Key result
Ground squirrel cardiac muscle expresses a single 115 kDa obscurin isoform lacking giant or seasonal variants.
A 115 kDa low-molecular-weight isoform of obscurin was identified in the striated muscles of the long-tailed ground squirrel, with no seasonal variations observed.
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Unlikely to alter clinical management of cardiomyopathy; challenges necessity of giant obscurin isoforms for mammalian striated muscle function.
Polyclonal antibodies specific to the N-sequence (76–289 aa) of obscurin of the long-tailed ground squirrel (Urocitellus undulatus) were used to study the isoform composition of this protein in two striated muscles: the myocardium of the left ventricle and M. gastrocnemius medialis. One low-molecular-weight isoform of obscurin with a molecular weight of 115 kDa has been identified. No other isoforms of obscurin, including giant A- and B-isoforms, have been detected. Seasonal changes in the levels of the low-molecular-weight obscurin isoform visualized in the cardiac and skeletal muscles of long-tailed ground squirrels were not observed. Further research could focus on sequencing the obscn gene of long-tailed ground squirrels and analyzing obscurin transcripts to obtain antibodies specific to the giant isoforms of this protein.
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Uryupina et al. (2025) studied this question. A single 115 kDa isoform of obscurin was identified in the cardiac and skeletal muscles of long-tailed ground squirrels, with no giant isoforms or seasonal changes detected.
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