Disc and Actin Associated Protein 1 influences attachment in the intestinal parasite Giardia lamblia.

The deep-branching eukaryote Giardia lamblia is an extracellular parasite that attaches to the host intestine via a microtubule-based structure called the ventral disc. Control of attachment is mediated in part by the movement of two regions of the ventral disc that either permit or exclude the passage of fluid under the disc. Several known disc-associated proteins (DAPs) contribute to disc structure and function, but no force-generating protein has been identified among them. We recently identified several Giardia actin (GlActin) interacting proteins at the ventral disc, which could potentially employ actin polymerization for force generation and disc conformational changes. One of these proteins, Disc and Actin Associated Protein 1 (DAAP1), is highly enriched at the two regions of the disc previously shown to be important for fluid flow during attachment. In this study, we investigate the role of both GlActin and DAAP1 in ventral disc morphology and function. We confirmed interaction between GlActin and DAAP1 through coimmunoprecipitation, and used immunofluorescence to localize both proteins throughout the cell cycle and during trophozoite attachment. Similar to other DAPs, the association of DAAP1 with the disc is stable, except during cell division when the disc disassembles. Depletion of GlActin by translation-blocking antisense morpholinos resulted in both impaired attachment and defects in the ventral disc, indicating that GlActin contributes to disc-mediated attachment. Depletion of DAAP1 through CRISPR interference resulted in intact discs but impaired attachment, gating, and flow under the disc. As attachment is essential for infection, elucidation of these and other molecular mediators is a promising area for development of new therapeutics against a ubiquitous parasite.

Storage temperature determines platelet GPVI levels and function in mice and humans.

Platelets are currently stored at room temperature before transfusion to maximize circulation time. This approach has numerous downsides, including limited storage duration, bacterial growth risk, and increased costs. Cold storage could alleviate these problems. However, the functional consequences of cold exposure for platelets are poorly understood. In the present study, we compared the function of cold-stored platelets (CSP) with that of room temperature-stored platelets (RSP) in vitro, in vivo, and posttransfusion. CSP formed larger aggregates under in vitro shear while generating similar contractile forces compared with RSP. We found significantly reduced glycoprotein VI (GPVI) levels after cold exposure of 5 to 7 days. After transfusion into humans, CSP were mostly equivalent to RSP; however, their rate of aggregation in response to the GPVI agonist collagen was significantly lower. In a mouse model of platelet transfusion, we found a significantly lower response rate to the GPVI-dependent agonist convulxin and significantly lower GPVI levels on the surface of transfused platelets after cold storage. In summary, our data support an immediate but short-lived benefit of cold storage and highlight the need for thorough investigations of CSP. This trial was registered at www.clinicaltrials.gov as #NCT03787927.

(De)form and Function: Measuring Cellular Forces with Deformable Materials and Deformable Structures.

The ability for biological cells to produce mechanical forces is important for the development, function, and homeostasis of tissue. The measurement of cellular forces is not a straightforward task because individual cells are microscopic in size and the forces they produce are at the nanonewton scale. Consequently, studies in cell mechanics rely on advanced biomaterials or flexible structures that permit one to infer these forces by the deformation they impart on the material or structure. Herein, the scientific progression on the use of deformable materials and deformable structures to measure cellular forces are reviewed. The findings and insights made possible with these approaches in the field of cell mechanics are summarized.