There were a a lot of talks and posters on this session and I obviously cant cover all of them, but here are a few highlights!

The Mechanobiology subgroup is growing over the years. It ranged from cell clusters to single cells, from engineering techniques to mathematical modeling and more… It was an action packed day and here are some of the highlights.

Vinculin catch bond is directional! Alex Dunn’s lab has now done neat experiments to show that Vinculin forms a catch bond very neatly in the direction of actin flow. This allows the binding to the rearward flowing actin and slowing it down.

Another neat talk by Kristian Franze (who is also the president elect for 2018 – Congratulations ☺) showed their interesting work on how neurons migrate through repellant gradients. They show that during development, when neurons enervate the area of the brain, they do so even though there is a chemical repellant present there. Using both imaging and biophysical manipulations invitro and invivo (AFM cantilever) they show that the neurons require a particular range stiffness to migrate and reach their final destination. This led to interesting speculations about the reason for poor neuronal regeneration in scar tissue in the brain, which is actually stiffened by the glial cells.

There were two talks talking answering questions of cell division - one dealing with kinetochores in chromosome segregation and another about the acto-myosin contractile ring. Mary Elting’s work answered questions about where are the spindles anchored or rather where are the K fibers, just at the tip or throughout the entire spindle during chromosome segregation? They used Ptk2 cells – as these cells have very few chromosomes hence easier to work with. She cut the spindles at different distances from the chromosome and measured chromosome recoil. These experiments suggest that the K fibers are anchored almost throughout the length of the spindle.

Binh An Truong Quang from Ewa Paluch's lab, took to the theme of acto-myosin ring contraction. The major question was how does the ring contract. Using double-labeled myosin they devised a nice way to measure the angle of myosin with respect to actin. They show that as the tension in the ring increases about 2 fold during contraction, they myosin angle changes with respect to the actin, explaining the increase in tension.

Lisa Manning gave a great talk no their modeling studies, where the magic number was 3.81. What is 3.81, that's the ratio of perimeter:square root of area (model parameter). Of densely packed cells. What does this tell us, that by just measuring these parameters, one can actually tell if the cells are stationary or fluid like. This was an interesting problem from the physics perspective as cells have no gaps so how can they flow – by interacting with their neighbours and it turns out that these interactions can change the model parameter. Hence just by looking at the value of the model parameter one can easily determine the state of cells. Further, she had developed a very a neat phase diagram where cell shapes were determined as a function of stiffness and what would happen in a cell sheet.

Otter Campas has developed a very nice method to forces in an intact tissue. They use magnetized oil droplets roughly 3 times the size of the cell and insert it in the tissue (they were focusing on developing zebra fish). Using this they can apply pair forces to the cells and measure local strain maps without perturbing morphogenetic movements.

Switching gears here, I went to attend Miriam Goodman’s talk, as I would be co-chairing the session with her the next day. It was amazing, where they set out to understand how worms respond to touch. The assay they use is to poke the worm with an eyebrow hair. They show that the force generated by this, though variable between humans - is enough to saturate the response of the worm (2pN). This is primarily mediated by MEC4 (ENAC Channel proteins). Worms expressed these channels in the epidermis near the skin and those lacking these channels are touch dead. Further, they can make stiff (using glue) or soft worms (dissecting the gut) and measure how the touch response is modulated.

Great! That was Saturday, a relatively short day as it ended by 6pm.. .And then it was Mardi Gras festivities. Of course the political satire themed parade was on everyone’s agenda! What Can I say it was fun! Lots of people wrote about that, but here is what I found – A monument on the banks of Mississippi to guess what? That's right! Immigrants! Woah! Enjoy the big and easy :)

Rishita Changede