We here at the Langlais Lab have become highly interested in the movement of proteins that track along the growing "plus end" of the microtubule. This subset of the microtuble-associated protein ("MAP") family is referred to as the "+TIPs" ("plus-end interacting proteins"). In the video above, green is CLASP2, our favorite +TIP, and magenta (NOT purple, i've been berated extensively on this) is fluorescently-labeled alpha-tubulin, which represents microtubules. In these 3T3-L1 fibroblasts, you can see in the real time video the movement of CLASP2 relative to the microtubule, and how CLASP2 sticks to the plus-ends. Make sure to click on the "Enter full screen" button on the bottom right corner of the video to make the video nice and big.
In our 2017 MCP paper on characterizing the CLASP2 interactome in 3T3-L1 adipocytes, we discovered a link between CLASP2 and G2L1. G2L1 is pretty interesting because not only is it a +TIP, it also binds actin. We love GLUT4 trafficking here in the Langlais Lab, and G2L1 immediately caught our interest. GLUT4 has been proposed to switch from trafficking along microtubules to actin at some point along its voyage, so maybe G2L1 is part of that mechanism. In our 2019 MCP paper, we were able to reciprocally confirm the presence of CLASP2 in G2L1 interactomes and further strengthen these findings with the live-cell discovery that CLASP2 (green) and G2L1 (magenta) colocalize at microtubule plus-ends (click on the "Enter full screen" button on the video above).
We had discovered that knocking down CLASP2 protein expression in 3T3-L1 adipocytes negatively impacts insulin-stimulated GLUT4 trafficking and glucose uptake, implicating CLASP2 in insulin action. Our next stop was to asses the temporospatial effect of insulin on CLASP2 dynamics. Sure enough, we discovered that insulin causes microtubules with CLASP2 at their tips to grow slower. We also found out that insulin stimulates CLASP2 to switch from exclusive plus-end tracking to “trailing” behind the growing tip of the microtubule (the single green video above), a finding that held true for G2L1 as well (the single magenta video above). When co-expressed together, CLASP2 (green) and G2L1 (magenta) co-track and also co-trail after insulin stimulation (see the three videos side-by-side above). We published all this stuff in the 2019 MCP paper. Don't forget to click on the "Enter full screen" button to make those videos big.