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Nervous system evolution : insights from the sea urchin

Abstract : Nervous systems in metazoans range from simple nerve nets to complex centralized organs. Because of such diversity, the evolutionary history of nervous system in metazoans has been heavily debated. Echinoderms are a large group of metazoans that constitute with the hemichordates the clade of the ambulacrarians, within the deuterostomes. So far, adult echinoderms have been largely ignored in comparative biology because they exhibit a large set of anatomical oddities. However, a careful examination of neural patterning and organization in adult echinoderms is needed to decipher nervous system evolution in deuterostomes. To achieve this goal, we first improved the husbandry protocol for the sea urchin species Paracentrotus lividus to obtain suitable quantities of post-metamorphic individuals for experimentations. Then, we facilitated the study of post-metamorphic echinoids by staging the development of P. lividus from fertilization to post-metamorphic juvenile stages. Finally, we yielded an exhaustive body-wide description of the neuromuscular anatomy of post-metamorphic P. lividus juveniles which indicated that the nervous system of adult echinoids is not strictly centralized as it also includes elements that are typical of nerve nets. Similar investigation in post-metamorphic specimens of the sea star Patiria miniata and the sea cucumber Parastichopus parvimensis revealed a similar organization. Finally, we started a molecular screening of neural patterning genes in post-metamorphic P. lividus and P. miniata juveniles, suggesting that a genetic program similar to the one found in hemichordates is also used to pattern the ectoderm of adult echinoderms.
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Laurent Formery. Nervous system evolution : insights from the sea urchin. Invertebrate Zoology. Sorbonne Université, 2019. English. ⟨NNT : 2019SORUS620⟩. ⟨tel-03374193⟩

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