Studies on the Development of the Sea Urchinstrongylocentrotus DROEBACHIENSIS.III. Embryonic Synthesis of Ciliary Proteins

Cilia were isolated from sea urchin blastula pulse-labeled with 14C-leucine at various time points prior to and during ciliogenesis, the structural components fractionated by SDS-acrylamide gel electrophoresis, and the relative amount of labeled protein determined by autoradiography of gel slices. 2. The two components of the ciliary ATPase dynein are synthesized differentially. The higher molecular weight enzymatic component pre-exists before fertilization; only the lower molecular weight component is synthesized after fertilization and it is made at a constant rate. 3. A number of components with medium and low molecular weights are also synthesized uniformly throughout development. Of these, tubulin alone shows a marked increase in synthesis during late ciliogenesis. This protein is synthesized in three to four-fold excess over that needed for one generation of cilia. All of the others, including dynein, show no significant decrease in specific activity upon regeneration from previously labeled and deciliated embryos. 4. At the initiation of ciliogenesis, at least six minor components appear to arise de novo and only in sufficient amount for one generation of cilia. 5. These data support previous findings that the bulk of ciliary protein is made prior to ciliogenesis and in considerable excess, but suggest further that the morphogenetic process is marked by a "round" of de novo synthesis of minor but critical structural components.