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 exhibit diverse structures and functions across different eukaryotic organisms, elaborated by gene specialization and the incorporation of accessory proteins, enabling 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 extraordinary 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 remain unclear.

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 components of cytoskeleton to achieve their remarkable dynamic shape-shifting ability. This study was published in Current Biology.

In this study, the researchers elucidated the molecular composition of the neck based on a high-quality genome of Lacrymaria through mass spectrometry analysis. Their results indicated 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 composed of centrin-myosin proteins and a microtubule cytoskeleton that contains a novel giant protein. Also, Plasmodium-like unconventional actin was discovered, 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.

These findings are highly significant for understanding the cell movement, as well as the evolution and diversity of cytoskeleton. Furthermore, they provide valuable insights for future biomimetic designs in microscale robotics.

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

Hypothetical molecular model depicting neck deformation in Lacrymaria (Image by IHB)

(Editor: MA Yun)