Last Ancestor Humans Shared With Worms Had Sophisticated Brain, microRNAs Show
ScienceDaily (Feb. 2, 2010) — The last ancestor we shared with worms, which roamed the seas around 600 million years ago, may already have had a sophisticated brain that released hormones into the blood and was connected to various sensory organs. The evidence comes not from a newly found fossil but from the study of microRNAs -- small RNA molecules that regulate gene expression -- in animals alive today.
The marine ragworm Platynereis dumerilii. (Credit: Udo Ringeisen/EMBL)
Animals from different branches of the evolutionary tree -- different lineages -- possess specific microRNAs that evolved only in their lineage. But they also have microRNAs in common: ones which they inherited from their last common ancestor, and which have been conserved throughout animal evolution.
The EMBL scientists looked at the marine annelid Platynereis dumerilii, which is thought to have changed little over the past 600 million years. They visualised where these conserved microRNAs are expressed, and compared Platynereis with other animals. They found that inPlatynereis these microRNAs are highly specific for certain tissues and cell types and, what is more, discovered that tissue specificity was conserved over hundreds of millions of years of evolutionary time.
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Letter
Nature advance online publication 31 January 2010 | doi:10.1038/nature08744; Received 31 July 2009; Accepted 4 December 2009; Published online 31 January 2010
Ancient animal microRNAs and the evolution of tissue identity
Foteini Christodoulou1, Florian Raible1,2,4, Raju Tomer1, Oleg Simakov1, Kalliopi Trachana2, Sebastian Klaus1,4, Heidi Snyman1, Gregory J. Hannon3, Peer Bork2 & Detlev Arendt1
1. Developmental Biology Unit,
Foteini Christodoulou1, Florian Raible1,2,4, Raju Tomer1, Oleg Simakov1, Kalliopi Trachana2, Sebastian Klaus1,4, Heidi Snyman1, Gregory J. Hannon3, Peer Bork2 & Detlev Arendt1
1. Developmental Biology Unit,
2. Computational Biology Unit, European Molecular Biology Laboratory, D-69117 Heidelberg, Germany
3. Cold Spring Harbor Laboratory, 1 Bungtown Road, Cold Spring Harbor, New York 11724, USA
Present addresses: Max F. Perutz Laboratories, Campus Vienna Biocenter, Dr. Bohr-Gasse 9/4, A-1030 Vienna, Austria (F.R.); J. W. Goethe - Universität Frankfurt Biologie-Campus, Siesmayerstrasse 70-72, D-60323 Frankfurt, Germany (S.K.).
Correspondence to: Detlev Arendt1 Correspondence and requests for materials should be addressed to D.A. (Email: arendt@embl.de).
Correspondence to: Detlev Arendt1 Correspondence and requests for materials should be addressed to D.A. (Email: arendt@embl.de).
The spectacular escalation in complexity in early bilaterian evolution correlates with a strong increase in the number of microRNAs1, 2. To explore the link between the birth of ancient microRNAs and body plan evolution, we set out to determine the ancient sites of activity of conserved bilaterian microRNA families in a comparative approach. We reason that any specific localization shared between protostomes and deuterostomes (the two major superphyla of bilaterian animals) should probably reflect an ancient specificity of that microRNA in their last common ancestor. Here, we investigate the expression of conserved bilaterian microRNAs in Platynereis dumerilii, a protostome retaining ancestral bilaterian features3, 4, in Capitella, another marine annelid, in the sea urchin Strongylocentrotus, a deuterostome, and in sea anemone Nematostella, representing an outgroup to the bilaterians. Our comparative data indicate that the oldest known animal microRNA, miR-100, and the related miR-125 and let-7 were initially active in neurosecretory cells located around the mouth. Other sets of ancient microRNAs were first present in locomotor ciliated cells, specific brain centres, or, more broadly, one of four major organ systems: central nervous system, sensory tissue, musculature and gut. These findings reveal that microRNA evolution and the establishment of tissue identities were closely coupled in bilaterian evolution. Also, they outline a minimum set of cell types and tissues that existed in the protostome–deuterostome ancestor.
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