MESSENGER-RNAS FOR MICROTUBULE PROTEINS ARE SPECIFICALLY COLOCALIZED DURING THE SEQUENTIAL FORMATION OF BASAL BODY, FLAGELLA, AND CYTOSKELETAL MICROTUBULES IN THE DIFFERENTIATION OF NAEGLERIA-GRUBERI

We have examined the distribution of four mRNAs-alpha-tubulin, beta-tu bulin, flagellar calmodulin, and Class I mRNA-during differentiation o f Naegleria gruberi amebas into flagellates by in situ hybridization. Three of the four mRNAs-alpha-tubulin, beta-tubulin, and Class I mRNA- began to be colocalized at the periphery of the cells as soon as trans cription of the respective genes was activated and before any microtub ular structures were observable. At 70 min after the initiation of dif ferentiation, these mRNAs were relocalized to the base of the growing flagella, adjacent to the basal bodies and microtubule organizing cent er for the cytoskeletal microtubules. Within an additional 15 min, the mRNAs were translocated to the posterior of the flagellated cells, an d by the end of differentiation (120 min), very low levels of the mRNA s were observed. Cytochalasin D inhibited stage-specific localization of the mRNAs, demonstrating that RNA localization was actin dependent, Since cytochalasin D also blocked differentiation, this raises the po ssibility that actin-dependent RNA movement is an essential process fo r differentiation.