Speaker: Reza Farhadifar, Ph.D., Research Scientist, Biophysical Modeling
Topic: How cells regulate the size of their structures
The size of intracellular structures such as the nucleus, Golgi apparatus, and mitotic spindle scale with cell size, i.e., larger cells, tend to have a larger nucleus and spindles. The mechanisms that regulate the size of intracellular structures and their scaling with cell size are poorly understood. I will present a mechanistic explanation for variations in the dynamics, positioning, and scaling of the first mitotic spindle in nematodes. I will present laser ablation experiments, which allowed us to directly assess the nature of forces acting on the spindle by severing different populations of microtubules. These experiments showed that spindle motion results from astral microtubules pulling from many directions, with movement ceasing only when those pulling forces are in balance. We constructed a model of cortical pulling forces, based on known biochemical properties of microtubules and molecular motors. We found that this model reproduces the dynamics of spindle positioning and elongation, spindle final size, and its scaling with cell length in C. elegans. I will show that this model also accounts for variations in all the spindle traits we studied here, across nematode species spanning over 100 million years of evolution.