The Dynamics of Aerotaxis in a Simple Eukaryotic Model

In aerobic organisms, oxygen is essential for efficient energy production, and it acts as the last acceptor of the mitochondrial electron transport chain and as regulator of gene expression. However, excessive oxygen can lead to production of deleterious reactive oxygen species. Therefore, the directed migration of single cells or cell clumps from hypoxic areas toward a region of optimal oxygen concentration, named aerotaxis, can be considered an adaptive mechanism that plays a major role in biological and pathological processes. One relevant example is the development of O2 gradients when tumors grow beyond their vascular supply, leading frequently to metastasis. In higher eukaryotic organisms, aerotaxis has only recently begun to be explored, but genetically amenable model organisms suitable to dissect this process remain an unmet need. In this regard, we sought to assess whether Dictyostelium cells, which are an established model for chemotaxis and other motility processes, could sense oxygen gradients and move directionally in their response. By assessing different physical parameters, our findings indicate that both growing and starving Dictyostelium cells under hypoxic conditions migrate directionally toward regions of higher O2 concentration. This migration is characterized by a specific pattern of cell arrangement. A thickened circular front of high cell density (corona) forms in the cell cluster and persistently moves following the oxygen gradient. Cells in the colony center, where hypoxia is more severe, are less motile and display a rounded shape. Aggregation-competent cells forming streams by chemotaxis, when confined under hypoxic conditions, undergo stream or aggregate fragmentation, giving rise to multiple small loose aggregates that coordinately move toward regions of higher O2 concentration. By testing a panel of mutants defective in chemotactic signaling, and a catalase-deficient strain, we found that the latter and the pkbR1null exhibited altered migration patterns. Our results suggest that in Dictyostelium, like in mammalian cells, an intracellular accumulation of hydrogen peroxide favors the migration toward optimal oxygen concentration. Furthermore, differently from chemotaxis, this oxygen-driven migration is a G protein-independent process

SrfB, a member of the Serum Response factor family of transcription factors, regulates starvation response and early development in Dictyostelium

The Serum Response Factor (SRF) is an important regulator of cell proliferation and differentiation. Dictyostelium discoideum srfB gene codes for an SRF homologue and is expressed in vegetative cells and during development under the control of three alternative promoters, which show different cell-type specific patterns of expression. The two more proximal promoters directed gene transcription in prestalk AB, stalk and lower-cup cells. The generation of a strain where the srfB gene has been interrupted (srfB(−)) has shown that this gene is required for regulation of actin–cytoskeleton-related functions, such as cytokinesis and macropinocytosis. The mutant failed to develop well in suspension, but could be rescued by cAMP pulsing, suggesting a defect in cAMP signaling. srfB(−) cells showed impaired chemotaxis to cAMP and defective lateral pseudopodium inhibition. Nevertheless, srfB(−) cells aggregated on agar plates and nitrocellulose filters 2 h earlier than wild type cells, and completed development, showing an increased tendency to form slug structures. Analysis of wild type and srfB(−) strains detected significant differences in the regulation of gene expression upon starvation. Genes coding for lysosomal and ribosomal proteins, developmentally-regulated genes, and some genes coding for proteins involved in cytoskeleton regulation were deregulated during the first stages of development

Functional characterization of iron transporter from Dictyostelium discoideum as a model of cellular iron homeostasis

Iron plays a central role in a large number of essential cellular functions but it is also potentially toxic being able to generate reactive oxygen species. The social amoeba Dictyostelium discoideum possesses several iron genes with the exception of transferrin, ferritin and TFR (Bozzaro et al., 2013; Peracino et al., 2013) and represents a model for the study of cellular iron homeostasis showing subcellular localization of iron transporters resembling that of macrophages. In particular, D. discoideum expresses the ortholog of Nramp1 transporter in phago-lysosomes and that of Nramp2 in the contractile vacuole. To better understand the function of dd Nramp1, the protein was expressed in Xenopus laevis oocytes by cRNA injection and functionally tested by radiochemical and electrophysiological techniques. To increase the surface localization of dd Nramp1, its N and C termini were replaced with the corresponding regions of the murine DMT1, which shows a high level of expression in the membrane of X. laevis oocytes (Gunshin et al., 1997). Dd Nramp1 is an electrogenic proton-dependent divalent metal ion transporter with a cation selectivity comparable to that of the murine DMT1 (Illing et al., 2012). It transports ferrous but not ferric iron and it is partially inhibited by Na+

Studio longitudinale sul benessere e le attitudini degli Studenti di Medicina e Chirurgia. Primi risultati della fase 1: Le caratteristiche degli studenti selezionati

We present the first results of a longitudinal study for the recognition and assessment of non-cognitive aspects of the candidates access to medicine course, and throughout the course. This study considered 8 CLMs equally distributed throughout the country and 980 students enrolled in the first year, in the academic year 2013-2014. Preliminary results obtained from the analysis of the questionnaire used in the research show that students expect a profession characterized by the aid for patients and socially useful, while they do not expect a low pay as well as a work activity risky for health. Students are motivated to the academic course mainly by the desire to care for others, while variously opportunistic aspects are much less relevant. Students show high capacity of self-regulation, a high level of empathy in its both aspects of propensity to engagement with others in their difficult moments, as well as of tendency to spontaneously take the perspective of others, while they are able to maintain a goal directed behavior even in the presence of suffering others. These students are basically satisfied, they show a confident and positive attitude towards life and a substantial psychological health. However, it is possible to identify a sub-group of students showing signals of psychological fragility who must be carefully monitored: their profiles will be analyzed in more detail, through in-depth interviews scheduled for the third/fourth year as part of faculties counselling services

Clinical outcomes, MRI evaluation and predictive factors of indirect decompression with lateral transpsoas approach for lumbar interbody fusion: a multicenter experience

Introduction: Evaluating the effects of indirect decompression obtained through lateral lumbar interbody fusion (LLIF) by clinical improvements and radiological parameters on MRI scans. Identifying predictors of better decompression and clinical outcome. Materials and methods: From 2016 to 2019, patients who underwent single- or double-level indirect decompression LLIF were consecutively reviewed. Radiological signs of indirect decompression were evaluated in preoperative and follow-up MRI studies and were subsequently correlated to clinical data, expressed as axial/radicular pain (VAS back/leg), index of disability (Oswestry Disability Index) and clinical severity of lumbar stenosis (Swiss Spinal Stenosis Questionnaire). Results: 72 patients were enrolled. The mean follow-up was 24 months. Differences in vertebral canal area (p < 0.001), height of the foramina (p < 0.001), thickness of the yellow ligament (p = 0.001) and anterior height of the interbody space (p = 0.02) were observed. Older age (p = 0.042), presence of spondylolisthesis (p = 0.042), presence of intra-articular facet effusion (p = 0.003) and posterior height of the implanted cage (p = 0.020) positively affected the increase of the canal area. Change in root canal area (p < 0.001), height of the implanted cage (p = 0.020) and younger age (p = 0.035) were predictive factors of root pain relief, while increased vertebral canal area (p = 0.020) and height of the interbody fusion cage (p = 0.023) positively affected the severity of clinical stenosis. Conclusions: LLIF indirect decompression showed both clinical and radiological improvements. Presence and degree of spondylolisthesis, presence of intra-articular facet effusion, age of the patient and height of the cage were predictive factors of major clinical improvements