Role of microbial immigration in the colonization of apple leaves by Aureobasidium pullulans

The role of microbial immigration in the veinal colonization pattern of Aureobasidium pullulans on the adaxial surface of apple leaves was investigated in two experiments at two periods (early and late seasons) in 2004 by applying green fluorescent protein (GFP)-tagged blastospores to the foliage of orchard trees. Individual leaves were resampled by a semidestructive method immediately after inoculation (t(0)) and about 1 (t(1)), 2 (t(2)), and 3 (t(3)) weeks later. At t(0), there were no significant (P < or = 0.05) differences in densities (cells/mm(2)) on veinal (excluding midvein) sites and those on interveinal sites, but at all points thereafter, densities were significantly higher on veins. GFP-tagged A. pullulans cells remained primarily as singletons on interveinal regions (> or =90% at all points), while > or =20% of cells over veins at t(3) were in colonies of > or =4 cells. The colonies that developed from single cells placed on midveins and other veins were significantly larger than those that developed on interveinal regions of detached field and seedling leaves incubated under controlled conditions. Colonies primarily developed linearly along veins, reaching average colony sizes (72 h) of 24.4 +/- 12.7 (mean +/- standard deviation) cells. In contrast, colonies on interveinal regions tended to average only 2.9 +/- 1.3 cells, with less linearity. To examine the potential role of A. pullulans growth-inhibiting factors associated with interveinal features, single GFP-tagged A. pullulans cells in droplets previously incubated on interveinal sites were placed on midveins and compared to midvein colonies derived from cells in a water-only suspension. No differences in colony size resulted. Our results indicate that immigration limitation and growth-inhibiting factors are not the primary factors responsible for A. pullulans veinal colonization patterns in the field. Rather, indirect evidence suggests that growth-promoting substances occur locally in the veinal areas.     

DSM-IV “Criterion A” Schizophrenia Symptoms Across Ethnically Different Populations: Evidence for Differing Psychotic Symptom Content or Structural Organization?

There is significant variation in the expression of schizophrenia across ethnically different populations, and the optimal structural and diagnostic representation of schizophrenia are contested. We contrasted both lifetime frequencies of DSM-IV criterion A (the core symptom criterion of the internationally recognized DSM classification system) symptoms and types/content of delusions and hallucinations in transethnic schizophrenia populations from Australia (n = 776), India (n = 504) and Sarawak, Malaysia (n = 259), to elucidate clinical heterogeneity. Differences in both criterion A symptom composition and symptom content were apparent. Indian individuals with schizophrenia reported negative symptoms more frequently than other sites, whereas individuals from Sarawak reported disorganized symptoms more frequently. Delusions of control and thought broadcast, insertion, or withdrawal were less frequent in Sarawak than Australia. Curiously, a subgroup of 20 Indian individuals with schizophrenia reported no lifetime delusions or hallucinations. These findings potentially challenge the long-held view in psychiatry that schizophrenia is fundamentally similar across cultural groups, with differences in only the content of psychotic symptoms, but equivalence in structural form.     

The force-velocity relationship for the actin-based motility of Listeria monocytogenes

The intracellular movement of the bacterial pathogen Listeria monocytogenes has helped identify key molecular constituents of actin-based motility (recent reviews ). However, biophysical as well as biochemical data are required to understand how these molecules generate the forces that extrude eukaryotic membranes. For molecular motors and for muscle, force-velocity curves have provided key biophysical data to distinguish between mechanistic theories. Here we manipulate and measure the viscoelastic properties of tissue extracts to provide the first force-velocity curve for Listeria monocytogenes. We find that the force-velocity relationship is highly curved, almost biphasic, suggesting a high cooperativity between biochemical catalysis and force generation. Using high-resolution motion tracking in low-noise extracts, we find long trajectories composed exclusively of molecular-sized steps. Robust statistics from these trajectories show a correlation between the duration of steps and macroscopic Listeria speed, but not between average step size and speed. Collectively, our data indicate how the molecular properties of the Listeria polymerization engine regulate speed, and that regulation occurs during molecular-scale pauses.     

