Recently, a research group led by Prof. MIAO Wei from the Institute of Hydrobiology (IHB) of the Chinese Academy of Sciences discovered that Lacrymaria cells utilize unconventional and novel cytoskeletal components to achieve their remarkable dynamic shape-shifting ability. This study was published in Current Biology.

Eukaryotic cells rely on dynamic shape changes to fulfill various cellular functions, sustain vital biological processes, and regulate cellular behavior. These shape changes are largely driven by the organization and arrangement of cytoskeletal components. Cytoskeletons, produced by gene specialization and the incorporation of accessory proteins, enable cells to have different shapes and roles.

Many eukaryotic cells exhibit shape changes, with one of the most fascinating examples being the unicellular ciliated eukaryote Lacrymaria, known for its extraordinarily dynamic shape-shifting. It possesses a flexible “cell neck” that can extend several to tens of times its body length to capture prey, showing astonishing elasticity and freedom of motion. Despite much research, the molecular mechanisms underlying this extreme morphological change have not been understood.

In this study, through mass spectrometry analysis, the researchers elucidated the molecular composition of the neck based on a high-quality genome of Lacrymaria. They found that the remarkable morphological change in Lacrymaria involves a unique actin-myosin system rather than the Ca²⁺-dependent system found in other contractile ciliates.

Based on various experimental evidence, the researchers revealed that the molecular and structural basis of the neck contraction system in Lacrymaria consists of a myoneme cytoskeleton, which is composed of centrin-myosin proteins, and a microtubule cytoskeleton that contains a novel giant protein.

In addition, they discovered Plasmodium-like unconventional actin, which may form highly dynamic short filaments that facilitate coordination between these two cytoskeletons, thereby driving the extreme cellular deformation of Lacrymaria cells.

“Actually, this is the second novel cytoskeletal system discovered in ciliates, following our earlier findings in Spirostomum. Eukaryotes exhibit a diverse range of cytoskeletal systems, and ciliates like Lacrymaria and Spirostomum, known for their extraordinary cellular motility, provide excellent models for investigating these novel cytoskeletal systems,” said Prof. MIAO.

The findings of this study are highly significant for understanding cell movement, as well as evolution and diversity, in cytoskeletons. Also, they provide valuable insights for future biomimetic microscale robotic designs.

Two cytoskeletal structures of the single-celled eukaryote, Lacrymaria (Image by IHB)