CHLORAL HYDRATE ALTERS THE ORGANIZATION OF THE CILIARY BASAL APPARATUS AND CELL ORGANELLES IN SEA-URCHIN EMBRYOS

The mitotic inhibitor, chloral hydrate, induces ciliary loss in the ea rly embryo phase of Lytechinus pictus. It causes a breakdown of cilia at the junction of the cilium and the basal body known as the basal pl ate. This leaves the plasma membrane temporarily unsealed. The basal a pparatus accessory structures, consisting of the basal body, basal foo t, basal foot cap, striated side arm, and striated rootlet, are either misaligned or disintegrated by treatment with chloral hydrate. Furthe rmore, microtubules which are associated with the basal apparatus are disassembled. Mitochondria accumulate at the base of cilia - underneat h the plasma membrane - and show alterations in their structural organ ization, The accumulation of mitochondria is observed in 40% of all el ectron micrograph sections while 60% show the areas mostly devoid of m itochondria. The microvilli surrounding a cilium and striated rootlet remain intact in the presence of chloral hydrate. These results sugges t that deciliation in early sea urchin embryos by chloral hydrate is c aused by combined effects on the ciliary membrane and on microtubules in the cilia. Furthermore, it is suggested that chloral hydrate can se rve as a tool to explore the cytoskeletal mechanisms that are involved in cilia motility in the developing sea urchin embryo.