Abstract
The Cambrian explosion was a unique animal radiation ~540 million years ago that produced the full range of body plans across bilaterians. The genetic mechanisms underlying these events are unknown, leaving a fundamental question in evolutionary biology unanswered. Using large-scale comparative genomics and advanced orthology evaluation techniques, we identified 157 bilaterian-specific genes. They include the entire Nodal pathway, a key regulator of mesoderm development and left-right axis specification; components for nervous system development, including a suite of G-protein-coupled receptors that control physiology and behaviour, the Robo-Slit midline repulsion system, and the neurotrophin signalling system; a high number of zinc finger transcription factors; and novel factors that previously escaped attention. Contradicting the current view, our study reveals that genes with bilaterian origin are robustly associated with key features in extant bilaterians, suggesting a causal relationship.
Highlights
The taxon Bilateria consists of multicellular animals with bilateral body symmetry and constitutes a major and ancient radiation of animals
1–Figure 1; Supplementary File 1–Supplementary Table 5), we focused our analysis on 75,744 orthogroups (OGs) with at least ten species
In line with previous ndings (Hudson and Yasuo, 2005; Shen, 2007; Grande et al, 2014; Kenny et al, 2014), our analysis revealed that the TGF- ligand Nodal belongs to a robust bilaterianspeci c orthogroup (OG_12210; Figure 5–Figure Supplement 2, Supplementary File 1–Supplementary Table 14)
Summary
The taxon Bilateria consists of multicellular animals with bilateral body symmetry and constitutes a major and ancient radiation of animals. There is compelling morphological and molecular evidence for the monophyly of bilaterians (Hejnol et al, 2009; Dunn et al, 2014; Cannon et al, 2016), for their subdivision into protostomes and deuterostomes (Aguinaldo et al, 1997; Philippe et al, 2005; Dunn et al, 2008; Simakov et al, 2013; Cannon et al, 2016), and for the overall relationships of. Ì25 phyla that make up this group (Dunn et al, 2008; Hejnol et al, 2009; Dunn et al, 2014). Mya), stem groups of all major bilaterian phyla inhabited Earth. This abrupt appearance of most bilaterian body plans, the sets of morphological features common to a phylum, already puzzled
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