Wakai Maiki K, Nakamura Mitsuru J, Sawai Satoshi, Hotta Kohji, Oka Kotaro
Department of Biosciences and Informatics, Faculty of Science and Technology, Keio University, Kouhoku-ku, Yokohama 223-8522, Japan.
Graduate School of Arts and Sciences, University of Tokyo, Komaba, 153-8902 Tokyo, Japan.
Proc Biol Sci. 2021 Feb 24;288(1945):20203207. doi: 10.1098/rspb.2020.3207. Epub 2021 Feb 17.
Marine invertebrate larvae are known to begin metamorphosis in response to environmentally derived cues. However, little is known about the relationships between the perception of such cues and internal signalling for metamorphosis. To elucidate the mechanism underlying the initiation of metamorphosis in the ascidian, type A (), we artificially induced ascidian metamorphosis and investigated Ca dynamics from pre- to post-metamorphosis. Ca transients were observed and consisted of two temporally distinct phases with different durations before tail regression which is the early event of metamorphosis. In the first phase, Phase I, the Ca transient in the papillae (adhesive organ of the anterior trunk) was coupled with the Ca transient in dorsally localized cells and endoderm cells just after mechanical stimulation. The Ca transients in Phase I were also observed when applying only short stimulation. In the second phase, Phase II, the Ca transient in papillae was observed again and lasted for approximately 5-11 min just after the Ca transient in Phase I continued for a few minutes. The impaired papillae by -knockdown failed to induce the second Ca transient in Phase II and tail regression. In Phase II, a wave-like Ca propagation was also observed across the entire epidermis. Our results indicate that the papillae sense a mechanical cue and two-round Ca transients in papillae transmits the internal metamorphic signals to different tissues, which subsequently induces tail regression. Our study will help elucidate the internal mechanism of metamorphosis in marine invertebrate larvae in response to environmental cues.
已知海洋无脊椎动物幼虫会响应环境衍生线索而开始变态。然而，对于此类线索的感知与变态的内部信号传导之间的关系却知之甚少。为了阐明海鞘A 型（ ）变态起始的潜在机制，我们人工诱导海鞘变态，并研究了从变态前到变态后的钙动态变化。观察到钙瞬变，其在变态早期事件——尾部退化之前由两个时间上不同且持续时间不同的阶段组成。在第一阶段，即阶段I，在机械刺激后不久，乳头（前躯干部的粘附器官）中的钙瞬变与背侧定位细胞和内胚层细胞中的钙瞬变相关联。仅施加短刺激时也观察到了阶段I中的钙瞬变。在第二阶段，即阶段II，在阶段I中的钙瞬变持续几分钟后，乳头中的钙瞬变再次出现并持续约5 - 11分钟。通过敲低 而受损的乳头未能诱导阶段II中的第二次钙瞬变和尾部退化。在阶段II中，还观察到一波状钙在整个表皮中传播。我们的结果表明，乳头感知机械线索，乳头中的两轮钙瞬变将内部变态信号传递到不同组织，随后诱导尾部退化。我们的研究将有助于阐明海洋无脊椎动物幼虫响应环境线索的变态内部机制。
