Protein tyrosine kinases, which are involved in diverse cellular functions, are broadly classified as cytoplasmic tyrosine kinases and receptor tyrosine kinases. Because tyrosine kinases played important roles in the evolution of multicellular organisms, Suga et al. investigated the evolution of this group of kinases by performing a genomic screen of the tyrosine kinase-encoding genes of the only two known members of the Filasterea, a type of singlecelled eukaryote.

Through phylogenetic analysis and by comparing tyrosine kinase-encoding sequences from the Filasterea with those from other organisms, such as animals (metazoans) and choanoflagellates (unicellular organisms considered to the be the closest relatives to metazoans), the authors showed that cytoplasmic tyrosine kinases were established and diversified before the onset of multicellularity, whereas receptor tyrosine kinases evolved rapidly and separately in the various lineages after the establishment of metazoans.

The differences in the speed and mode of evolution between cytoplasmic tyrosine kinases and receptor tyrosine kinases raise interesting questions about the roles of these tyrosine kinases in unicellular organisms.

Reference Article: Suga, H., Dacre M., de Mendoza A.,  Shalchian-Tabrizi K., Manning, G., Ruiz-Trillo I. 2012. Genomic Survey of Premetazoans Shows Deep Conservation of Cytoplasmic Tyrosine Kinases and Multiple Radiations of Receptor Tyrosine Kinases. Science Signaling 5, ra35.  DOI: 10.1126/scisignal.2002733