Heliozoan Raphidocystis contractilis withdraws its axopodia a few milliseconds after coming across an external stimulus. Researchers from Okayama University, Japan report that microtubule characteristics hold the key to this instant arm reducing. Credit: Motonori Ando from Okayama University
Researchers have actually discovered the genes and proteins accountable for the fast withdrawal of heliozoan arms in response to changes in the environment. This is one of the fastest-known examples of cell motility.
Raphidocystis contractilis is a type of eukaryote in the Heliozoa group, discovered in fresh, brackish, and sea water. These organisms are called “solar worms” due to their radiating finger-like arms, or axopodia, which offer them a sun-like look.
The axopodia of R. contractilis are made of alpha-beta tubulin heterodimers, which form microtubules. Regardless of its ability to rapidly withdraw its arms in response to stimuli, the mechanism behind this fast arm reducing is a mystery.
To this end, a group of scientists including Professor Motonori Ando, Dr. Risa Ikeda (both from the Laboratory of Cell Physiology), and Associate Professor Mayuko Hamada (from the Ushimado Marine Institute), of Okayama University, Japan, checked out the mechanism involved in one of the fastest cell movements in the living world.
So, where did it all start? Sharing the inspiration behind their study, Professor Ando states, “Recently, a wide range of heliozoans have actually been found in different hydrospheres in the Okayama Prefecture, making it clear that several types of sun worms occupy the exact same environment. We are trying to decipher the mysteries around these protozoans and slowly expand the horizons of our knowledge.”
The authors began their examination by immunolabelling the tubulin protein and observing its movement prior to and after axopodial contraction. They found that prior to reducing, tubulins were set up methodically all along the length of the axopodia, but after axopodial withdrawal, those quickly built up at the cell surface. This led them to believe that throughout the rapid axopodial withdrawal, the microtubules broke down into tubulin quickly. Microtubule deterioration is normally not a quick phenomenon; it advances rather slowly.
How then, could R. contractilis attain this modification so quickly?
If the microtubules divided at numerous sites at the same time, the researchers hypothesized that this was possible. To validate their hypothesis, the authors set out to find the proteins and genes included in the instant cleavage of microtubules in R. contractilis. Their findings were recently published in The Journal of Eukaryotic Microbiology.
The researchers performed de novo transcriptome sequencing (analysis of the genes revealed at a specific time in a cell) and recognized near 32,000 genes in R. contractilis. This gene set was most comparable to that found in protozoans (which are single-celled organisms), followed by metazoans (multicellular organisms with well-differentiated cells; this includes people, and other animals).
Homology and phylogenetic analysis of the acquired gene set exposed numerous genes (and their corresponding proteins) involved in microtubule disruption. Several duplicates of kinesin genes were found. Calcium signaling genes control the entry of calcium ions into the cell from its environments and the induction of axopodial withdrawal.
The scientists also noticed a lack of genes connected with flagellar development and motility, indicating that the axopodia of R. contractilis have actually not evolved from flagella. Many genes stay unclassified, the newly established gene set will serve as a reference for future studies intending to comprehend the axopodial motility of R. contractilis.
Heliozoan axopodia can function as a sensitive sensing unit. They can discover minute modifications in their environment, e.g., the presence of heavy metal ions and anticancer drugs. Discussing their vision for the future, Professor Ando shares, “We think that the axopodial reaction of heliozoa can be utilized as an index to develop short-term detection and monitoring gadgets for environmental and faucet water contamination. It can likewise be used as an unique bioassay system for the primary screening of novel anticancer drugs. In the future, we plan to continue to collaborate as a group to improve applied and basic research study on these organisms.”
Heliozoans have shown yet once again that a single cell has tremendous potential to change the world. We wish the authors success in turning their vision to reality!
Recommendation: “De novo transcriptome analysis of the centrohelid Raphidocystis contractilis to recognize genes involved in microtubule-based motility” by Risa Ikeda, Tosuke Sakagami, Mayuko Hamada, Tatsuya Sakamoto, Toshimitsu Hatabu, Noboru Saito and Motonori Ando, 21 November 2022, Journal of Eukaryotic Microbiology.DOI: 10.1111/ jeu.12955.
The research study was funded by the Japan Society for the Promotion of Science and the Research Institute of Marine Invertebrates..
Scientists from Okayama University, Japan report that microtubule dynamics hold the secret to this instant arm shortening. To confirm their hypothesis, the authors set out to find the proteins and genes involved in the instant cleavage of microtubules in R. contractilis. Homology and phylogenetic analysis of the gotten gene set revealed several genes (and their matching proteins) included in microtubule interruption. A number of duplicates of kinesin genes were discovered. Calcium signaling genes regulate the entry of calcium ions into the cell from its environments and the induction of axopodial withdrawal.
