February 19, 2021
Keio University
Maki Wakai, a second-year master's student in the School of Fundamental Science and Technology, Graduate School of Science and Technology at Keio University, along with Professor Kotaro Oka and Associate Professor Koji Hotta, have revealed that sea squirts become adults by transmitting environmental changes to calcium ions within their bodies. Calcium ions are involved in various signal transductions in life phenomena as second messengers. In this study, they visualized the spatiotemporal changes in intracellular calcium ion concentration during the process of sea squirt metamorphosis into an adult and investigated the intracellular molecular mechanisms that induce this transformation.
Many marine organisms undergo metamorphosis from planktonic larvae to sessile adults that attach to surfaces like rocks. It is known that metamorphosis is triggered by various environmental signals such as light, chemical substances, and mechanical stimuli, but it was not understood how these stimuli are transmitted within the body to induce metamorphosis.
In sea squirts as well, the tadpole-like larvae attach via a sensory organ called the "papilla" located at their anterior end, and this attachment triggers metamorphosis. The papillae are thought to transmit environmental stimuli into the body as a cue for metamorphosis, but it has been difficult to capture the phenomena occurring inside the motile larvae, and how the metamorphosis signal is transmitted was unknown. This research group succeeded in freely inducing metamorphosis by controlling the timing and location of larval attachment, and for the first time in the world, they successfully observed the calcium dynamics in sea squirt larvae during metamorphosis. As a result, they found that mechanical stimulation to the papillae for a certain duration acts as a switch for metamorphosis, transmitting the signal to start metamorphosis to various internal organs as a change in calcium ion concentration.
Many aspects of the series of mechanisms from attachment to metamorphosis remain unclear. The findings of this research are expected to contribute significantly to the understanding of metamorphosis mechanisms in marine organisms and to help solve problems related to aquaculture, fishery damage, and the maintenance of biodiversity. The research findings were published online in the British scientific journal "Proceedings of the Royal Society B" on February 17, 2021 (UK time).
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