Effect of cellular rearrangement time delays on the rheology of vertex models for confluent tissues

Large-scale tissue deformation during biological processes such as morphogenesis requires cellular rearrangements. The simplest rearrangement in confluent cellular monolayers involves neighbor exchanges among four cells, called a T1 transition, in analogy to foams. But unlike foams, cells must execute a sequence of molecular processes, such as endocytosis of adhesion molecules, to complete a T1 transition. Such processes could take a long time compared to other timescales in the tissue. In this work, we incorporate this idea by augmenting vertex models to require a fixed, finite time for T1 transitions, which we call the "T1 delay time". We study how variations in T1 delay time affect tissue mechanics, by quantifying the relaxation time of tissues in the presence of T1 delays and comparing that to the cell-shape based timescale that characterizes fluidity in the absence of any T1 delays. We show that the molecular-scale T1 delay timescale dominates over the cell shape-scale collective response timescale when the T1 delay time is the larger of the two. We extend this analysis to tissues that become anisotropic under convergent extension, finding similar results. Moreover, we find that increasing the T1 delay time increases the percentage of higher-fold coordinated vertices and rosettes, and decreases the overall number of successful T1s, contributing to a more elastic-like -- and less fluid-like -- tissue response. Our work suggests that molecular mechanisms that act as a brake on T1 transitions could stiffen global tissue mechanics and enhance rosette formation during morphogenesis

Preparing STEM Teachers for Integration of NGSS: a Summer Workshop Development

The increasing emphasis on Science, Technology, Engineering and Mathematics (STEM) education in United States and across the world created the demand for STEM education to start as early as elementary school. Especially in the past decade, the demand for middle schools and high schools to increase the involvement of the STEM components in their curriculum has been on the rise. The Next Generation Science Standards (NGSS)(http://www.nextgenscience.org/) are testimonial to this demand and need. With the fast-pace the NGSS are being adopted by different states, the expectations from science, engineering, and technology teachers to develop and design their courses to reflect the new standards and meet the updated goals increased. To support teachers with the necessary resources and training, a Summer STEM training program and a set of STEM training modules have been developed by a 4-year accredited State College. This paper provides an overview of the STEM initiatives and a step-by-step approach of the design and development of the STEM modules to train K-12 teachers

Tissue flow induces cell shape changes during organogenesis

In embryonic development, programmed cell shape changes are essential for building functional organs, but in many cases the mechanisms that precisely regulate these changes remain unknown. We propose that fluid-like drag forces generated by the motion of an organ through surrounding tissue could generate changes to its structure that are important for its function. To test this hypothesis, we study the zebrafish left-right organizer, Kupffer's vesicle (KV), using experiments and mathematical modeling. During development, monociliated cells that comprise the KV undergo region-specific shape changes along the anterior-posterior axis that are critical for KV function: anterior cells become long and thin, while posterior cells become short and squat. Here, we develop a mathematical vertex-like model for cell shapes, which incorporates both tissue rheology and cell motility, and constrain the model parameters using previously published rheological data for the zebrafish tailbud [Serwane et al.] as well as our own measurements of the KV speed. We find that drag forces due to dynamics of cells surrounding the KV could be sufficient to drive KV cell shape changes during KV development. More broadly, these results suggest that cell shape changes could be driven by dynamic forces not typically considered in models or experiments

Anisotropy links cell shapes to tissue flow during convergent extension

Within developing embryos, tissues flow and reorganize dramatically on timescales as short as minutes. This includes epithelial tissues, which often narrow and elongate in convergent extension movements due to anisotropies in external forces or in internal cell-generated forces. However, the mechanisms that allow or prevent tissue reorganization, especially in the presence of strongly anisotropic forces, remain unclear. We study this question in the converging and extending Drosophila germband epithelium, which displays planar polarized myosin II and experiences anisotropic forces from neighboring tissues, and we show that in contrast to isotropic tissues, cell shape alone is not sufficient to predict the onset of rapid cell rearrangement. From theoretical considerations and vertex model simulations, we predict that in anisotropic tissues two experimentally accessible metrics of cell patterns, the cell shape index and a cell alignment index, are required to determine whether an anisotropic tissue is in a solid-like or fluid-like state. We show that changes in cell shape and alignment over time in the Drosophila germband predict the onset of rapid cell rearrangement in both wild-type and snail twist mutant embryos, where our theoretical prediction is further improved when we also account for cell packing disorder. These findings suggest that convergent extension is associated with a transition to more fluid-like tissue behavior, which may help accommodate tissue shape changes during rapid developmental events

The role of port operations in the development of cruise tourism: The case of port of Antalya

Cruise tourism, which is evaluated within marine tourism, has significant environmental, economic, and socio-cultural impacts on visited ports. Cruise tourism is an activity that provides economic income to the harbors and creates new jobs. The cruise tourism has an increasing demand in the recent years because cruise ship visitors both have an opportunity to see many countries and cities in a short time and have a vacation on a luxury ship, which has a comfort standard like a holiday village. With her historical, cultural and natural attractions, Turkey is located in very strategic and convenient point and also Turkey is so close to destinations that cruise ships prefer to visit in the Mediterranean Basin. In 2014, approximately 22 million tourist travelled with cruise ships in the World and 1.8 million cruise passengers came to Turkey. The aim of this study is evaluate the development of cruise tourism in Turkey in terms of port operations. In previous studies it has focused on the development of cruise tourism but has not been evaluated in terms of port operations perspective. Semi-structured interview technique was used in the study and interviewed with General Manager of Antalya Global Ports Holding, which is one of Turkey’s most important port operations. Turkey and in the World cruise tourism is compared and has been reached important information about the development of cruise tourism

Association of SNAP-25 gene Ddel and Mnll Polymorphisms with adult attention deficit hyperactivity disorder

Objective The synaptosomal-associated protein of 25 kDa (SNAP-25) gene is a presynaptic plasma membrane protein and an integral component of the vesicle docking and fusion machinery mediating secretion of neurotransmitters. Previously, several studies reported association between SNAP-25 and attention deficit hyperactivity disorder (ADHD). We investigated whether these SNAP-25 polymorphisms (MnlI T/G and DdelI T/C) were also associated with ADHD in the Turkish population. Methods: Our study comprised unrelated 139 subjects who met DSM-IV criteria for ADHD and 73 controls and all were of Turkish origin. Genetic analyses were performed and patients were evaluated with Wender-Utah Rating Scale and Adult ADD/ADHD DSM IV-Based Diagnostic Screening and Rating Scale. Results: SNAP-25 DdelI polymorphism was not associated with ADHD but there was a statistically significant difference between ADHD patients and controls for SNAP-25 MnlI polymorphism. For SNAP-25 MnlI polymorphism patients with G/G genotype of the SNAP-25 gene MnlI polymorphism had higher Wender-Utah scores and higher scores in the 1st and 3rd parts of adult ADD/ADHD Scale. Conclusion: We detected a significant association of the MnlI polymorphism in our ADHD sample which was similar to previous findings. Our study also revealed that SNAP-25 MnlI polymorphism was also associated with symptom severity of ADHD. This study is also, the first report on the association of SNAP-25 with ADHD in the Turkish population. © 2014 Korean Neuropsychiatric Association