library_construction_protocol: Brain and spinal cord were collected from control and SMA embryos at E14.5, snap frozen and then stored at -80℃ until used. Cytoplasmic lysates were prepared as it follows. Briefly, the tissues were pulverised with a sterile pestle and mortar in liquid nitrogen, and then 400-800 μL of tissue was added to ribosome lysis buffer (10mM Tris-HCl pH 7.5, 10mM MgCl2, 10mM NaCl, 1% w/V TritonX-100, 5 U/mL DNAseI, 800 U/ml RiboLock RNAse Inhibitor, 1mM DTT, 200μg/mL cycloheximide, 1% w/V Na-deoxycholate). To facilitate cell lysis, lysates were incubated on ice for 17-20 minutes followed by centrifuging twice at 12,000 rpm for 10 min at 4°C to remove tissue debris, mitochondria, and nuclei. Supernatants was measured for the 260nm absorbance, the final NaCl salt concentration of the lysate was adjusted to a final salt concentration of 100 mM. Ribosome purification was achieved by treating lysates with 10 U/Abs RNAse at room temperature for 45 minutes followed by addition of 5μL of SUPERase-In RNase inhibitor (Thermo Fisher Scientific) to halt the reaction. Lysates were loaded onto 13.2 mL polyallomer ultracentrifuge tubes (Beckman) containing a 10%-40% (w/v) linear sucrose gradient (10mM Tris-HCl ph7.5, 10mM MgCl2, 10mM NaCl). The fraction was then used for RNA purification using the phenol/chloroform protocol. Ribosome-protected fragments (RPFs) measuring 28-32bp were separated and purified using a 15% Urea-TBE gel. After RNA extraction from the gel, RPFs were then dephosphorylated using 120U T4 polynucleotide kinase (New England Biolabs #M0201S) and 20U of SUPERase-InTM Rnase inhibitor in T4 PNK polynucleotide kinase buffer (New England Biolabs) at 37 °C for 1 hour followed by 10 minutes incubation at 70 °C to inactivate the enzymes. After RPFs purification, the libraries were prepared. Experiments were performed in triplicate. Libraries from E14.5 brain and spinal cord tissues of Taiwanese mouse embryos were sequenced at the CIBIO NGS facility of the University of Trento, Italy, using an Illumina NovaSeq6000 system.