SB-431542

Axial rotation (AR), a morphogenetic movement that reshapes the body axis, is widely observed in chordates, including mice and rats. AR involves complex three-dimensional deformations; however, its geometric characteristics and regulatory mechanisms remain poorly understood. Here, using the chordate Ciona robusta (Ciona intestinalis type A), we demonstrate that AR consists of two differentially regulated components-leftward bending and clockwise twisting along the anterior-posterior axis. A comparison between chorionated and dechorionated embryos revealed that dechorionation randomized the bending direction, while twisting remained consistently clockwise. Inhibition of TGF-β signaling with SB431542 randomized both deformations. Quantitative analysis of twisting angles indicated uniform clockwise twisting along the axis, peaking during the tailbud stage and proceeding in the tail region, independent of the tip, trunk, or myofibril patterning. Although overall twisting was reduced under TGF-β inhibition, the tail exhibited disorganized twisting. The sum of absolute twisting-angle differences in every 10 μm remained comparable to the wild type (WT). This suggests that twisting is intrinsically generated, while TGF-β signaling aligns local twisting into a coordinated global direction. Our findings dissected the mechanisms of AR in Ciona and highlight the multilayered regulation underlying the morphogenesis of the chordate body plan and providing a foundation for understanding its biomechanical and molecular bases.

Previous studies have highlighted the significance of RNA-binding proteins and alternative splicing (AS) in the progression of complex diseases, but the specific involvement of AS in heart failure (HF) remains unclear. This study aimed to elucidate the role of RNA-binding motif single-stranded interacting protein 1 (RBMS1), an RNA-binding protein, in the development of HF by regulating AS and its effect on cardiac fibrosis.

The level of RBMS1 was investigated in the hearts of both HF patients and mice. Fibroblast-specific knockout RBMS1 mice were generated to investigate the role of RBMS1 in cardiac fibrosis and HF. Unbiased RNA sequencing and RNA immunoprecipitation combined with RNA pull-down were conducted to identify the downstream effector of RBMS1 in fibroblasts.

RBMS1 expression was increased in murine hearts following myocardial infarction, as well as in the hearts of patients with ischaemic cardiomyopathy and hypertrophic cardiomyopathy. Moreover, RBMS1 levels in the hearts of HF patients were positively associated with cardiac fibrosis. Furthermore, fibroblast-specific ablation of RBMS1 improved cardiac dysfunction by mitigating myocardial fibrosis. Mechanistically, RBMS1 regulated the alternative splicing of LIM domain 7 (LMO7) by binding to intron 19 and splicing out exon 20, resulting in the formation of the LMO7-Δe20 isoform, which thus activated the transforming growth factor (TGF)-β1 pathway by upregulating activator protein 1. More importantly, overexpression of LMO7-Δe20 in mice resulted in cardiac fibrosis and cardiac dysfunction, which was ablated after treatment with TGF-β1 pathway inhibitor SB431542. In addition, SB431542 attenuated the RBMS1-driven fibrogenesis in human cardiac fibroblasts. Strikingly, pharmacologically inhibiting RBMS1 by low-dose nortriptyline or antisense oligonucleotide-mediated RBMS1 deficiency alleviated myocardial fibrosis and improved cardiac function in HF mice.

These findings unveil a critical role of RBMS1 in regulating cardiac fibrosis through controlling the splicing of LMO7 to activate the TGF-β1 pathway. Genetic ablation or pharmacological inhibition of RBMS1 improves cardiac function in mice, suggesting its potential as a therapeutic target for HF.