Chimeric mice reveal clonal development of pancreatic acini, but not islets

Intestinal crypt stem cells establish clonal descendants. To determine whether the pancreas is patterned by a similar process, we used embryonic stem (ES) cell chimeric mice, in which male ES cells were injected into female blastocysts. Fluorescence in situ hybridization for the Y chromosome (Y-FISH) revealed clonal patterning of ES-derived cells in the adult mouse small intestine and pancreas. Intestinal crypts were entirely male or entirely female. Villi contained columns of male or female epithelial cells, consistent with upward migration of cells from the crypts which surround them. Within the exocrine pancreas, acini were entirely male or entirely female, consistent with patterning from a single stem/progenitor cell. Pancreatic islets contained a mixture of male and female cells, consistent with patterning from multiple progenitors. Male-female chimeric mice demonstrate that the adult mouse exocrine pancreatic acinus is patterned from a single stem/progenitor cell, while the endocrine pancreas arises from multiple progenitors.     

Targeted deletion of the ATP binding domain of left-right dynein confirms its role in specifying development of left-right asymmetries.

Vertebrates develop distinct asymmetries along the left-right axis, which are consistently aligned with the anteroposterior and dorsoventral axes. The mechanisms that direct this handed development of left-right asymmetries have been elusive, but recent studies of mutations that affect left-right development have shed light on the molecules involved. One molecule implicated in left-right specification is left-right dynein (LRD), a microtubule-based motor protein. In the LRD protein of the inversus viscerum (iv) mouse, there is a single amino acid difference at a conserved position, and the lrd gene is one of many genes deleted in the legless (lgl) mutation. Both iv and lgl mice display randomized left-right development. Here we extend the analysis of the lrd gene at the levels of sequence, expression and function. The complete coding sequence of the lrd gene confirms its classification as an axonemal, or ciliary, dynein. Expression of lrd in the node at embryonic day 7.5 is shown to be symmetric. At embryonic day 8.0, however, a striking asymmetric expression pattern is observed in all three germ layers of the developing headfold, suggesting roles in both the establishment and maintenance of left-right asymmetries. At later times, expression of lrd is also observed in the developing floorplate, gut and limbs. These results suggest function for LRD protein in both ciliated and non-ciliated cells, despite its sequence classification as axonemal. In addition, a targeted mutation of lrd was generated that deletes the part of the protein required for ATP binding, and hence motor function. The resulting left-right phenotype, randomization of laterality, is identical to that of iv and lgl mutants. Gross defects in ciliary structure were not observed in lrd/lrd mutants. Strikingly, however, the monocilia on mutant embryonic node cells were immotile. These results prove the identity of the iv and lrd genes. Further, they argue that LRD motor function, and resulting nodal monocilia movement, are required for normal left-right development.     

Accumulation of vitamin E in potato (Solanum tuberosum) tubers

Vitamin E (tocopherol) is a powerful antioxidant essential for human health and synthesized only by photosynthetic organisms. The effects of over-expression of tocopherol biosynthetic enzymes have been studied in leaves and seeds, but not in a non-photosynthetic, below-ground plant organ. Genetic and molecular approaches were used to determine if increased levels of tocopherols can be accumulated in potato (Solanum tuberosum L.) tubers through metabolic engineering. Two transgenes were constitutively over-expressed in potato: Arabidopsis thaliana p-hydroxyphenylpyruvate dioxygenase (At-HPPD) and A. thaliana homogentisate phytyltransferase (At-HPT). α-Tocopherol levels in the transgenic plants were determined by high-performance liquid chromatography. In potato tubers, over-expression of At-HPPD resulted in a maximum 266% increase in α-tocopherol, and over-expression of At-HPT yielded a 106% increase. However, tubers from transgenic plants still accumulated approximately 10- and 100-fold less α-tocopherol than leaves or seeds, respectively. The results indicate that physiological and regulatory constraints may be the most limiting factors for tocopherol accumulation in potato tubers. Studying regulation and induction of tocopherol biosynthesis should reveal approaches to more effectively engineer crops with enhanced tocopherol content.