Annexin A7 Enhances TIA1 Axon Trafficking to Counteract Pathological Aggregation in Neurons
To characterize the mRNA composition of retrograde TIA1-containing RNPs in axons, we cultured ANXA7 knockdown and control neurons in Boyden chambers to isolate and extract RNA from axons. We then sequenced and compared the axonal mRNAs from both groups, identifying 232 transcripts with significantly increased abundance after ANXA7 knockdown. We validated three transcripts with known neuronal functions, Ryk, Neurod2, and Car7, by reverse transcription-quantitative PCR (RT-qPCR) and examined the abundance of Ryk in axons of cultured hippocampal and cortical neurons using single molecule FISH (smFISH) and found that, in axons of both neuron types, knockdown of ANXA7 significantly increased the density of Ryk mRNA puncta compared to controls. Expression of ANXA7-res restored axonal Ryk mRNA levels to those of controls, confirming the role of ANXA7 in regulating Ryk mRNA axonal bundance. These results indicate that ANXA7-dependent retrograde axon trafficking delivers specific axon-derived mRNAs, such as Ryk, contributing to the dynamic regulation of axon growth in response to morphogens.