SCIENCE SIGNALING

Facilitating Multicellularity

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Science  01 Aug 2008:
Vol. 321, Issue 5889, pp. 613
DOI: 10.1126/science.321.5889.613c

Tyrosine kinase signaling plays an integral role in intercellular communication in multicellular animals (metazoans). There are three essential molecular components: protein tyrosine kinases (PTKs), protein tyrosine phosphatases (PTPs), and SH2 domains (phosphotyrosine-binding modules). Once thought to be limited to metazoans, these components have been identified in choanoflagellates (such as the recently sequenced Monosiga brevicollis), their closest unicellular relatives. Manning et al. and Pincus et al. have surveyed the Monosiga genome for genes encoding PTKs, PTPs, and SH2 domains and report a large number, most of which have no metazoan orthologs. For example, only eight of the PTKs identified by Manning et al. have metazoan orthologs, indicating that the expansion of the PTP-, PTK- and SH2-containing protein families occurred after the ancestral lineage had split. Both lineages have evolved similar functionality through domain shuffling. For example, receptor tyrosine kinases with cysteine-rich motifs appear in both lineages. Fungi and slime molds, eukaryotes lying outside the metazoan-choanoflagellate lineage, have PTPs and SH2-containing proteins but not PTKs, and Pincus et al. point out that having only these two components could be advantageous because some serine/threonine kinases, which fungi and slime molds have in abundance, do perform tyrosine phosphorylation inefficiently. — AMV

Proc. Natl. Acad. Sci. U.S.A. 105, 9674; 9680 (2008).

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