Date of Award
Doctor of Philosophy (PhD)
Motile cilia and flagella are ancient organelles that eukaryotic organisms today still rely on to thrive in their natural environment. Not surprisingly, accumulated evidence has shown that the intricate motility machinery, the microtubule-based axoneme, is evolutionarily conserved down to the molecular level. This notion is epitomized by the signature axonemal complex, the radial spoke (RS). The RS is part of a control center conferring the high frequency and tightly regulated movement. Key RS proteins discovered in biflagellate green alga, Chlamydomonas reinhardtii, are also generated by nearly all ciliated organisms, including Homo sapiens. Among them are two subunits from primordial protein families, nucleoside diphosphate kinase (NDK) and heat shock protein (HSP) 40, that are positioned at a critical juncture where two arms merge into a singular stalk in the Y-shaped complex. While it is well accepted that NDKs and HSP40s maintain nucleotide homeostasis and assist HSP70 chaperone in protein folding respectively, these actions fail to explain observations in myriads of vital cellular processes. Using the experimental approaches possible in the biflagellate green algae, genetics in particular, this dissertation discovers non-canonical applications of these two spoke proteins in the assembly and motility of the RS and entire flagellum. The versatility sheds light on the canonical mechanisms, the diverse processes adopting the non-canonical mechanisms, and their preservation since their conscription perhaps by the cell ancestral to all eukaryotes.