High expression level of Tra2-β1 is responsible for increased SMN2 exon 7 inclusion in the testis of SMA mice.

Yu-Chia Chen,Yuh-Jyh Jong,Jan-Gowth Chang,Chung-Yee Yuo,Ting-Yuan Liu,Thomas H Gillingwater

doi:10.1371/journal.pone.0120721

Abstract

Spinal muscular atrophy (SMA) is an inherited neuromuscular disease caused by deletion or mutation of SMN1 gene. All SMA patients carry a nearly identical SMN2 gene, which produces low level of SMN protein due to mRNA exon 7 exclusion. Previously, we found that the testis of SMA mice (smn−/− SMN2) expresses high level of SMN2 full-length mRNA, indicating a testis-specific mechanism for SMN2 exon 7 inclusion. To elucidate the underlying mechanism, we established primary cultures of testis cells from SMA mice and analyzed them for SMN2 exon 7 splicing. We found that primary testis cells after a 2-hour culture still expressed high level of SMN2 full-length mRNA, but the level decreased after longer cultures. We then compared the protein levels of relevant splicing factors, and found that the level of Tra2-β1 also decreased during testis cell culture, correlated with SMN2 full-length mRNA downregulation. In addition, the testis of SMA mice expressed the highest level of Tra2-β1 among the many tissues examined. Furthermore, overexpression of Tra2-β1, but not ASF/SF2, increased SMN2 minigene exon 7 inclusion in primary testis cells and spinal cord neurons, whereas knockdown of Tra2-β1 decreased SMN2 exon 7 inclusion in primary testis cells of SMA mice. Therefore, our results indicate that high expression level of Tra2-β1 is responsible for increased SMN2 exon 7 inclusion in the testis of SMA mice. This study also suggests that the expression level of Tra2-β1 may be a modifying factor of SMA disease and a potential target for SMA treatment.

Highlights

Spinal muscular atrophy (SMA) is an autosomal recessive disease characterized by the loss of lower motor neurons and atrophy of muscles
We examined the SMN2 mRNA splicing and SMN protein expression in several tissues of type 3 SMA mice, including brain, spinal cord, heart, liver, lung, stomach, kidney, spleen, intestine, muscle, tail, testis in male mice, and ovary in female mice
Among the tissues we examined, we found that the testis expressed high level of SMN2 full-length (FL) mRNA (Fig. 1A and see S1 Fig. for qRT-PCR result) and SMN protein (Fig. 1B)

Summary

Introduction

Spinal muscular atrophy (SMA) is an autosomal recessive disease characterized by the loss of lower motor neurons and atrophy of muscles. According to age of onset and its severity, SMA. SMN2 Splicing in the Testis of SMA Mice is categorized into three main types (type I—III) and two subtypes (type 0 and type IV) [1,2]. SMA is the second most common autosomal recessive disease and the most common genetic cause of infant mortality [3]. SMA is caused by deletions or mutations of survival motor neuron 1 (SMN1) gene. All SMA patients carry a nearly identical SMN2 gene. The nucleotide transition causes exon 7 exclusion in most SMN2 mRNA [5,6,7,8]

Methods

Results

Conclusion