is highly dynamic. Radial glial cells within the scaffold constantly interact with one another. These interactions are mediated by growth cone-like endfeet and filopodia-like protrusions. Polarized expression of the cell polarity regulator Cdc42 in radial glia regulates glial endfeet activities and inter-radial glial interactions. Furthermore, appropriate regulation of Gsk3 activity is required to maintain the overall polarity of the radial glia scaffold. These findings reveal dynamism and interactions among radial glia that appear to be crucial contributors to the formation of the cerebral cortex. Related cell polarity determinants (Cdc42, Gsk3) differentially influence radial glial activities within the evolving radial glia scaffold to coordinate the formation of cerebral cortex.     

Hybridization between <Emphasis Type="Italic">Schoenoplectus</Emphasis> sedges across Chesapeake Bay marshes

Hybridization is an evolutionary mechanism capable of enhancing adaptive potential, especially among species in fragmented or disturbed ecosystems like coastal marshes. In this study, we evaluated whether hybridization might influence adaptive responses in coastal marshes that are susceptible to the effects of global environmental change. To do so, we examined the extent and nature of hybridization between Schoenoplectus americanus and S. pungens, two ecologically dominant sedges in low-lying marshes across Chesapeake Bay (USA). Observed patterns of variation at genetically based morphological traits, cpDNA and nuclear microsatellite markers confirm that introgressive hybridization occurs between the two species. Comparisons of microsatellite and cpDNA profiles found that hybridization is reciprocal, although a disproportionate number of hybrids exhibit genomic asymmetries favoring S. americanus. AIC model selection consistently identified latitude as the strongest explanatory variable for the distribution of parental species, although discriminant analysis indicated that distributions also correspond to variation in environmental conditions. Discriminant analysis further indicated that ecological correlates of hybrid and S. americanus genotypes are similar, but not uniformly so. These findings indicate that the boundary between S. americanus and S. pungens is porous, and that hybridization could influence responses of one or both species to changing environmental regimes.     

Energy determinants GAPDH and NDPK act as genetic modifiers for hepatocyte inclusion formation

Genetic factors impact liver injury susceptibility and disease progression. Prominent histological features of some chronic human liver diseases are hepatocyte ballooning and Mallory-Denk bodies. In mice, these features are induced by 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) in a strain-dependent manner, with the C57BL and C3H strains showing high and low susceptibility, respectively. To identify modifiers of DDC-induced liver injury, we compared C57BL and C3H mice using proteomic, biochemical, and cell biological tools. DDC elevated reactive oxygen species (ROS) and oxidative stress enzymes preferentially in C57BL livers and isolated hepatocytes. C57BL livers and hepatocytes also manifested significant down-regulation, aggregation, and nuclear translocation of glyceraldehyde 3-phosphate dehydrogenase (GAPDH). GAPDH knockdown depleted bioenergetic and antioxidant enzymes and elevated hepatocyte ROS, whereas GAPDH overexpression decreased hepatocyte ROS. On the other hand, C3H livers had higher expression and activity of the energy-generating nucleoside-diphosphate kinase (NDPK), and knockdown of hepatocyte NDPK augmented DDC-induced ROS formation. Consistent with these findings, cirrhotic, but not normal, human livers contained GAPDH aggregates and NDPK complexes. We propose that GAPDH and NDPK are genetic modifiers of murine DDC-induced liver injury and potentially human liver disease.