EXPLORING GRAVITY SENSING MECHANISMS OF CHLAMYDOMONAS REINHARDTII
Tohoku University, Japan
Chlamydomonas reinhardtii is a model organism of eukaryotic flagella. It has a nearly spherical cell body and two anterior flagella, and swims like human breaststroke with those flagella. Although it is a unicellular green alga that looks very different from humans, the basic “9+2” structure of its flagella is the same as that of human cilia and flagella observed in trachea, brain ventricles, oviducts and sperm, generating important functional flows in our body. Thus, investigating the mechanisms of motility and behavior of this tiny organism could contribute to biomedical engineering as well as basic biology. In addition, Chlamydomonas lives most of its life cycle as haploid: in normal conditions, it reproduces asexually, just divides and makes a genetically homogenous population. Because it is a haploid, genetic defects are straightforwardly reflected to the phenotype. Furthermore, Chlamydomonas starts sexual reproduction under a certain experimental environment, thus crossing between the given strains is possible. These characteristics make it easy to do genetic analysis: Chlamydomonas is an excellent model system to investigate flagellar structures and functions.
Like other protists, Chlamydomonas senses the environmental stimuli such as light, mechanical shock and gravity, and shows behavioral responses. Here, I explore gravitactic behavior of C. reinhardtii. Yoshimura et al. (2003, Plant Cell Physiol.) isolated 2 gravitactic mutant strains called gtx1 and gtx2, that showed weaker negative gravitaxis than the wild type but were normal in most of the other motility phenotypes. Initial reassessment showed some contradictory results to the original description. The relationship between gtx1 and gtx2 is being investigated using genetic and physiological methods.