engleski

How complex is sponge genome?

During the last 15 years a large amount of data about the structure and function of genes/proteins from different sponges (Porifera) has been accumulated. The majority of molecular genetic data were collected from the marine demosponge Suberites domuncula. Based on these data, supported in many cases by cell biological studies, it is now well established that all metazoan phyla evolved from one ancestor, the hypothetical Urmetazoa. Although sponges are the simplest living multicellular animals, their genomes are far from being simple. Bases on the information obtained from thousands of partial cDNA sequences (ESTs), hundreds of complete cDNA sequences and dozens of gene sequences from S. domuncula, we can only conclude that the genome of (at least) this demosponge is unexpectedly complex. It encodes thousand of proteins, including many sophisticated proteins involved in higher order processes and biological functions found so far exclusively in higher animals. These proteins include, for example, numerous receptor and cytoplasmic tyrosine kinases and Ras family small GTPases, molecules involved in cell-cell interactions, morphogenesis, immune response, apoptosis, skeleton formation etc. In addition, many genes/proteins from S. domuncula with clear orthologs in human are not encoded in Caenorhabditis elegans or Drosophila melanogaster genomes. Another unexpected finding came from the detailed analysis of sponge genes/proteins. The majority of S. domuncula genes and proteins are more related to their orthologs in vertebrates/mammals/human that to either D. melanogaster or C. elegans counterparts: 1) intron positions in sponge and mammalian orthologous genes are highly conserved, what is often not true for orthologs from insects and worms ; 2) sponge proteins show on average highest degree of sequence similarity with proteins from vertebrates (including mammals). In addition, when orthologs (or even whole protein families like ribosomal proteins) from S. domuncula, D. melanogaster, C. elegans and mammals are compared, the highest degree of sequence conservation is often found between sponge and mammalian protein pairs. Both model invertebrate organisms experienced recently accelerated evolution. Significant number of D. melanogaster and C. elegans genes are highly modified and nothing is known about the extent of gene loss in these model organisms. Therefore, sponge genes/proteins very probably better reflect the structure and complexity of the ancestral metazoan genome (Urmetazoa), which obviously already encoded huge number of proteins, including many metazoan “ novelties” . These ancient genes/proteins, common to all Metazoa, changed to the less extent during the evolution of Deuterostomia (and sponges) than during the evolution of two model invertebrates. The complete information about gene content and complexity of sponge genome (“ Sponge sequencing project” ) will be of extreme importance for the elucidation of metazoan evolution.

evolution; Metazoa

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