# Identification of CaVβ1 Isoforms Required for Neuromuscular Junction Formation and Maintenance

## TL;DR

This study identifies specific CaVβ1 isoforms involved in forming and maintaining neuromuscular junctions in muscle development and repair.

## Contribution

The study reveals novel developmental and functional roles of CaVβ1 isoforms in neuromuscular junction formation and maintenance.

## Key findings

- CaVβ1 isoform expression is developmentally regulated through promoter activation.
- CaVβ1A and CaVβ1E contribute to neuromuscular junction formation and maturation.
- Nerve injury triggers re-expression of embryonic CaVβ1 isoforms in adult muscle.

## Abstract

Voltage-gated Ca2+ channels (VGCCs) are regulated by four CaVβ subunits (CaVβ1–CaVβ4), each showing specific expression patterns in excitable cells. While primarily known for regulating VGCC function, CaVβ proteins also have channel-independent roles, including gene expression modulation. Among these, CaVβ1 is expressed in skeletal muscle as multiple isoforms. The adult isoform, CaVβ1D, localizes at the triad and modulates CaV1 activity during Excitation–Contraction Coupling (ECC). In this study, we investigated the lesser-known embryonic/perinatal CaVβ1 isoforms and their roles in neuromuscular junction (NMJ) formation, maturation, and maintenance. We found that CaVβ1 isoform expression is developmentally regulated through differential promoter activation. Specifically, CaVβ1A is expressed in embryonic muscle and reactivated in denervated adult muscle, alongside the known CaVβ1E isoform. Nerve injury in adult muscle triggers a shift in promoter usage, resulting in re-expression of embryonic/perinatal Cacnb1A and Cacnb1E transcripts. Functional analyses using aneural agrin-induced AChR clustering on primary myotubes demonstrated that these isoforms contribute to NMJ formation. Additionally, their expression during early post-natal development is essential for NMJ maturation and long-term maintenance. These findings reveal previously unrecognized roles of CaVβ1 isoforms beyond VGCC regulation, highlighting their significance in neuromuscular system development and homeostasis.