We tend to think of cells as little balls or elongated structures surrounded by a membrane, containing a single nucleus and maybe some other organelles, such as mitochondria floating within a cytoplasm. However, even within human anatomy, long, elongated and multinucleated cells can be found, notably in our skeletal muscles, but also in lung tissue following infection with the Respiratory Syncytial Virus (RSV).
These multinucleate cells are commonly referred to as syncytia and are formed by the fusion of cells. Syncytia can reach sizes up to centimeters, compared to 10-100 micrometers for an average eukaryotic cell. Moreover, syncytia may contain up to thousands of nuclei. Big choirs need a conductor to keep the singers in tune, so how do syncytia keep their nuclei in sync, or rather, how do they coordinate gene regulation between their numerous and widely dispersed nuclei?
To study how syncytia achieve coordinated nuclear states, Prof. Karen Alim, professor of Biological Physics and Morphogenesis, and her research group use a slime mold called Physarum polycephalum, commonly referred to as “the blob”. This organism can be cultivated in the lab as microplasmodia, a small multinucleate state and, when put in small droplets on a plate with gel substrate, be induced to fuse into multinucleate networks (i.e., syncytia).
These syncytia form a tubular network enabling cytoplasmic shuttle flows to transport intra-cellular signals. This network rhythmically contracts, thus inducing a back-and-forth flow within the tubes. Microscopic tracking of individual nuclei within the syncytia revealed the presence of very mobile nuclei, moving faster the closer they get to the center of the tube, as well as nuclei that are trapped within the porous gel cortex lining the inside of the tube wall. Importantly, mobile nuclei can become trapped, whereas trapped nuclei can become mobile again. Moreover, mobile nuclei do not continue to travel along the tubes, instead they return to their original positions. These results show the presence of a new messaging relay system within syncytia, reminiscent of pigeon post.
A mobile nucleus transports a signal to a further immobile nucleus, passes the signal, and then returns “home" (carrier pigeon 1). The signal will then be picked up by a second mobile nucleus (carrier pigeon 2) that will transport it back to its own home further along the tube, and so on. Thus, the pigeons (mobile nuclei) shuttle back and forth between two positions within the tube, increasing the speed of information dissemination by up to 20 times. Even better, this relay system is bi-directional along the tubes.
This new system provides valuable new insight into how molds may undergo synchronous nuclear division and explain why cytoplasmic flows are crucial for this process.
Publication
Coexistence of trapped and flow-transported nuclei enables fast pigeon-post communication across multi-nucleated cell. Johnny Tong, Kaspar Wachinger, Fabian K. Henn, Nico Schramma, Siyu Chen and Karen Alim. PNAS https://doi.org/10.1073/pnas.2411101122
More information and links
- Julie Zaugg (17 October 2019). "The 'blob': Paris zoo unveils unusual organism which can heal itself and has 720 sexes".
- This work was supported by the TUM Innovation Network RISE and the Human Frontier Science Program.
Contact about the article
Prof. Karen Alim
Professorship of Biological Physics and Morphogenesis
TUM School of Natural Sciences
k.alim(at)tum.de
Press Contact
communications(at)nat.tum.de
Team website