Algal Ciliary Motility

Abstract

The microtubule‐based cilium (also known as a flagellum) extends from the surface of most eukaryotic cells. This long, slender organelle is biochemically complex and is conserved in many eukaryotic organisms. The unicellular alga, Chlamydomonas reinhardtii, serves as a tractable organism for studying the assembly and function of cilia. Cilia provide locomotion and environmental sensing. To produce motility, specialised molecular motors called outer and inner dynein arms generate force to produce waveform. These motors are regulated by other macromolecular complexes in the cilium. The ease of genetic and biochemical approaches combined with electron microscopy has provided the ability to perform in‐depth studies of the regulation of ciliary assembly and function. Results from Chlamydomonas researchers have broadened our knowledge of motile cilia diseases in humans. There are still many outstanding questions to be addressed. Key Concepts Chlamydomonas reinhardtii is a haploid, motile, single‐celled alga that is useful for the study of cilia. The Chlamydomonas cilium is a complex structure that generates asymmetric and symmetric waveforms to allow forward and backward swimming, respectively, and orientation to environmental signals. During ciliary motility, dynein arms pull microtubule doublets past each other to generate sliding, which is converted into axonemal bending, although the mechanism for how this occurs is still controversial. Outer dynein arms control the ciliary beat frequency by changing the velocity of doublet sliding. Inner dynein arms in conjunction with the radial spokes and the central pair apparatus, control the bend amplitude and the shape of the waveform. The axoneme is divided into 96 nm repeating segments that contain regulatory, enzymatic and structural components essential for motility; these include the inner and outer dynein arms, N‐DRC, MIA complex and radial spokes as well as two central microtubules. IFT (intraflagellar transport) is essential for building the cilium by transporting cargo into (anterograde) and out of (retrograde) the cilium. Cell biological research about ciliary components, including the central pair apparatus, radial spokes and N‐DRC, provides key information about how ciliary motility is regulated. Genetic, biochemical and microscopic methods used in Chlamydomonas have allowed molecular resolution of interactions between regulatory complexes. Studies of Chlamydomonas cilia have provided additional insights to the structure, function and regulation of cilia, and have helped with the understanding of human cilia‐related diseases called ciliopathies.

Biohybrid microrobots locally and actively deliver drug-loaded nanoparticles to inhibit the progression of lung metastasis

“…The corresponding motility ratio of microrobots decreased from 92.5 to 52.8% after 2 hours, which was also comparable to the change for the bare algae group. The alterations in speed and reduced motility are attributed to the effect of the higher temperature on the synthesis and function of the dynein protein, which, in turn, affects the beating of flagella ( 53 ). To further evaluate the impact of the NP(DOX) conjugation on the algae motility, the mean speed distribution of the algae-NP(DOX)-robots after 2 hours of operation at 37°C was also analyzed ( Fig.…”