The newly discovered sensors are termed filopodia. These structures can extend outwards, contract and bend through a series of dynamic movements. Scientists think that cell interaction with their environment is critical to their function.
The filopodia are described as tube-like protrusions, or slender cytoplasmic projections, which spring out from the cell membrane (cytoplasm is the fluid that fills a cell.) These finger-like extensions collect messages and take these signals back to the cell. The information tells the cell about the shape and structure of the environment and the levels of chemicals present. As an example disease hunting cells in the human body, such as macrophages would use such information in order to travel towards pathogenic bacteria and attack them. Here, the filopodia act as phagocytic tentacles and pull bound objects towards the cell for phagocytosis (where the macrophage ‘eats’ the invasive bacterium.)
The filopodia are not simply static structures. They have the ability to contract, bend and elongate in multiple directions. To find out more about these structures, a research group used a special type of microscope contained in a specially designed box. This box allowed the researchers to influence the cells using a laser.
To collect readings, the scientists placed a small plastic object on the end of the filopodia structure. This enabled them to collect ultrasensitive force measurements. They also used a special dye to visualise the movement and motion of the structures.
Through this the researchers learnt a considerable amount about the forces involved. For example, they discovered that actin inside the filopodia showed a marked twisting motion. When the material drew back, spiral folds were formed in a similar way to twisting a rubber band. It seems that spiral shapes are common in nature, even down to the structure of DNA.
The study was conducted at the University of Copenhagen – Niels Bohr Institute. The findings have been published in the journal, Proceedings of the National Academy of Sciences. The paper is headed “Helical buckling of actin inside filopodia generates traction.”
