engleski

Comparative genomics reveals broad genetic repertoire of simplest metazoans – sponges (Porifera)

Some of the fundamental questions in animal evolution are the time of origin of genome complexity and the relation between morphological and genomic complexity. Traditional view was that simple animals have simple genomes and that genome complexity progressively increases in “ higher” or more complex animals. With more data becoming available from “ lower” animals this view is changing and basal metazoans are becoming increasingly interesting research subject. Complete genome sequence of sea anemone Nematostella vectensis clearly shows that much of the genomic complexity was already present in the ancestor of all Eumetazoa. Sponges (Porifera) are the simplest extant and probably the earliest branching metazoan phylum. However, previous research showed that they possess a number of genes/proteins found also in deuterostomes but not in protostomes, ancient duplications and diversifications of several gene families have been documented in sponges and it has been determined that sponge proteins are often more similar to their Homo sapiens orthologues than to Caenorhabditis elegans and/or Drosophila melanogaster orthologues. Potential problems with these studies were a possible bias in choosing genes/proteins for analysis and the relatively low number of sequenced sponge genes. In order to evaluate sponge genetic complexity and consequently the genetic complexity of the common ancestor of all Metazoa (Urmetazoa) without partiality and to further elucidate metazoan genome evolution, we employed random EST sequencing approach. Two demosponge species were used for the analyses – Suberites domuncula with 4646 unique transcript sequences and Lubomirskia baicalensis with 1335 unique transcript sequences. We identified and compared sponge protein homologues from six model organisms with complete genome sequences: Nematostella vectensis, Caenorhabditis elegans, Drosophila melanogaster, Strongylocentrotus purpuratus, Ciona intestinalis and Homo sapiens. Our results strongly indicate that, measured by gene content, sponges have complex genomes. This finding implies that the ancestor of all metazoans (Urmetazoa) also had a complex genome.

sponges; Porifera; genome; Suberites domuncula

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