HETEROTRIMERIC KINESIN-II IS REQUIRED FOR THE ASSEMBLY OF MOTILE 9-URCHIN EMBRYOS(2 CILIARY AXONEMES ON SEA)

Heterotrimeric kinesin-II is a plus end-directed microtubule (MT) moto r protein consisting of distinct heterodimerized motor subunits associ ated with an accessory subunit. To probe the intracellular transport f unctions of kinesin-II, we microinjected fertilized sea urchin eggs wi th an anti-kinesin-II monoclonal antibody, and we observed a dramatic inhibition of ciliogenesis at the blastula stage characterized by the assembly of short, paralyzed, 9+0 ciliary axonemes that lack central p air MTs. Control embryos show no such defect and form swimming blastul ae with normal, motile, 9+2 cilia that contain kinesin-II as detected by Western blotting. Injection of anti-kinesin-II into one blastomere of a two-cell embryo leads to the development of chimeric blastulae co vered on one side with short, paralyzed cilia, and on the other with n ormal, beating cilia. We observed a unimodal length distribution of sh ort cilia on anti-kinesin-II-injected embryos corresponding to the fir st mode of the trimodal distribution of ciliary lengths observed for c ontrol embryos. This short mode may represent a default ciliary assemb ly intermediate. We hypothesize that kinesin-II functions during cilio genesis to deliver ciliary components that are required for elongation of the assembly intermediate and for formation of stable central pair MTs. Thus, kinesin-II plays a critical role in embryonic development by supporting the maturation of nascent cilia to generate long motile organelles capable of producing the propulsive forces required for swi mming and feeding.