A half billion years ago. This helps us understand why most of the information in a life form cannot be in its genes.
Scientists have analyzed the genomes of two acorn worm species and found that approximately two-thirds of human genes have counterparts in the ancestors of these marine animals. These ancient genes, and their organization within the genome, were already in place in the common ancestor of humans and acorn worms that lived over half a billion years ago.
Around 550 million years ago, a great variety of animals burst onto the world in an event known as the Cambrian explosion. This evolutionary radiation revealed several new animal body plans, and changed life on Earth forever, as complex animals with specialized guts and behavioural features emerged. Thanks to the genome sequencing of multiple contemporary animals of the deuterostome group, we can go back in time to unveil aspects of the long-lost ancestor of this diverse group of animals.
Acorn worms are marine creatures that live on the ocean floor and feed by filtering a steady flow of sea water through slits in the region of their gut between mouth and esophagus. These slits are distantly related to the gills of fish, and represent a critical innovation in evolution not shared with animals like flies or earthworms. Since acorn worms occupy such a critical evolutionary position relative to humans the researchers sequenced two distantly related acorn worm species, Ptychodera flava, collected in Hawaii, and Saccoglossus kowalevskii, from the Atlantic Ocean. “Their genomes are necessary to fill the gap in our understanding of the genes shared by the common ancestor of all deuterostomes,” explains Dr Oleg Simakov, lead author of this study. More.
Here’s the abstract:
Acorn worms, also known as enteropneust (literally, ‘gut-breathing’) hemichordates, are marine invertebrates that share features with echinoderms and chordates. Together, these three phyla comprise the deuterostomes. Here we report the draft genome sequences of two acorn worms, Saccoglossus kowalevskii and Ptychodera flava. By comparing them with diverse bilaterian genomes, we identify shared traits that were probably inherited from the last common deuterostome ancestor, and then explore evolutionary trajectories leading from this ancestor to hemichordates, echinoderms and chordates. The hemichordate genomes exhibit extensive conserved synteny with amphioxus and other bilaterians, and deeply conserved non-coding sequences that are candidates for conserved gene-regulatory elements. Notably, hemichordates possess a deuterostome-specific genomic cluster of four ordered transcription factor genes, the expression of which is associated with the development of pharyngeal ‘gill’ slits, the foremost morphological innovation of early deuterostomes, and is probably central to their filter-feeding lifestyle. Comparative analysis reveals numerous deuterostome-specific gene novelties, including genes found in deuterostomes and marine microbes, but not other animals. The putative functions of these genes can be linked to physiological, metabolic and developmental specializations of the filter-feeding ancestor. Open access – Oleg Simakov et al., Hemichordate genomes and deuterostome origins. Nature, 2015; DOI: 10.1038/nature16150
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