Plasma cell differentiation requires silencing of B cell transcription, while establishing antibody-secretory function and long-term survival. The transcription factors Blimp-1 and IRF4 are essential for plasma cell generation, however their function in mature plasma cells has remained elusive. We have found that while IRF4 was essential for plasma cell survival, Blimp-1 was dispensable. Blimp-1-deficient plasma cells retained their transcriptional identity, but lost the ability to secrete antibody. Blimp-1 regulated many components of the unfolded protein response (UPR), including XBP-1 and ATF6. The overlap of Blimp-1 and XBP-1 function was restricted to the UPR, with Blimp-1 uniquely regulating mTOR activity and plasma cell size. Thus, Blimp-1 is required for the unique physiological capacity of plasma cells that enables the secretion of protective antibody.

Compact metal probes: A solution for atomic force microscopy based tip-enhanced Raman spectroscopy Rev. Sci. Instrum. 83, 123708 (2012) Note: Radiofrequency scanning probe microscopy using vertically oriented cantilevers Rev. Sci. Instrum. 83, 126103 (2012) Switching spectroscopic measurement of surface potentials on ferroelectric surfaces via an open-loop Kelvin probe force microscopy method Appl. Phys. Lett. 101, 242906 (2012) Enhanced quality factors and force sensitivity by attaching magnetic beads to cantilevers for atomic force microscopy in liquid J. Appl. Phys. 112, 114324 (2012) Invited Review Article: High-speed flexure-guided nanopositioning: Mechanical design and control issues Rev. Sci. Instrum. 83, 121101 (2012) Additional information on Rev. Sci. Instrum. The spring constant of an atomic force microscope cantilever is often needed for quantitative measurements. The calibration method of Sader et al. [Rev. Sci. Instrum. 70, 3967 (1999)] for a rectangular cantilever requires measurement of the resonant frequency and quality factor in fluid (typically air), and knowledge of its plan view dimensions. This intrinsically uses the hydrodynamic function for a cantilever of rectangular plan view geometry. Here, we present hydrodynamic functions for a series of irregular and non-rectangular atomic force microscope cantilevers that are commonly used in practice. Cantilever geometries of arrow shape, small aspect ratio rectangular, quasi-rectangular, irregular rectangular, non-ideal trapezoidal cross sections, and V-shape are all studied. This enables the spring constants of all these cantilevers to be accurately and routinely determined through measurement of their resonant frequency and quality factor in fluid (such as air). An approximate formulation of the hydrodynamic function for microcantilevers of arbitrary geometry is also proposed. Implementation of the method and its performance in the presence of uncertainties and non-idealities is discussed, together with conversion factors for the static and dynamic spring constants of these cantilevers. These results are expected to be of particular value to the design and application of micro-and nanomechanical systems in general.

Background: Several virulence factors of Porphyromonas gingivalis have a novel C-terminal signal that directs secretion across the outer membrane. Results: The predicted catalytic amino acid of PG0026 was essential for the removal of this signal. Conclusion: PG0026 is a novel C-terminal signal peptidase. Significance: We have identified a novel signal peptidase of a new type of secretion system.

The cell wall (frustule) of the freshwater diatom Pinnularia viridis (Nitzsch) Ehrenberg is composed of an assembly of highly silicified components and associated organic layers. We used atomic force microscopy (AFM) to investigate the nanostructure and relationship between the outermost surface organics and the siliceous frustule components of live diatoms under natural hydrated conditions. Contact mode AFM imaging revealed that the walls were coated in a thick mucilaginous material that was interrupted only in the vicinity of the raphe fissure. Analysis of this mucilage by force mode AFM demonstrated it to be a nonadhesive, soft, and compressible material. Application of greater force to the sample during repeated scanning enabled the mucilage to be swept from the hard underlying siliceous components and piled into columns on either side of the scan area by the scanning action of the tip. The mucilage columns remained intact for several hours without dissolving or settling back onto the cleaned valve surface, thereby revealing a cohesiveness that suggested a degree of crosslinking. The hard silicified surfaces of the diatom frustule appeared to be relatively smooth when living cells were imaged by AFM or when field-emission SEM was used to image chemically cleaned walls. AFM analysis of P. viridis frustules cleaved in crosssection revealed the nanostructure of the valve silica to be composed of a conglomerate of packed silica spheres that were 44.8 Ϯ 0.7 nm in diameter. The silica spheres that comprised the girdle band biosilica were 40.3 Ϯ 0.8 nm in diameter. Analysis of another heavily silicified diatom, Hantzschia amphioxys (Ehrenberg) Grunow, showed that the valve biosilica was composed of packed silica spheres that were 37.1 Ϯ 1.4 nm and that silica particles from the girdle bands were 38.1 Ϯ 0.5 nm. These results showed little variation in the size range of the silica particles within a particular frustule component (valve or girdle band), but there may be differences in particle size between these components within a diatom frustule and significant differences are found between species.

Apical membrane antigen 1 of Plasmodium falciparum (PfAMA1) contains an N-terminal propeptide that is removed prior to the translocation of the mature protein onto the merozoite surface. We localized unprocessed PfAMA1 to the microneme organelles of the intraerythrocytic schizont. The results have suggested that the processed form of PfAMA1 translocates from the microneme compartment independently of another microneme protein, EBA175, which is also involved in the invasion of human erythrocytes.The clinical symptoms of malaria infection result from exponential expansion of parasite numbers during the asexual erythrocytic phase of the Plasmodium life cycle. The precise molecular events mediating erythrocyte invasion are not fully understood, but its rapid nature indicates that it is a tightly controlled process involving specific receptor-ligand interactions between host and parasite (reviewed in reference 7). Molecules located in the apical organelles, as well as those found on the merozoite surface, are believed to play crucial roles.Extracellular merozoites form an initially reversible attachment to circulating erythrocytes through molecules in the surface coat filaments of the parasite (18). Attached merozoites then reorient to bring the anterior apical pole into alignment with the erythrocyte plasma membrane. Next, an irreversible adhesion, the tight junction, forms between host and parasite membranes, coinciding with an indentation in the erythrocyte membrane and extrusion of the contents of the apical organelles (2, 6). Entry into the host cell is accomplished by posterior movement of the tight junction around the merozoite circumference. When the newly formed parasitophorous vacuole is sealed around the body of the merozoite, invasion is complete.In Plasmodium falciparum, proteins belonging to the erythrocyte binding protein family have been identified in the micronemes of developing and free merozoites. The best characterized of these is EBA175, which binds to sialic acid residues present on glycophorin A, a highly abundant erythrocyte surface protein (38).Proteins found in association with the merozoite surface and apical organelles offer considerable potential as components in a malaria vaccine (4). One of the leading candidates for inclusion in a subunit vaccine is apical membrane antigen 1 (AMA1). This molecule has been demonstrated to induce protection against parasite challenge in various animal model systems (3,12,15).P. falciparum AMA1 (PfAMA1) is synthesized in segmenting schizonts as a precursor protein of around 83 kDa, which is then processed N terminally to a 62-kDa form (13). This protein has the structural features of a type 1 integral membrane protein, with short transmembrane and cytoplasmic tail domains. It has previously been localized by immunofluorescence microscopy to the apical organelles and the surface of the merozoite (32), and immunoelectron microscopy (immuno-EM) suggested it to be resident in the rhoptry neck (13). The processed form of AMA1 is thought to translocate to the m...