NOVA1 Promotes SMN2 Exon 7 Splicing via Binding the UCAC Motif and Increases SMN Protein Expression

Abstract Spinal muscular atrophy (SMA) is a rare hereditary neuromuscular disease with high lethality rate in infants. Homologous genes SMN1 and SMN2 were reported to be SMA pathogenic factors. Studies showed that high inclusion of SMN2 exon 7 increased SMN expression which in turn ameliorated the severity of SMA. The inclusion rate of SMN2 exon 7 was higher in neural tissues than that in non-neural tissues. Expression of splicing factors that regulate inclusion of SMN2 exon 7 were significantly increased in neural tissues compared to non-neural ones. A positive correlation was checked between expression of neuro-oncological ventral antigen 1(NOVA1) and SMN in central nervous system. In addition, reduced number of neurons in the spinal cord anterior horn was determined by Nissl staining in SMA mice from postnatal day 1 to 7 continuously. Meanwhile, NOVA1 was presented in motor neurons and gradually decreased as SMA ongoing. Moreover, SMN2 exon 7 inclusion and protein level were enhanced by overexpressing NOVA1, while the enhancement was reversed when NOVA1 knockdown in vitro. Finally, the “YCAY” motif (Y is pyrimidine, U or C) was located in the exon 7 of SMN2 and was critical for NOVA1 binding and promoting the inclusion of exon 7. Mutagenesis experiments revealed that CA was essential for the exon 7 inclusion while less influence was detected by changing order of Y in the motif. Collectively, NOVA1 interacted with “YCAY” motif in exon 7 of SMN2 and thus enhanced the inclusion of exon 7 in SMN2 which in turn increased the level of SMN protein. Our data may provide new insights into the treatment of SMA disease.