Do you \u3cem\u3ereally\u3c/em\u3e love me?: An experimental investigation of reassurance seeking and interpersonal rejection

The authors conducted an experiment to test the interpersonal model of depression (Coyne, 1976), and specifically the link between excessive reassurance seeking (ERS) and rejection. The present study involved college-aged romantic couples. Some participants were then manipulated into perceiving that their partner was seeking reassurance from them. Results support the main tenets of Coyne’s (1976) theory. Participants reported increased frustration and reduced felt closeness to dysphoric partners when they were led to believe that their partners were engaging in ERS. Effects on frustration were moderated by partners’ depression, while effects on felt closeness were partially mediated by frustration, yielding a mediated moderation model. Alternative explanations were not supported. Clinical and theoretical implications are discussed

ASSEMBLY OF SEPTINS ON CURVED MEMBRANES: FROM SINGLE MOLECULES TO HIGHER-ORDER STRUCTURES

The septin cytoskeleton is a highly conserved family of filament-forming, GTP-binding proteins found in yeast through humans. Septins were first discovered during the cell division cycle (cdc) mutagenesis screens in budding yeast, where they were shown to be essential for cytokinesis. Despite their discovery in the 1970’s, comparatively little is known about septin structure, function, and mechanisms of assembly when compared to other cytoskeletal polymers such as actin, microtubules, and intermediate filaments. In cells, septins are often found associated on membranes, both flat and curved, where they function in cell cycle progression, cell migration, and degradation of invading microorganisms into host cells. Septin assembly onto membranes begins with the binding of short nanometer-sized rod complexes which diffuse and anneal to form filaments and higher-order structures including filament pairs, rings, and gauzes. Despite our current knowledge, it is unclear how septins associate with membranes, especially in a geometry-dependent manner. Moreover, it is unclear if/how the step-wise septin assembly process is sensitive to changes in membrane shape. In this dissertation we find that septins contain a highly conserved amphipathic helix, a structural motif essential for preferential assembly of septins onto curved membranes. Interestingly, we find that single septin octamers are capable of sensing membrane curvature on the nanometer scale, however, this does not explain the micrometer-scale curvature preference of septins able to polymerize. We find that septins must polymerize to stably associate with membranes and that septin filaments are longer on micrometer-scale membrane curvatures. Collectively, our data shows that curvature sensing by septins operates on multiple length scales, at the level of individual protein domains through filament formation.Doctor of Philosoph

An amphipathic helix enables septins to sense micrometer-scale membrane curvature

© The Authors, 2019. This article is distributed under the terms of the Creative Commons Attribution-Noncommercial-Share Alike 4.0 International License. The definitive version was published in Journal of Cell Biology (2019), doi:10.1083/jcb.201807211.Cell shape is well described by membrane curvature. Septins are filament-forming, GTP-binding proteins that assemble on positive, micrometer-scale curvatures. Here, we examine the molecular basis of curvature sensing by septins. We show that differences in affinity and the number of binding sites drive curvature-specific adsorption of septins. Moreover, we find septin assembly onto curved membranes is cooperative and show that geometry influences higher-order arrangement of septin filaments. Although septins must form polymers to stay associated with membranes, septin filaments do not have to span micrometers in length to sense curvature, as we find that single-septin complexes have curvature-dependent association rates. We trace this ability to an amphipathic helix (AH) located on the C-terminus of Cdc12. The AH domain is necessary and sufficient for curvature sensing both in vitro and in vivo. These data show that curvature sensing by septins operates at much smaller length scales than the micrometer curvatures being detected.We thank the Gladfelter laboratory and Danny Lew for useful discussions, Matthias Garten for ideas in setting up the rod assay, and the University of North Carolina EM facility (Victoria Madden and Kristen White) for support with scanning electron microscope. This work was supported by a Howard Hughes Medical Institute Faculty Scholars award to A.S. Gladfelter, and K.S. Cannon was supported in part by a grant from the National Institute of General Medical Sciences under award T32 GM119999.2019-07-0

The hierarchical assembly of septins revealed by high-speed AFM

© The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Jiao, F., Cannon, K. S., Lin, Y. C., Gladfelter, A. S., & Scheuring, S. The hierarchical assembly of septins revealed by high-speed AFM. Nature Communications, 11(1), (2020): 5062, doi:10.1038/s41467-020-18778-x.Septins are GTP-binding proteins involved in diverse cellular processes including division and membrane remodeling. Septins form linear, palindromic heteromeric complexes that can assemble in filaments and higher-order structures. Structural studies revealed various septin architectures, but questions concerning assembly-dynamics and -pathways persist. Here we used high-speed atomic force microscopy (HS-AFM) and kinetic modeling which allowed us to determine that septin filament assembly was a diffusion-driven process, while formation of higher-order structures was complex and involved self-templating. Slightly acidic pH and increased monovalent ion concentrations favor filament-assembly, -alignment and -pairing. Filament-alignment and -pairing further favored diffusion-driven assembly. Pairing is mediated by the septin N-termini face, and may occur symmetrically or staggered, likely important for the formation of higher-order structures of different shapes. Multilayered structures are templated by the morphology of the underlying layers. The septin C-termini face, namely the C-terminal extension of Cdc12, may be involved in membrane binding.We thank J. Thorner for the generous gift of the CTE mutant plasmids. K.S.C. was supported in part by a grant from NIGMS under award T32 GM119999 and A.S.G., F.J. and S.S. were supported by NIH RO1 GM130934

Increased risk for other cancers in individuals with Ewing sarcoma and their relatives.

BackgroundThere are few reports of the association of other cancers with Ewing sarcoma in patients and their relatives. We use a resource combining statewide genealogy and cancer reporting to provide unbiased risks.MethodsUsing a combined genealogy of 2.3 million Utah individuals and the Utah Cancer Registry (UCR), relative risks (RRs) for cancers of other sites were estimated in 143 Ewing sarcoma patients using a Cox proportional hazards model with matched controls; however, risks in relatives were estimated using internal cohort-specific cancer rates in first-, second-, and third-degree relatives.ResultsCancers of three sites (breast, brain, complex genotype/karyotype sarcoma) were observed in excess in Ewing sarcoma patients. No Ewing sarcoma patients were identified among first-, second-, or third-degree relatives of Ewing sarcoma patients. Significantly increased risk for brain, lung/bronchus, female genital, and prostate cancer was observed in first-degree relatives. Significantly increased risks were observed in second-degree relatives for breast cancer, nonmelanoma eye cancer, malignant peripheral nerve sheath cancer, non-Hodgkin lymphoma, and translocation sarcomas. Significantly increased risks for stomach cancer, prostate cancer, and acute lymphocytic leukemia were observed in third-degree relatives.ConclusionsThis analysis of risk for cancer among Ewing sarcoma patients and their relatives indicates evidence for some increased cancer predisposition in this population which can be used to individualize consideration of potential treatment of patients and screening of patients and relatives