最近的研究工作表明，微RNA（普遍存在的小型非编码遗传元素，具有重要调控作用）在多细胞动物复杂性的演化中起重要作用。那么当这些微RNA最初形成时其作用是什么呢？

对海生沙蚕（岩虫）（Platynereis dumerilii）所做的一项深度测序研究及与其他两侧对称动物所做比较表明，已知最古老的微RNA（即miR-100）最初在口腔周围的神经分泌细胞中是活跃的。其他高度保守的微RNA最初存在于特定组织和器官系统中，如纤毛细胞、神经系统的部分地方、肌肉组织和肠道。这项工作表明，两侧对称动物的最后共同祖先已经具有所有这些结构了。

原始出处：

Nature 463, 1084-1088 (25 February 2010) | doi:10.1038/nature08744

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,
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
4 Present addresses: Max F. Perutz Laboratories, Campus Vienna Biocenter, Dr. Bohr-Gasse 9/4, A-1030 Vienna, Austria (F.R.); J. W. Goethe - Universit?t 5 Frankfurt Biologie-Campus, Siesmayerstrasse 70-72, D-60323 Frankfurt, Germany (S.K.).
6 Correspondence to: Detlev Arendt1 Correspondence and requests for materials should be addressed to D.A.

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.