The Role of Relationships in the Professional Formation of Physicians

BACKGROUND: Studies of the professional development of physicians highlight the important effect that the learning environment, or \"hidden curriculum,\" has in shaping student attitudes, behaviors, and values. We conducted this study to better understand the role that relationships have in mediating these effects of the hidden curriculum. [See PDF for complete abstract]

Activation of DegP chaperone-protease via formation of large cage-like oligomers upon binding to substrate proteins.

Cells use molecular chaperones and proteases to implement the essential quality control mechanism of proteins. The DegP (HtrA) protein, essential for the survival of Escherichia coli cells at elevated temperatures with homologues found in almost all organisms uniquely has both functions. Here we report a mechanism for DegP to activate both functions via formation of large cage-like 12- and 24-mers after binding to substrate proteins. Cryo-electron microscopic and biochemical studies revealed that both oligomers are consistently assembled by blocks of DegP trimers, via pairwise PDZ1-PDZ2 interactions between neighboring trimers. Such interactions simultaneously eliminate the inhibitory effects of the PDZ2 domain. Additionally, both DegP oligomers were also observed in extracts of E. coli cells, strongly implicating their physiological importance.

Function and formation of $\beta$1,4-galactosyltransferase-specific adhesions during growth and differentiation of F9 embryonal carcinoma cells

Galactosyltransferase (GalTase) is localized in the Golgi, where it functions in oligosaccharide synthesis, as well as on the cell surface where it serves as a cell adhesion molecule. GalTase-specific adhesions are functional in a number of important biological events, including F9 embryonal carcinoma (EC) cell adhesions. GalTase-based adhesions are formed by recognition and binding to terminal N-acetylglucosamine (GlcNAc) residues on its glycoprotein counterpart on adjacent cell surfaces. The object of this work has been to investigate the formation and function of GalTase-specific adhesions during F9 cell growth and differentiation. We initially investigated GalTase synthesis during differentiation and found that the increase in GalTase activity was specific for the Golgi compartment; surface GalTase levels remained constant during differentiation. These data indicated that the increase in cell adhesions expected with increased cell-matrix interaction in differentiated F9 cells is not the consequence of increased surface GalTase expression and, more interestingly, that the two pools of GalTase are under differential regulation. Synthesis and recognition of the consociate glycoprotein component was next investigated. Surface GalTase recognized several surface glycoproteins in a pattern that changes with differentiation. Uvomorulin, lysosome-associated membrane protein-1 (LAMP-1), and laminin were recognized by surface GalTase and are, therefore, potential components in GalTase-specific adhesions. Furthermore, these interactions were aberrant in an adhesion-defective F9 cell line that results, at least in part, from abnormal oligosaccharide synthesis. The function played by surface GalTase in growth and induction of differentiation was examined. Inhibition of surface GalTase function by a panel of reagents inhibited F9 cell growth. GalTase expression at both the transcription and protein levels were differentially regulated during the cell cycle, with surface expression greatest in the G1 phase. Disruption of GalTase adhesion by exposure to anti-GalTase antibodies during this period resulted in extension of the G2 phase, a result similar to that seen with agents known to inhibit growth and induce differentiation. Finally, other studies have suggested that a subset of cell adhesion molecules have the capability to induce differentiation in EC cells systems. We have determined in F9 cells that dissociating GalTase adhesion by galactosylation of and release of the consociate glycoproteins induces differentiation, as defined by increased laminin synthesis. The ability to induce differentiation by surface galactosylation was greatest in cells grown in cultures promoting cell-cell adhesions, relative to cultures with minimal cell-cell interactions. ^

Studies of subcellular localization and complex formation of the Agrobacterium tumefaciens transport ATPase VirB11

