After considering that tyrosine kinases are crucial to the metazoan way of life, ponder the fact that scientists have recently discovered this circuit to exist in choanoflagellates – a single-celled organism:
By analyzing the recently-sequenced choanoflagellate genome, the researchers discovered another similarity between choanoflagellates and most metazoans–their genetic code caries the markers of three types of molecules that cells use to achieve phospho-tyrosine signaling proteins.
Animals depend on tyrosine phosphorylation to conduct a number of important communications between their cells, including immune system responses, hormone system stimulation and other crucial functions. These phospho-tyrosine signaling pathways utilize a three-part system of molecular components to make these communications possible.
Tyrosine kinases (TyrK) ‘write’ messages between cells by adding phospho-tyrosine modifications, protein tyrosine phosphatases (PTP) are molecules that modify or ‘erase’ these modifications, and Src Homolgy 2 (SH2) molecules ‘read’ these modifications so the recipient cell gets the message.
Without these three molecules to help our cells ‘write,’ ‘read’ and ‘erase’ chemical messages between them, our bodies would never be able to conduct the complex tasks needed to survive such as reproduction, digesting food or even breathing.
Other genome analysis showed that some microorganisms contain some of these molecules in small levels, but never all three. This makes sense considering these organisms don’t need the tools to communicate between cells since they are made up of only one cell. What makes choanoflagellates unique, however, is that they have all three of these molecules. What’s more, they have relatively large quantities of them in amounts commonly seen in larger metazoan organisms.
The researchers conclude that the presence of the full three-component signaling system may have played a role in the development of metazoan organisms whose cells could communicate with each other in complex ways.
Once “these three molecules” were brought together in the ancestors of choanoflagellates, the task of the blind watchmaker would simply be to enhance their expression levels and a crucial door to animal evolution would be swung open. In fact, I’ll add an interesting piece of supporting evidence for this hypothesis in the next entry.