SELECTIVE INCORPORATION OF ARCHITECTURAL PROTEINS INTO TERMINALLY DIFFERENTIATED MOLLUSCAN GILL CILIA

Incubation of excised gills from the bay scallop Aequipecten irradians with H-3-leucine demonstrates that many ciliary structural proteins c an attain a degree of labeling approaching that previously reported fo r sea urchin or surf clam embryos undergoing ciliary turnover or regen eration. This labeling is not a consequence of any predominant incorpo ration into new cilia at the meristematic growth tips of the gill sinc e tissue regions of varying maturity incorporate label into the same p roteins at similar levels, with the most mature region having the high est incorporation. Sodium dodecyl sulfate-polyacrylamide gel electroph oresis and fluorographic analysis of isolated cilia, separated into de tergent-soluble membrane/matrix and detergent-insoluble 9+2 axoneme fr actions, reveals that 1) tubulin in the membrane/matrix fraction is la beled whereas tubulin in the axoneme is not; 2) no labeled dynein heav y chains are seen in either fraction; 3) the most heavily labeled axon emal components do not appear to any significant extent in the membran e/matrix fraction; and 4) after thermal depolymerization of the microt ubules, nearly all labeled proteins reside in the insoluble ninefold c iliary remnant, the most prominent being tektin A, an integral compone nt of outer doublet microtubules. Further fractionation of the remnant with sarkosyl-urea to produce tektin filaments demonstrates two solub ility classes of tekin A, only the more soluble of which is labeled. V ery similar selective architectural protein labeling patterns have bee n reported for steady-state cilia of sea urchin embryos, and this may indicate a widespread turnover or exchange mechanism characteristic of cilia heretofore considered static. (C) 1996 Wiley-Liss, Inc.