FIGURE 1.

Overview of Stentor coeruleus. (A) Micrograph of a single Stentor cell, attached to the wall of a plastic chamber via its holdfast. (B) Anatomy of Stentor. The oral apparatus (OA) is located at the anterior end of the cell and consists of a membranellar band of cilia, an oral pouch where food is temporarily captured, and a gullet where food is ingested. Inset shows expanded view of the region circled in red, illustrating the ultrastructural organization of the ciliary rows. Each row contains not only pairs of basal bodies, one of which nucleates a cilium, but also a parallel array of microtubule bundles known as Km fibers (Huang and Pitelka, 1973) and, underneath the microtubules, a contractile fiber bundle known as a myoneme, which is composed of centrin-like EF hand calcium binding proteins (Maloney et al., 2005). An additional set of microtubule bundles, known as transverse microtubules, emerge from each basal body pair and extend perpendicularly to the Km fibers toward the adjacent ciliary rows. The spaces in between these rows are filled with blue pigment, giving rise to the blue color seen in (A). The spacing between the ciliary rows shows a circumferential variation, such that the spacing between the rows, and hence the width of the intervening blue stripes as well as the lengths of the transverse microtubule bundles, starts out large at one side of the cell and then gradually decreases as one moves around the circumference, until eventually the narrowest stripes (mostly closely spaced ciliary rows) about the widest stripes (mostly widely separated ciliary rows). This region is known as the locus of stripe contrast, and represents a key site for regeneration of oral structures.