Layman's guide to synapses

Synaptic components are encoded by specific genes

Most synaptic components are proteins, the blue print of which is stored in form of genes on the chromosomes. If such genes are aberrant (affected by mutation), the synaptic components they encode are affected (non-functional, missing or wrongly positioned). This can have severe consequences for synapse function. The resulting synaptic dysfunction will be inherited, i.e. passed on from generation to generation following the Mendelian rules of inheritance.

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The picture illustrates the relation between genes and synapses in a considerably simplified way. Two different synapse types with respective pre- and postsynaptic terminals are shown. Gene 1 and gene 3 encode distinct structural proteins A and B, respectively, which are differentially produced in the two synapse types (red versus green arrows). Here they contribute to distinct forms of presynaptic specialisations (red versus green structures associated with vesicles). In contrast, gene 2 gives rise to a cell adhesion molecule which is produced in neurons of both synapse types where it is required to establish/maintain synaptic contact. Thus, different synapse types may share certain components, other components equip each synapse type differentially with its specific properties (e.g. excitatory versus inhibitory properties).
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If the product of gene 2 is affected by mutation (stippled X) leading to absence of its gene product (open arrow), both synapse types are structurally and functionally affected, since pre- and postsynaptic terminals loose contact, respectively (double arrows). Thus, defects caused by mutation tell us something about the normal function of the healthy gene product. Mutational defects enable us to determine the genes/components required for specific synapse formation, function or maintenance.
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If gene 1 is affected by mutation (stippled X) leading to absence of its gene product (open arrow), the left but not the right synapse type is structurally and functionally affected (vesicles fail to localise and can no longer fuse). Thus, specific mutations can help to distinguish between different synapse types and to pinpoint the distinct components mediating their type-specific structure and function.

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Many synaptic genes and gene functions are very similar in humans, higher and lower animals >>>