A search for in vivo factors in regulation of microtubule assembly

Abstract

MICROTUBULES are abundant in eukaryotic cells where they assume various functions¹, some of which seem to be at a purely structural level, such as maintenance of cell shape and axonal elongation, whereas others are involved in more dynamic processes, such as mitosis, meiosis, secretion and axonal transport. At least two distinct protein factors of different molecular weight have been suggested^2–5 to regulate microtubule assembly. The uniqueness of their role is not unequivocally established because microtubules have also been obtained in the absence of these protein factors, at high magnesium ion concentrations⁶, in the presence of polycations⁷ or glycerol¹¹. To correlate better the results obtained in vitro with the mechanism operating in vivo, we have studied the assembly of microtubules in extracts prepared from developing rat brain, differentiating mouse neuroblastoma cells and in chicken sensory ganglia, which may facilitate detection of a factor which induces self-assembly in vivo. We conclude that the high molecular weight protein is seemingly not required for the in vivo assembly of microtubules.