Megakaryocyte interaction with subendothelial extracellular matrix is associated with adhesion, platelet-like shape change, and thromboxane A2 production

We have examined the morphological and secretory behavior of rat and guinea pig megakaryocytes exposed for up to 24 hours to extracellular matrix produced by cultured bovine endothelial cells. By phase-contrast microscopy of living cells and in more detail by scanning electron microscopy, the megakaryocytes showed a nonreversible adherence, an extensive formation of filopodia around the periphery like the rays of the sun, and a tendency toward flattening. These filopodia were generally linear with attenuated tips and were larger than, but resembled the filopodia of, rat or guinea pig platelets exposed to this extracellular matrix. In contrast, isolated megakaryocytes on glass or on uncoated plastic surfaces did not show these responses; adherence, in the face of gentle agitation before fixation, was minimal, with rare filopodia and no flattening. Megakaryocytes that interacted with the extracellular matrix produced significant amounts of thromboxane A2, but this did not occur on uncoated surfaces and could not be attributed to other contaminating cells in the megakaryocyte suspensions. The appearance in megakaryocytes of these typical platelet responses indicates that megakaryocytes acquire the functional capabilities of platelets by the synthesis and assembly of platelet substances and organelles. Thromboxane production by megakaryocytes stimulated by the extracellular matrix is a readily quantifiable measure of this capacity.     

EMTALA: the basics

The Emergency Medical Treatment and Active Labor Act (EMTALA) is the federal legislation governing the transfer of patients. This law is often confusing for healthcare providers. For this reason, it is often difficult for providers to understand what elements of this law apply to their practice. This article outlines the EMTALA requirements to clearly relay the critical elements of this important piece of legislation and to illustrate how EMTALA applies to hospital nursing practice. All nurses in administrative and management roles need to be aware of the requirements of this law in order to educate and guide their nursing staff so that the facility remains in compliance.     

Teamwork in the viscous oceanic microscale

Nutrient acquisition is crucial for oceanic microbes, and competitive solutions to solve this challenge have evolved among a range of unicellular protists. However, solitary solutions are not the only approach found in natural populations. A diverse array of oceanic protists form temporary or even long-lasting attachments to other protists and marine aggregates. Do these planktonic consortia provide benefits to their members? Here, we use empirical and modeling approaches to evaluate whether the relationship between a large centric diatom, Coscinodiscus wailesii, and a ciliate epibiont, Pseudovorticella coscinodisci, provides nutrient flux benefits to the host diatom. We find that fluid flows generated by ciliary beating can increase nutrient flux to a diatom cell surface four to 10 times that of a still cell without ciliate epibionts. This cosmopolitan species of diatom does not form consortia in all environments but frequently joins such consortia in nutrient-depleted waters. Our results demonstrate that symbiotic consortia provide a cooperative alternative of comparable or greater magnitude to sinking for enhancement of nutrient acquisition in challenging environments.

