Ciliary elongation in blastulae of Arbacia punctulata induced by trypsin

Hatched sea urchin blastulae, which have primarily short 25-μm cilia except for some long 40-to 70-μm cilia at the apical tuft, were induced to form long (40- to 70-μm) cilia around most of their circumference when treated with trypsin (0.008–0.1%) or concanavalin A. Other animalizing agents did not induce the formation of long cilia when applied to the normal blastulae. The formation of long cilia by trypsin was both time and concentration dependent. The long cilia first appeared around the apical tuft after 6–8 hr in trypsin (21°C), and by 18–22 hr most of the blastula was covered with the long cilia. Length distribution studies on cilia isolated at various times showed that the percentage of long cilia increased from approximately 10% in the normal blastula to over 66% in the 22-hr trypsin-treated embryo, and indicated that the long cilia formed by the elongation of the original short cilia. Only the blastulae and gastrulae could be induced to form long cilia; the prisms and plutei could not. Once development was inhibited by the trypsin and the first long cilia appeared, the trypsin effect could not be reversed. When blastulae with long cilia were removed from the trypsin for 10 hr, the cilia remained long; when the long cilia were detached, the blastulae regenerated long cilia in the absence of trypsin. The induced long cilia moved poorly, similar to the long, apical tuft cilia of normal embryos. The formation of long cilia by trypsin treatment of sea urchin blastulae provides a model system for studying the mechanisms of ciliary length control.