The VirB11 ATPase is an essential component of an Agrobacterium tumefaciens type IV bacterial secretion system that transfers oncogenic nucleoprotein complexes to susceptible plant cells. This dissertation investigates the subcellular localization and homo-oligomeric state of the VirB11 ATPase in order to provide insights about the assembly of the protein as a subunit of this membrane-associated transfer system. Subcellular fractionation studies and quantitative immunoblot analysis demonstrated that $\sim$30% of VirB11 partitioned as soluble protein and $\sim$70% was tightly associated with the bacterial cytoplasmic membrane. No differences were detected in VirB11 subcellular localization and membrane association in the presence or absence of other transport system components. Mutations in virB11 affecting protein function were mapped near the amino terminus, just upstream of a region encoding a Walker 'A' nucleotide-binding site, and within the Walker 'A' motif partitioned almost exclusively with the cytoplasmic membrane, suggesting that an activity associated with nucleotide binding could modulate the affinity of VirB11 for the cytoplasmic membrane. Merodiploid analysis of VirB11 mutant and truncation derivatives provided strong evidence that VirB11 functions as a homo- or heteromultimer and that the C-terminal half of VirB11 contains a protein interaction domain. A combination of biochemical and molecular genetic approaches suggested that VirB11 and the green fluorescence protein (GFP) formed a mixed multimer as demonstrated by immunoprecipitation experiments with anti-GFP antibodies. Second, a hybrid protein composed of VirB11 fused to the N-terminal DNA-binding domain of bacteriophage $\lambda$ cI repressor conferred immunity to $\lambda$ superinfection, demonstrating that VirB11 self-association promotes dimerization of the chimeric repressor. A conserved Walker 'A' motif, though required for VirB11 function in T-complex export, was not necessary for VirB11 self-association. Sequences in both the N- and the C-terminal halves of the protein were found to contribute to self-association of the full length protein. Chemical cross-linking experiments with His$\sb6$ tagged VirB11 suggested that VirB11 probably assembles into a higher order homo-oligomeric complex. ^

NADPH oxidase-independent formation of extracellular DNA traps by basophils

Basophils are primarily associated with a proinflammatory and immunoregulatory role in allergic diseases and parasitic infections. Recent studies have shown that basophils can also bind various bacteria both in the presence and the absence of opsonizing Abs. In this report, we show that both human and mouse basophils are able to produce mitochondrial reactive oxygen species and to form extracellular DNA traps upon IL-3 priming and subsequent activation of the complement factor 5 a receptor or FcεRI. Such basophil extracellular traps (BETs) contain mitochondrial, but not nuclear DNA, as well as the granule proteins basogranulin and mouse mast cell protease 8. BET formation occurs despite the absence of any functional NADPH oxidase in basophils. BETs can be found in both human and mouse inflamed tissues, suggesting that they also play a role under in vivo inflammatory conditions. Taken together, these findings suggest that basophils exert direct innate immune effector functions in the extracellular space.

Rat lungs show a biphasic formation of new alveoli during postnatal development

Roughly 90% of the gas-exchange surface is formed by alveolarization of the lungs. To the best of our knowledge, the formation of new alveoli has been followed in rats only by means of morphological description or interpretation of semiquantitative data until now. Therefore, we estimated the number of alveoli in rat lungs between postnatal days 4 and 60 by unambiguously counting the alveolar openings. We observed a bulk formation of new alveoli between days 4 and 21 (17.4 times increase from 0.8 to 14.3 millions) and a second phase of continued alveolarization between days 21 and 60 (1.3 times increase to 19.3 million). The (number weighted) mean volume of the alveoli decreases during the phase of bulk alveolarization from ∼593,000 μm(3) at day 4 to ∼141,000 μm(3) at day 21, but increases again to ∼298,000 μm(3) at day 60. We conclude that the "bulk alveolarization" correlates with the mechanism of classical alveolarization (alveolarization before the microvascular maturation is completed) and that the "continued alveolarization" follows three proposed mechanisms of late alveolarization (alveolarization after microvascular maturation). The biphasic pattern is more evident for the increase in alveolar number than for the formation of new alveolar septa (estimated as the length of the free septal edge). Furthermore, a striking negative correlation between the estimated alveolar size and published data on retention of nanoparticles was detected.

A Process Model of the Formation of Spatial Presence Experiences

In order to bridge interdisciplinary differences in Presence research and to establish connections between Presence and “older” concepts of psychology and communication, a theoretical model of the formation of Spatial Presence is proposed. It is applicable to the exposure to different media and intended to unify the existing efforts to develop a theory of Presence. The model includes assumptions about attention allocation, mental models, and involvement, and considers the role of media factors and user characteristics as well, thus incorporating much previous work. It is argued that a commonly accepted model of Spatial Presence is the only solution to secure further progress within the international, interdisciplinary and multiple-paradigm community of Presence research.

