Xin expression is observed within muscle satellite cells of regenerating skeletal muscle

Xin is a novel actin‐binding protein whose expression has been demonstrated in the adherens junction complex in developing striated muscles. In the present study, we used microarray and RT‐PCR analysis to demonstrate that Xin is robustly upregulated (>16 fold increase) at 6 and 12 hours following skeletal muscle injury with a decline in expression pattern from 2 days to 14 days post‐injury. In situ hybridization analysis during the early time points of regeneration localize Xin expression to the periphery of the muscle fiber, in the location of the muscle satellite cell population. Expression of Xin within non‐muscle lineages (e.g. neural, hematopoeitic) was not observed. RT‐PCR analysis confirmed the expression pattern of Xin in primary myogenic satellite cell cultures, but not other known stem cell populations. In situ hybridization at later time points of skeletal muscle regeneration (5 and 7 days post‐injury) illustrate Xin expression within newly regenerated myofibres, as well as within the myopathic heart and diaphragm of the mdx mouse. Based on the known interaction of Xin and the actin cytoskeleton and the present findings, we would suggest that the early onset of Xin in response to skeletal muscle injury promotes satellite cell activation. These findings help to define the regulation of the muscle satellite cell population and may prove important in understanding and treating skeletal muscle myopathies.