# Novel insights into the molecular mechanisms of LGMDD2: role of TNPO3 in experimental cell and zebrafish models

## TL;DR

This study explores how mutations in the TNPO3 gene cause LGMDD2, a rare muscular dystrophy, using cell and zebrafish models to reveal its role in muscle development.

## Contribution

The study introduces novel experimental models to demonstrate TNPO3's role in myogenesis and LGMDD2 pathogenesis.

## Key findings

- TNPO3 mutations disrupt normal myogenic commitment in both cell and zebrafish models.
- Expression of myogenesis-related genes is altered in models with mutated TNPO3.
- The zebrafish model shows morphological and behavioral changes consistent with LGMDD2.

## Abstract

Transportin 3 (TNPO3) is a nuclear carrier for serine/arginine-rich proteins which are essential for mRNA splicing and metabolism. Mutations in the TNPO3 gene result in a protein with an extended C-terminal domain, leading to the onset of LGMDD2, a rare form of limb girdle muscular dystrophy. To investigate the role of TNPO3 in skeletal muscle and the pathogenic mechanism underlying LGMDD2, we develped both in vitro and in vivo models of the disease. The in vitro model was established using the C2C12 cell line, transfected with plasmids encoding either the wild-type (WT) or mutated (MUT) human TNPO3 (hTNPO3). For the in vivo model, we microinjected zebrafish (Danio rerio) embryos with mRNAs encoding WT or MUT hTNPO3. We analyzed the expression patterns of myogenesis-related genes, muscle-specific genes, myomiRNA and genes strictly related to the disease. These analyses were complemented by protein expression studies, morphological assessments in both models, and behavioral assays to validate the LGMDD2 zebrafish model. Our results demonstrate a key role for TNPO3 in regulating myogenesis in both models and reveal that the TNPO3 mutation disrupts normal myogenic commitment, supporting its contribution to LGMDD2 pathogenesis. Overall, this study represents a significant advance in understanding the role of TNPO3 in skeletal muscle biology and the molecular basis of LGMDD2.

The online version contains supplementary material available at 10.1007/s00018-025-05954-9.