Phenotypic switching to long cilia effected by various proteases: results with Dendraster excentricus and Stronglyocentrotus purpuratus blastulae

Incubation in trypsin effects a phenotypic switch from short to long cilia (greater than 30 micron) in hatched blastulae of the sea urchin, Arbacia punctulata. To determine how trypsin causes such a switch we tested whether the phenomenon was unique to the species, Arbacia, and to the protease, trypsin. With two other echinoderm species, the sand dollar, Dendraster excentricus, and the sea urchin, Strongylocentrotus purpuratus, trypsin incubation increased the percentage of long cilia. During incubation of D. excentricus in trypsin, the percentage of long cilia increased progressively from the normal 10% long cilia of the apical tuft to 45-50% long cilia covering 1/2-3/4 of the embryo. With S. purpuratus blastulae, however, the percentage of long cilia was lower (32-40%) and the results were more variable. Of the additional proteases tested with D. excentricus, elastase was more effective than trypsin in terms of the percentage of long cilia (58%), the mean length, and the broad distribution of lengths formed. Thermolysin was about as effective as trypsin but chymotrypsin was much less so. Thus, increases in ciliary length were not unique to a particular echinoderm species or to incubation in trypsin. The magnitude of the change in length distribution, however, was species- and enzyme-dependent. An extracellular or membrane component with differential susceptibility to various proteases may, therefore, be involved in altering ciliary length.