Abstract Body: Introduction/Background
The sarcoplasmic reticulum (SR), a specialized form of endoplasmic reticulum, is crucial for muscle contraction as it regulates calcium storage, release, and uptake. The structure of the SR is organized during the later stage of myogenesis, coinciding with the organization of contractile proteins into sarcomeres. During development, the SR is thought to gradually elongate via its association with contractile and anchoring proteins, yet the precise mechanisms governing SR network formation remain poorly understood.
Small ankryn 1 (sAnk1), a muscle-specific byproduct of the ANK1 gene, is an integral SR protein. In mature striated muscle, sAnk1 predominantly localizes to the M-band and, to a lesser extent, at the Z-disk. sAnk1 directly interacts with obscurin, phospholamban (PLN), sarcolipin (SLN) and SERCA, suggesting a role in Ca²⁺ homeostasis. Partial knockdown of sAnk1 in skeletal muscle results in altered longitudinal SR structure, akin to what is observed in obscurin knockout muscles. Thus, sAnk1 appears to play a role in SR network organization, perhaps through its association with obscurin. Our lab was also the first to identify a post-translational modification that occurs within sAnk1, a phosphorylation event at Serine 55.
Hypothesis
Herein, we investigate the role of sAnk1 in SR network formation during striated muscle myogenesis.
Methods
Utilizing Western Blots, subcellular fractionation, chromatin immunoprecipitation, and immunofluorescence we evaluated the temporal expression and subcellular localization of total sAnk1 and phosphorylated sAnk1 (phospho-Serine55) in mouse myoblasts throughout the process of myogenic differentiation.
Results
Intriguingly, subcellular fractionation revealed the presence of sAnk1 in nuclear and chromatin-bound fractions. Chromatin immunoprecipitation further demonstrated that sAnk1 specifically binds to Histone 3. During myogenesis, the proportion of sAnk1 and phospho-sAnk1 that is chromatin-bound decreases, while sAnk1 expression in cytosolic and membrane fractions increases.
Conclusion(s)
This study is the first to identify the presence of sAnk1 in the nucleus, where it associates with chromatin and Histone 3, specifically. The observed decrease in chromatin-bound sAnk1 during myogenesis suggests a potential transcriptional or epigenetic role in regulating SR formation.