Z‐band and M‐band Titin Splicing and Regulation by RBM20 in Striated Muscles

Abstract

Titin (TTN) has multifunctional roles in sarcomere assembly, mechanosignaling transduction and muscle stiffness. TTN splicing generates variable protein sizes that are associated with its functions. Therefore, understanding TTN splicing is important to develop novel treatment for titin‐based diseases. The I‐band TTN splicing and regulation by RBM20 have been extensively studied. However, the Z‐ and Mband splicing and regulation remain poorly understood. Herein, we aimed to define the Z‐ and M‐band splicing in striated muscles, and also determine whether RBM20 regulates the Z‐ and M‐band splicing. Our data discovered four new Z‐band TTN splicing variants, and one of them dominates in mouse, rat, sheep and human heart. Frog and chicken hearts express only one variant. In skeletal muscles, three new Z repeats were detected, and variant with Zr4–6 skipping dominates in the fast muscles, whereas Zr4 skipping dominates in the slow muscle. No developmental changes were detected in the Z‐band. In the M‐band, two new variants were discovered with alternative 3′ splice site in exon363 (Mex5) and alternative 5′ splice site in intron362. However, only sheep heart expresses two new variants, while other species express only one variant with Mex5+. Skeletal muscles express all three M‐band variants with altered ratios of Mex5+ to Mex5−. Lastly, we revealed that RBM20 does not regulate the Z‐and M‐band splicing in the heart, but does in skeletal muscles. Taken together, we characterized the Z‐ and M‐band splicing and provided the first evidence of the role of RBM20 in the Z‐ and M‐band TTN splicing.Support or Funding InformationThis work was supported by the National Institute of Health/National Institute of General Medical Sciences [NIGMSP20GM103432]; the BGIA from the American Heart Association [16BGIA27790136 to WG]; the USDA National Institute of Food and Agriculture [Hatch project 1009266 to WG]; NICHD 1R01HD070096‐01A1 (SPF and PWN). Ying Ge would like to acknowledge NIH R01 HL109810 and HL096971.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.