Observation of Photobehavior in Chlamydomonas reinhardtii.

For the survival of the motile phototrophic microorganisms, being under proper light conditions is crucial. Consequently, they show photo-induced behaviors (or photobehavior) and alter their direction of movement in response to light. Typical photobehaviors include photoshock (or photophobic) response and phototaxis. Photoshock is a response to a sudden change in light intensity (e.g., flash illumination), wherein organisms transiently stop moving or move backward. During phototaxis, organisms move toward the light source or in the opposite direction (called positive or negative phototaxis, respectively). The unicellular green alga Chlamydomonas reinhardtii is an excellent organism to study photobehavior because it rapidly changes its swimming pattern by modulating the beating of cilia (a.k.a., flagella) after photoreception. Here, various simple methods are shown to observe photobehaviors in C. reinhardtii. Research on C. reinhardtii's photobehaviors has led to the discovery of common regulatory mechanisms between eukaryotic cilia and channelrhodopsins, which may contribute to a better understanding of ciliopathies and the development of new optogenetics methods.

Cilia Loss and Dynein Assembly Defects in Planaria Lacking an Outer Dynein Arm-Docking Complex Subunit.

The outer dynein arm-docking complex (ODA-DC), which was first identified in the green alga Chlamydomonas reinhardtii, is a protein complex that mediates the binding of axonemal dynein and doublet microtubules. To gain a better understanding of the evolutionary conservation and functional diversity of the ODA-DC, we knocked down a homolog of DC2, a major subunit of the ODA-DC, in the planarian Schmidtea mediterranea. Planaria are carnivorous flatworms that move by beating cilia on their ventral surface against a secreted mucus layer. These organisms have recently been used for cilia research because knockdown of flatworm genes by RNA interference (RNAi) is readily achieved through feeding with double-stranded RNA (dsRNA). Lack of DC2 in S. mediterranea caused several defects in cilia, including low beat frequency, decreased ciliary density, and a reduction in ciliary length. The loss of DC2 function C. reinhardtii mutant oda1 shows slow jerky swimming, but has two flagella of almost normal length. These data suggest that the function of a DC2 homolog in S. mediterranea cilia may be somewhat different from DC2 in C. reinhardtii flagella.