Differential effects of antimitotic agents on the stability and behavior of cytoplasmic and ciliary microtubules

Summary When sea urchin gastrulae are treated with colchicine or hydrostatic pressure the cytoplasmic microtubules disappear, but the ciliary microtubules which make up the ciliary axoneme (9+2) remain. With calcium-free sea water the cytoplasmic microtubules are reduced in number yet the 9+2 complex in the cilia is unaffected. Furthermore during the administration of any of these agents the cilia continue to beat so that functionally as well as morphologically the ciliary microtubules are normal even though the cytoplasmic microtubules are broken down and their presumed function in development is interrupted.Available evidence indicates that these two types of microtubules appear to be made up of similar subunits. Since there are morphological connections between the microtubules of the ciliary axoneme, and since the ciliary microtubules appear to stain more intensely than the cytoplasmic microtubules, we conclude that the ciliary microtubules are stabilized either by the addition of material or through interactions between adjacent tubules or both.Supported by Grant #5T 1-GM-707 from the National Institutes of Health to ProfessorKeith R.Porter.