Description
Periodic organ arrangements occur during growth and development and are widespread in both animals and plants. In bilaterian animals, repetitive organs are typically arranged periodically in a two-dimensional space defined by two body axes. In contrast, radially symmetrical animals and plants exhibit organ arrangements in three-dimensional space—around the body axis in animals and around the stem in plants. While the principles of periodic organ arrangement have been extensively studied in bilaterians, investigations in radially symmetrical animals remain limited.
In the present study, the authors combined live imaging, quantitative analysis, and mathematical modeling to elucidate periodic organ arrangement in a radially symmetrical animal, Coryne uchidai (Cnidaria, Hydrozoa). The polyps of C. uchidai simultaneously formed multiple tentacles in a regularly spaced, ring-like pattern exhibiting radial symmetry. Multiple such rings appeared periodically along the body and largely maintained symmetrical organization.
Additionally, the researchers observed polymorphisms in symmetry types—specifically tri-, tetra-, and pentaradial symmetries—occurring as individual variations. Notably, the type of radial symmetry was positively correlated with polyp diameter, with pentaradial polyps exhibiting a larger diameter than tetra- or triradial ones. Their mathematical model suggested that the selection of size-dependent radial symmetry is governed by activation-inhibition dynamics and positional information emanating from the mouth that guides tentacle initiation.
Funding Information
This work
was supported by Grants-in-Aid for Scientific Research from the
Ministry of Education, Culture, Sports, Science, and Technology of
Japan for SS (22KJ3132) and KF (21K19297 and 22H04719).