“The ctenophore genome and the evolutionary origins of neural systems”
Leonid L. Moroz1,2,3, Kevin M. Kocot4, Mathew R. Citarella1, Sohn Dosung1, Tigran P. Norekian1,3, Inna S. Povolotskaya5,6,
Anastasia P. Grigorenko7,8, Christopher Dailey9, Eugene Berezikov10, Katherine M. Buckley11, Andrey Ptitsyn1, Denis Reshetov8,
Krishanu Mukherjee1, Tatiana P. Moroz1, Yelena Bobkova1, Fahong Yu2, Vladimir V. Kapitonov12, Jerzy Jurka12, Yuri V. Bobkov1,
Joshua J. Swore1,3, David O. Girardo1,3, Alexander Fodor1, Fedor Gusev7,8, Rachel Sanford1, Rebecca Bruders1,3, Ellen Kittler13,
Claudia E. Mills3, Jonathan P. Rast11, Romain Derelle5,6, Victor V. Solovyev14, Fyodor A. Kondrashov5,6,15, Billie J. Swalla3,
Jonathan V. Sweedler9, Evgeny I. Rogaev7,8,16,17, Kenneth M. Halanych4 & Andrea B. Kohn1
The origins of neural systems remain unresolved. In contrast to other basal metazoans, ctenophores (comb jellies) have bothcomplex nervous and mesoderm-derived muscular systems. These holoplanktonic predators also have sophisticated ciliated locomotion, behaviour and distinct development. Here we present the draft genome of Pleurobrachia bachei, Pacific sea gooseberry, together with ten other ctenophore transcriptomes, and show that they are remarkably distinct from other animal genomes in their content of neurogenic, immune and developmental genes. Our integrative analyses place Ctenophora as the earliest lineage within Metazoa. This hypothesis is supported by comparative analysis of multiple gene families, including the apparent absence ofHOXgenes, canonical microRNAmachinery, and reducedimmunecomplement in ctenophores. Although two distinct nervous systems are well recognized in ctenophores, many bilaterian neuron-specific genesandgenes of ‘classical’ neurotransmitter pathways eitherare absent or, if present, arenot expressed in neurons. Our metabolomic and physiological data are consistent with the hypothesis that ctenophore neural systems, and possibly muscle specification, evolved independently from those in other animals.
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