Global models of oxygen and carbon dioxide alterations depend upon transfer rates between small phytoplankton cells and surrounding surface waters of the world’s oceans (1–3). Although these cells are important on large scales, their individual interactions occur at microscopic dimensions that are dominated by viscosity. In this viscous environment, critical cellular processes, such as the exchange of nutrients, metabolites, and wastes, rely upon diffusion (4). While diffusion is an effective means of nutrient transport for the smallest microbes (5), it also creates a depleted region around the cell surface, referred to as the diffusion boundary layer (DBL), that limits nutrient consumption and cell growth (6, 7). The DBL for a cell at rest extends nine cell radii from the cell surface before the nutrient concentration reaches 90% of ambient levels (8), creating formidable disadvantages for nutrient acquisition by large cells requiring nutrient diffusion across large distances relative to their cell size (9). Phytoplankton have evolved mechanisms to mitigate the limitations of diffusive transfer rates by swimming or sinking (10) to generate relative motion between the cell and surrounding fluid. Diatoms—barrel-shaped, nonmotile eukaryotes—are considered to be one of the most ecologically important groups of phytoplankton (11–14) that absorb nutrients across their whole cell surface (15) but often increase sinking rates when experiencing nutrient limitation (16). Sinking thins the DBL surrounding the diatom cell and reduces the distance over which diffusion limits nutrient transport (8, 17). One potential disadvantage of this mechanism for DBL reduction is the high probability for a cell to sink out of sunlit regions, and sinking diatoms are major contributors to organic mass flux from surface to deep oceanic waters (1). A widespread but unevaluated alternative for such large cells involves teamwork with other smaller, motile cells that combine to form multicell consortia. Consortia are typically comprised of larger nonmotile host cells with smaller, surface-adhering motile cells termed epibionts. Although infrequently studied, epibionts are ubiquitous in the micrometer-scale world of planktonic organisms (18), and flagellated or ciliated epibionts often attach to larger objects (19) or marine snow (20). The selective forces favoring epibiont attachment remain in question. A range of fluid dynamic effects on prey encounter as well as biological factors such as reduced predator encounter risk or elevated prey availability surrounding host attachment sites have been proposed to explain the widespread nature of epibiont attachment (21, 22). However, the movement of motile epibiont cilia or flagella alters flows and, hence, creates an altered fluid dynamic environment surrounding the consortia. What are the consequences for the consortium host—does a larger, nonmotile cell benefit by membership in consortia? While advantages to the epibiont have been examined, the impacts on the host cells within a consortium have remained largely unconsidered. One reason for this is that physical associations between members of consortia are often temporary, and the short time scales of these relationships have hampered direct evaluation of the fluid mechanical interactions between consortium members.Here, we describe experimental work in combination with mathematical models that quantify the effect of the epibiont’s advective currents on nutrient availability to host cells within consortia formed by a large diatom, Coscinodiscus wailesii, and its peritrich ciliate epibiont, Pseudovorticella coscinodisci (Fig. 1A). Consortia composed of C. wailesii and P. coscinodisci are common along the Atlantic coast of South America (23, 24) and have provided a valuable opportunity for measuring fluid interactions characterizing a planktonic host–epibiont association.Open in a separate windowFig. 1.Diatom–ciliate association: (A) diatom C. wailesii and its epibiont P. coscinodisci. Scale bars represent 100 microns in length. (B) Flow around a single ciliate directed toward the diatom cell surface. (C) Velocity field for the same diatom–ciliate pair with a blue line indicating the transect line used for measurement of flow field velocities. The magenta segment represents the microcurrent component that directly intercepts the ciliary crown.     

Association of IFNL3 and IFNL4 polymorphisms with liver‐related mortality in a multiracial cohort of HIV/HCV‐coinfected women

African Americans coinfected with HIV and hepatitis C virus (HCV) have lower liver‐related mortality than Caucasians and Hispanics. While genetic polymorphisms near the IFNL3 and IFNL4 genes explain a significant fraction of racial differences in several HCV‐related outcomes, the impact of these variants on liver‐related mortality has not been investigated. We conducted a cohort study of HIV/HCV‐coinfected women followed in the multicentre, NIH‐funded Women's Interagency HIV Study (WIHS) to investigate whether 10 polymorphisms spanning the IFN‐λ region were associated with liver‐related mortality by dominant, recessive or additive genetic models. We also considered whether these polymorphisms contributed to previously reported differences in liver‐related death by race/ethnicity (ascertained by self‐report and ancestry informative markers). Among 794 coinfected women, there were 471 deaths including 55 liver‐related deaths during up to 18 years of follow‐up. On adjusted analysis, rs12980275 GG genotype compared to AG+AA hazards ratios [(HR) 0.36, 95% CI 0.14–0.90, P = 0.029] and rs8109886 AA genotype compared to CC+AC (HR 0.67, 95% CI 0.45–0.99, P = 0.047) were most strongly associated with liver‐related death although these associations were no longer significant after adjusting for race/ethnicity (HR 0.41, 95% CI 0.16–1.04, P = 0.060 and HR 0.78, 95% CI 0.51–1.19, P = 0.25, respectively). African American women had persistently lower liver‐related death independent of IFN‐λ variants (HRs ≤ 0.44, P values ≤ 0.04). The lower risk of death among African American HIV/HCV‐coinfected women is not explained by genetic variation in the IFN‐λ region suggesting, that other genetic, behavioural and/or environmental factors may contribute to racial/ethnic differences in liver‐related mortality.