Spindle Scaling and Orientation in Symmetric and Asymmetric Cell Division

During cell division, a microtubule-based macromolecular machine known as mitotic spindle plays an important role to segregate chromosomes to two daughter cells. Molecules locating at cell cortex and spindle equator regulate spindle architecture and orientation. In our study, mitotic spindles in symmetric and asymmetric cell division were investigated. Several human cancer cell lines from lung, breast and colon were chosen as models of symmetric division. By immunofluorescence, we found that the functionally selected highly invasive lung adenocarcinoma cell line, CL1-5, has lengthened steady-state metaphase spindle morphologically distinct from the original line, CL1-0. In addition, our recent study showed that in CL1-5, there was an up-regulation of kinesin-5, a motor protein involved in pole separation and chromosome segregation during mitosis. Therefore, we applied low dose kinesin-5 inhibitor to CL1-5 to reveal the relationship between kinesin-5 and spindle length scaling. As a result, dose-dependent change of spindle length was found. Similarly, an in vivo selected metastatic colon cancer cell line SW620 presented lengthened steady-state metaphase spindle compared to its in situ cell line SW480. These findings entitle spindle length scaling a candidate of cellular marker for metastatic cancer clone, and emphasize alternative benefits of kinesin-5 inhibitor in anti-cancer therapies. On the other hand, we analyzed spindle orientation in asymmetric cell division (ACD) by time-lapse imaging with mouse embryonic stem cells as our model. Microenvironment that promoted asymmetric cell division was built by localized Wnt3a beads. We have established live imaging platform and validated localized Wnt3a signals did orient cell division. We are currently investigating molecules locating at the cell cortex that mediate spindle orientation in asymmetric cell division.