Alternative translation initiation produces synaptic organizer proteoforms with distinct localization and functions

Area of Science:

• Molecular Biology
• Neuroscience
• Genetics

Background:

• Many messenger RNAs (mRNAs) possess multiple translation initiation sites (TIS), but the functional relevance of alternative TIS and their protein isoforms (proteoforms) is largely unknown.
• Neuronal pentraxin receptor (NPR) mRNA is a key player in neuronal function, and its regulation is critical for synaptic plasticity.

Approach:

• Investigated alternative translation initiation at CUG and AUG TIS in NPR mRNA.
• Analyzed the impact of neuronal activity and RNA secondary structure on proteoform abundance.
• Examined the functional consequences of altered NPR proteoform ratios on AMPA receptor clustering and mouse learning behaviors.

Key Points:

• Alternative TIS in NPR mRNA generate two distinct proteoforms with different N-terminal signal sequences.
• The downstream AUG initiation site converts the transmembrane domain into a signal peptide, promoting NPR secretion.
• Altering the ratio of NPR proteoforms, not total abundance, affects AMPA receptor levels in interneurons and influences learning.

Conclusions:

• Alternative TIS usage provides plasticity in N-terminal signal sequences, diversifying protein localization and function.
• This mechanism is potentially widespread, affecting other synaptic organizers like C1q-like proteins.
• Regulation of proteoform ratios offers a novel layer of control over synaptic function and behavior.