Innovations in Molecular Biotechnology

ABSTRACT

Calsequestrin (CASQ), a high-capacity calcium-binding protein localized in the sarcoplasmic reticulum (SR), was first identified in rabbit skeletal muscle in 1971. Initially considered a passive calcium buffer, subsequent studies over the past three decades have elucidated the multifunctional nature of the skeletal muscle isoform, CASQ1. In addition to maintaining intraluminal SR calcium concentrations essential for muscle contraction and relaxation, CASQ1 acts as a dynamic calcium sensor, modulating calcium release during excitation-contraction coupling. It also contributes structurally to the organization and stabilization of the terminal cisternae of the SR. Skeletal muscle movement and posture maintenance rely on fluctuations in calcium ion (Ca²?) levels within the cytosol of myotubes, the cells that make up skeletal muscle tissue. A brief increase in intracellular calcium (Ca²?) serves as an essential mediator between electrical signals moving through the transverse (T)-tubule membrane and the triggering of muscle contraction, termed as excitation?contraction coupling. Recent evidence suggests CASQ1 may influence reverse-directional calcium influx from the extracellular milieu, implicating it in broader calcium homeostasis mechanisms. Dysregulation or mutation in the CASQ1 gene has been associated with various skeletal muscle pathologies, emphasizing its clinical relevance. In this study, we investigated the expression pattern of the CASQ1 gene in the soleus muscle of the rabbit, a muscle predominantly composed of slow-twitch (Type I) fibres critical for postural stability. Our analysis adds to the growing body of evidence characterizing fibre-type-specific expression of calcium-regulatory proteins. This study is limited to gene expression profiling in a single muscle type and species. Functional characterization at the protein level and cross-species comparisons were not within the scope of this investigation. The objective of this study was to elucidate the expression profile of CASQ1 in rabbit soleus muscle, thereby contributing to the understanding of its role in calcium signalling and muscle fibre specialization. These findings may facilitate future research on CASQ1-related myopathies.

KEYWORDS

1. Calsequestrin (CASQ1)
2. Rabbit soleus muscle
3. Skeletal muscle
4. Calcium homeostasis
5. Sarcoplasmic reticulum
6. RT-PCR
7. Gene expression