The Origin and Evolution of Synapses

Question 1

What is a protosynapse? What is its significance?

Answer 1

ancestoral molecular machinery that existed in unicellular organisms

existed before the evolution of neurons

challenges existing views on the origins of the brain

Question 2

How should we study evolution of the brain?

Answer 2

examine the phylogeny of the molecular components of the synapse

Question 3

Define Postsynaptic proteome

Answer 3

the complete set of proteins currently identified at the postsynaptic side of the synapse

Question 4

The fundamental mechanisms of synaptic transmission and plasticity are __________ across a range of animal species

Answer 4

highly conserved

Question 5

What 3 experimental methods have been recently used to study the evolution of the synapse?

Answer 5

proteomics + genomics + molecular phylogenetics

Question 6

What is Proteomics?

Answer 6

studying the protein constituents of the synapse

Question 7

What is MAGUK (Membrane Associated Guanylate Kinase)?

Answer 7

proteins that act as scaffolds for the clustering of receptors, ion channel,s and associated signalling proteins at postsynaptic sites

traffic NMDA and AMPA receptors to the synapse

Question 8

Define Ursynapse

Answer 8

the last common ancestor of all synapses

the platform from which diversity of synaptic proteins between different organisms and different types of synapses has evolved

Question 9

Define Protosynapse

Answer 9

the synaptic components that were present before the emergence of synapses and most likely contributed to their evolution

Question 10

Name 2 protosynaptic organisms (organisms in which the protosynaptic mechanisms have been conserved)

Answer 10

yeast and amoeba

Question 11

What two protosynaptic mechanisms were found in Yeast and Ameoba that still play a fundamental role in synaptic transmission in animals today?

Answer 11

PMCA (plasma membrane calcium ATPase) and PKC (protien kinase C)

Question 12

Who is the closest unicellular relative of mulitceullular metazoans?

Answer 12

Choanoflagellates

Question 13

Name the multicellular organism that lacks a nervous system that is a candidate for identification of protosynaptic components?

Answer 13

Porifera (sponges)

Question 14

Who are Bilaterians? Name the two major divisions of this phylum

Answer 14

clade of animals who exhibit bilateral symmetry and possess complex nervous systems

2 major division of Phylum Bilatera:

• protostomes
• deuterostomes

Question 15

Protosynaptic proteins represent a pre adaptation that later _____________ for synaptic function and may have contributed to development of ____________

Answer 15

co-opted, the first synapses

Question 16

What is a pitfall that has accompanied the evolution of human behaviour?

Answer 16

positive selection of synaptic proteins has lead to increased human susceptibility to psychiatric diseases

Question 17

Could synapses have existed before axons and dendrites? explain.

Answer 17

yes. synapses might have evolved before axons and dendrites.

an organism with a small number of neurons wouldn’t need axonal projections for neuron to neuron communicaiton

Question 18

why is snypase formation an exception to the general rule that: “Ontogeny recapitulates phylogeny”?

Answer 18

synapses evolved before axons and dendrites

Question 19

Explain the “Synapse-First Model”

Answer 19

the evolution of synapses lead to the evolution of neurons

this is because a neuron is defined by its synaptic connections, and therefore, the synapse must exist first

Question 20

Name some future improvements that can be made in the study of synaptic evolution?

Answer 20

• studies should be expanded to include all presynaptic and postsynaptic proteins
• loss-of-function experiments should be done on ancient and mammalian specific genes in order to determine their physiological function
• Gain-of-function studies should be done on organisms who lack synapses in order to determine what combinations of synaptic proteins resulted in the origin of the synapse
• current studies mostly use mice as subjects. human subjects should be used in the future