SMN deficiency alters Nrxn2 expression and splicing in zebrafish and mouse models of spinal muscular atrophy.
Spinal muscular atrophy (SMA) is a progressive neurodegenerative disease affecting lower motor neurons. SMA is caused by mutations in the Survival Motor Neuron 1 (SMN1) gene, which result in reduced levels of functional SMN protein. Biochemical studies have linked the ubiquitously expressed SMN protein to the assembly of pre-mRNA processing U snRNPs, raising the possibility that aberrant splicing is a major defect in SMA. Accordingly, several transcripts affected upon SMN deficiency have been reported. A second function for SMN in axonal mRNA transport has also been proposed that may likewise contribute to the SMA phenotype. The underlying etiology of SMA, however, is still not fully understood. Here, we have used a combination of genomics and live Ca(2+) imaging to investigate the consequences of SMN deficiency in a zebrafish model of SMA. In a transcriptome analyses of SMN-deficient zebrafish, we identified neurexin2a (nrxn2a) as strongly down-regulated and displaying changes in alternative splicing patterns. Importantly, the knock-down of two distinct nrxn2a isoforms phenocopies SMN-deficient fish and results in a significant reduction of motor axon excitability. Interestingly, we observed altered expression and splicing of Nrxn2 also in motor neurons from the Smn(-/-);SMN2(+/+) mouse model of SMA, suggesting conservation of nrxn2 regulation by SMN in mammals. We propose that SMN deficiency affects splicing and abundance of nrxn2a. This may explain the pre-synaptic defects at neuromuscular endplates in SMA pathophysiology.
Department of Biological Sciences, National University of Singapore, Singapore 117543, Singapore.
Kelvin
K
See
Preeti
P
Yadav
Marieke
M
Giegerich
Pearl S
PS
Cheong
Martin
M
Graf
Himanshu
H
Vyas
Serene G P
SG
Lee
Sinnakaruppan
S
Mathavan
Utz
U
Fischer
Michael
M
Sendtner
Christoph
C
Winkler
D017398:Alternative Splicing / Q000235:genetics; D000818:Animals; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling; D002478:Cells, Cultured; D004195:Disease Models, Animal; D055785:Gene Knockdown Techniques; D017403:In Situ Hybridization; D061346:Laser Capture Microdissection; D051379:Mice; D008822:Mice, Transgenic; D060172:Morpholinos / Q000235:genetics; D009046:Motor Neurons / Q000378:metabolism; D009134:Muscular Atrophy, Spinal / Q000235:genetics*; D009419:Nerve Tissue Proteins / Q000096:biosynthesis / Q000235:genetics*; D020033:Protein Isoforms / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics; D013116:Spinal Cord / Q000378:metabolism; D055533:Survival of Motor Neuron 1 Protein / Q000235:genetics*; D055540:Survival of Motor Neuron 2 Protein / Q000235:genetics; D015027:Zebrafish
D060172:Morpholinos; D009419:Nerve Tissue Proteins; D020033:Protein Isoforms; D012333:RNA, Messenger; D055533:Survival of Motor Neuron 1 Protein; D055540:Survival of Motor Neuron 2 Protein; C093175:neurexin II; C526474:smn1 protein, zebrafish; D002118:Calcium