Temporal Regulation of Localized mRNA Translation in Regenerating Axons
Target Investigator:
Soonmoon Yoo, PhD
Senior Research Scientist
Mentors: Robert W Mason, Ph.D.
Robert Akins, Ph.D.

The long-term goal of this research is to understand the specificity of axonal mRNA translation during neural repair and regeneration.  Many recent studies, including work from our lab, show that proteins are actively synthesized in developing and regenerating axons.  This localized protein synthesis facilitates axonal growth and regeneration following injury, and is regulated by extracellular stimuli.  Despite these recent advances, we still have little knowledge of how intracellular signaling cascades regulate local translation at the level of individual mRNAs.  Several lines of evidence indicate untranslated regions (UTRs) of mRNAs encode information that determines their subcellular localization and translation.  Changes in intracellular Ca2+ levels ([Ca2+]i) have been suggested to contribute to membrane sealing, retrograde signaling, and growth cone formation in injured axons.  Ca2+ is also known to alter activity of the translational machinery.  These observations have led me to hypothesize that intra-axonal cation signaling mechanisms converge on the localized protein synthesis machinery to specifically regulate the translation of individual mRNAs in injured axons.  I will focus on axonal mRNAs that encode injury-response (Importin-b1, RanBP1) and growth-associated proteins (GAP-43).  In preliminary studies, we use a bioreporter system to show that intra-axonal translation of GAP-43 mRNA is active in low [Ca2+]i, in contrast to our previous studies showing that translation of another axonal mRNA is active in high [Ca2+]i.  The specific aims outlined below focus on understanding how cation-mediated neuronal signal transduction pathway(s) regulate axonal mRNA translation.

Specific Aim 1:  Axonally transported mRNAs encoding injury-response and growth-associated proteins contain region(s) that impart translational regulation to these mRNAs. 

Sub-Aim 1A.  Determine if UTR(s) of Importin-b1, RanBP1, and GAP-43 mRNAs are necessary for regulating their translation in axons.

Sub-Aim 1B.  Determine if the cis-elements within UTRs of Importin-b1, RanBP1, and GAP-43 mRNAs are sufficient for stimulus-dependent translation in axons.

Specific Aim 2The specificity of axonal protein synthesis is regulated by local cationic changes to support stimulus-response coupling in the axon. 

Sub-Aim 2A.  Identify the origin of mobilized axoplasmic Ca2+ that has a coordinating role in regulation of local protein synthesis.

Sub-Aim 2B.  Examine the roles of Ca2+-stimulated adenylyl cyclase, calpain, and calmodulin-dependent protein kinases in the regulation of localized protein synthesis.