Formation of supramolecular polymers by chrysene oligomers

Supramolecular assembly of π-conjugated systems is of large interested due to the possibility to use them in electronic devices.[1] Chrysene is a polyaromatic hydrocarbon which has been studied e.g for organic light-emitting diodes (OLEDs).[2] In continuation of our previous work involving the supramolecular polymerisation of pyrene oligomers [3] an oligomer consisting of three chrysenes linked by phophodiesters was synthesised (Chry3). UV-Vis measurements show that aggregates of Chry3 are formed in aqueous medium. This is illustrated by general hypochromicity, a change in vibronic band intensities and, in particular, the appearance of a red-shifted absorption band in the S0 → S2 transition. The data suggest the formation of J-aggregates. The formation of supramolecular polymers is further studied by temperature-dependent absorption- and fluorescence measurements, and by atomic force microscopy (AFM).

Bioresorbable vascular scaffold treatment induces the formation of neointimal cap that seals the underlying plaque without compromising the luminal dimensions: a concept based on serial optical coherence tomography data.

Aims: To evaluate the implications of an Absorb bioresorbable vascular scaffold (Absorb BVS) on the morphology of the superficial plaques. Methods and results: Forty-six patients who underwent Absorb BVS implantation and 20 patients implanted with bare metal stents (BMS) who had serial optical coherence tomographic examination at baseline and follow-up were included in this analysis. The thin-capped fibroatheromas (TCFA) were identified in the device implantation regions and in the adjacent native coronary segments. Within all regions, circumferential locations of TCFA and calcific tissues were identified, and the neointimal thickness was measured at follow-up. At six to 12-month follow-up, only 8% of the TCFA detected at baseline were still present in the Absorb BVS and 27% in the BMS implantation segment (p=0.231). Sixty percent of the TCFA in native segments did not change their phenotype at follow-up. At short-term follow-up, significant reduction in the lumen area of the BMS was noted, which was higher compared to that reported in the Absorb BVS group (-2.11±1.97 mm2 vs. -1.34±0.99 mm2, p=0.026). In Absorb BVS, neointima tissue continued to develop at midterm follow-up (2.17±0.48 mm2 vs. 1.38±0.52 mm2, p<0.0001) and covered the underlying tissues without compromising the luminal dimensions (5.93±1.49 mm2 vs. 6.14±1.49 mm2, p=0.571) as it was accommodated by the expanded scaffold (8.28±1.74 mm2 vs. 7.67±1.28 mm2, p<0.0001). Conclusions: Neointimal tissue develops following either Absorb BVS or BMS implantation and shields lipid tissues. The neointimal response in the BMS causes a higher reduction of luminal dimensions compared to the Absorb BVS. Thus, Absorb BVS may have a value in the invasive re-capping of high-risk plaques.

VirB6 is required for stabilization of VirB5 and VirB3 and formation of VirB7 homodimers in Agrobacterium tumefaciens.

VirB6 from Agrobacterium tumefaciens is an essential component of the type IV secretion machinery for T pilus formation and genetic transformation of plants. Due to its predicted topology as a polytopic inner membrane protein, it was proposed to form the transport pore for cell-to-cell transfer of genetic material and proteinaceous virulence factors. Here, we show that the absence of VirB6 leads to reduced cellular levels of VirB5 and VirB3, which were proposed to assist T pilus formation as minor component(s) or assembly factor(s), respectively. Overexpression of virB6 in trans restored levels of cell-bound and T pilus-associated VirB5 to wild type but did not restore VirB3 levels. Thus, VirB6 has a stabilizing effect on VirB5 accumulation, thereby regulating T pilus assembly. In the absence of VirB6, cell-bound VirB7 monomers and VirB7-VirB9 heterodimers were reduced and VirB7 homodimer formation was abolished. This effect could not be restored by expression of VirB6 in trans. Expression of TraD, a component of the transfer machinery of the IncN plasmid pKM101, with significant sequence similarity to VirB6, restored neither protein levels nor bacterial virulence but partly permitted T pilus formation in a virB6 deletion strain. VirB6 may therefore regulate T pilus formation by direct interaction with VirB5, and wild-type levels of VirB3 and VirB7 homodimers are not required.