Summary lecture evolution of the brain and synapse (neurosciences)

Evolution of the brain and synapse
 You know the meaning of the terms homolog, ortholog and paralog and you can use them correctly.
 You can describe the evolution of the synapse and you know which critical synapse gene arise in
different species.
 You can analyse the differences between brains of humans and other species.

Human species has highly developed brain. This lecture focuses on how do who get such a brain, what
makes our brain special.

Why do we have a nervous system? An information exchange system in multicellular organisms. Relay
system to exchange information in complex organism. Cells in different parts need to know what they are
doing, need to communicate. Our nervous system can detect external signals and change its behaviour ->
huge evolutionary advantage.

Information exchange is mediated by neurons:

 Receives, sends, transmits information,
forms networks, process information,
electrical signals; action potentials, has
axons and dendrites.
 Synapse is highly complex functional
structure; pre- and post-synapse. How did
it arise?




Paper Ryan & Grant; The origin and evolution of synapses. Main objectives of paper;

 Proteomic and genomic research of the synapse.
 Protosynapse - ursynapse - synapse
 Postsynaptic proteins are present in protosynaptic organisms, they register external stimuli.
 Sponges (multicellular organism without a nervous system) en choanoflagellate (single cellular
organism that forms colonies) are model systems to investigate the origin of the synapse.
 Glutamate receptors (ionotropic) mark the first organisms with a nervous system.
 Gene duplication (paraloges) in complex organisms.
 Proteins with many interactions are likely being conserved in evolution.
 Synapses have appeared before dendrites or axons: without synapses these have no function.
Hence, no synapse no neuron no nervous system.

, Ursynapse -> most primitive functional synapse, before that no synapses (protosynaptic). Division
eumetazoans and metazoans. Basic principles of how synapses work are present in ursynapse.

Evolution as research tool

 Homolog: genes or proteins that share a common ancestor.
- Ortholog: genes and proteins that share a common function or structure in different species.
- Paralog: multiple variants of a similar protein or gene in one species.

The protosynapse: protein complexes in organisms without a nervous system. S. cerevisae (yeast) and D.
discoideum (amoeba) express calcium pumps and protein kinase C, which are important for synapse
function. Information exchange with outside world and inside cell. S. cerevisae contains 25% post-synaptic
density (PSD) ortholog genes, that regulate its response to external stimuli.

Choanoflagellata a complex single cell organism. It likes to life in clumps/colonies. New protosynapse genes:

 Cadherins and catenins: cell adhesion (tie cells together, cause like to life in colonies)
 Tyrosine kinase receptors: response to external stimuli (tyrosine kinase receptor; synaptic plasticity
in later organisms)

Demospongiae; most complex organism that does not have a nervous system. Demospongiae or the ‘normal
sponge’ can;

 Change its size
 Move flagella
 Contract (due to contact)

No nervous system. But other types of specialized cells, that do signal to each other but do not form
synapses. New protosynapse genes:

 Neurexin
 GABA receptors
 Metabotropic glutamate receptors
 Ca/calmodulin-dependent kinase (CaMKII) important for synaptic plasticity