Researchers have made an astonishing discovery by studying an atypical single-celled organism, Euplotes patella. Their study reveals in particular that it uses its 14 small legs in surprisingly varied ways, as if a mechanical computer were controlling them. For this, the animal uses among other things its microtubules (constituent fibers of the cytoskeleton). A discovery that could help explain how many other single-celled organisms adopt complex behaviors despite the absence of a brain or nervous system.
Before becoming interested in this microorganism, Ben Larson of the University of California at San Francisco (UCSF) noticed that the cells he was trying to study in other research work were constantly devoured by predators capable of moving on surfaces with an atypical gait, similar to that of insects. It was there that he thought of Wallace Marshall, an expert in unusual microorganisms, whom he ended up contacting in an attempt to find out more about these animals that were interfering with his research.
Soon after, the two researchers identified the predators as single-celled organisms belonging to the genus Euplotes, Euplotes patella. These predatory protists are found in the sea as well as in fresh water. They can swim but also walk on surfaces underwater using around 14 cirri (or legs) on their underside (the number varies depending on the species), controlled by microtubules.
” If we can make a computer from microtubules, we can justify looking for them in many other types of cells Says Marshall, a member of the new study team at UCSF.
Euplotes: a surprisingly irregular gait
Since the turn of the 20th century, biologists have wondered how unicellular creatures devoid of nerves can coordinate the movements of so many legs. So Larson, Wallace and their colleagues decided to study Euplotes in more detail.
Larson started by taking videos of 13 Euplotes cells walking on a glass microscope slide. He then painstakingly annotated each cirre (leg) in each video frame so the team could analyze the gait in detail. This revealed that the Euplotes have a very unusual gait …
To better understand the following, you should know that animals with brains, like centipedes, usually repeat the same pattern of paw movements over and over again. Instead, Euplotes’ paws move in many different patterns.
” There is no exact, well-defined sequence of steps they take, there is a lot of variability Larson explains. This could be explained by the fact that the animal is not able to perform regular and repetitive movements of the legs, but it could also be an adaptation to walking on rough surfaces that it does not ‘is not able to detect. Designers of walking robots usually add some variability to keep their machines from getting stuck, Wallace points out. It could therefore be a similar “preventive” mechanism brought about by evolution.
However, the movement of Euplotes’ legs is not entirely random either. This indicates that an internal system controls and coordinates the movements of the paws to some extent. ” There is some kind of information that is transmitted Larson says.
The first candidate is the bundle of microtubules which extend inside the cell from where each leg connects to the cell, and which are connected to each other. The team therefore added a drug known to disrupt the formation of microtubules to the water. As expected, this altered the gait of the cells, causing the legs to move in different patterns. The Euplotes were going around in circles…
Microtubules: they act like a kind of mechanical computer
The results suggest that the microtubule network acts like a kind of simple mechanical computer, called a “finite automaton”, or “finite state machine”. ” Our data shows that it takes microtubules for calculus to occur. The simplest explanation is that these are the elements of calculation Marshall says. ” Have we proven it? No “. Details have been posted to the preprint server bioRxiv.
” It is a very solid scientific work Says Robert Blick of the University of Hamburg in Germany, which designs nanomechanical computers. ” Aspects of mechanics are undervalued in biology and even in biophysics “. The team must now do more research to definitively show that microtubules act like a finite state machine, according to Blick. ” If so, it could be a game-changer “.
Many single-celled organisms are capable of very sophisticated behaviors. But how creatures devoid of nerves or brains achieve this remains a mystery. ” All these behaviors are still mysterious Says Wallace. Microtubules are present in all complex cells, so they could control the behavior of other cells as well.