Early Stages of Animal Mesoderm Evolution.

Sequencing of genomes of unicellular eukaryotes Holozoa (Monosiga brevicollis, Capsaspora owczarzaki), basal multicellular Porifera and Cnidaria, and Bilateria showed that the gene repertoire and gene regulatory networks that play a key role in the evolution of multicellular animals, in particular, in the formation of the mesoderm, have an earlier origin than was expected. The appearance of Cnidaria and Bilateria occurred before the Cambrian explosion when an unprecedented number of new forms of organisms evolved. It is assumed that the molecular genetic basis of the Cambrian explosion was preceded by Hox genes, which provided a fundamental complication of the genetic developmental programs of Bilateria (Erwin and Davidson, 2002; Davidson, 2006; Carroll, 2008; Holland, 2015). [ABSTRACT FROM AUTHOR]