Fig 4.

Normal motor neurons express remarkably lower levels of full-length SMN2 mRNA than non-motor neurons due to inefficient exon 7 splicing. (A) Schematic representation (top left) and Nissl-stained image (bottom left) of a transverse section of the mouse spinal cord. Nissl-stained images of the ventral horn area of the spinal cord before (top right) and after (bottom right) laser capture microdissection (LCM) of motor neurons are shown. (B) Validation of LCM motor neurons. Real-time RT-qPCR analysis of the expression ofAtp6, ChAT, and GFP mRNAs relative to GAPDH mRNA in LCM motor neurons (MNs) and LCM non-motor neurons (non-MNs) from the spinal cord of normal mice (Smn^+/−; SMN2^+/+; SMNΔ7^+/+; GFP^+/−) at postnatal day 6. (C) Normal motor neurons express much less full-length SMN2 mRNA than do non-motor neurons. Real-time RT-qPCR analysis of the expression of total (FL+Δ7; SMN2_TOT) and full-length (FL; SMN2_FL) SMN2 mRNAs relative to GAPDH mRNA in LCM MNs and LCM non-MNs. (D) Exon 7 inclusion is less efficient in normal motor neurons than in non-motor neurons. Normalized exon 7 inclusion was measured by real-time RT-qPCR analysis of the expression of full-length (SMN2_FL) relative to total (SMN2_TOT) SMN2 mRNAs in LCM MNs and LCM non-MNs. Values represent means and SEM from independent experiments (n=8; *, P < 0.05; **, P < 0.01; ***, P < 0.001).