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Foot protein isoforms are expressed at different times during embryonic chick skeletal muscle development
J L Sutko1, J A Airey, K Murakami
1Department of Pharmacology, University of Nevada, Reno 89557.
Insights
The study reveals that alpha and beta foot proteins in chick muscle develop alongside ryanodine binding, suggesting roles in calcium channels and muscle differentiation.
Area of Science:
- Muscle Biology
- Developmental Biology
- Cellular Physiology
Background:
- Triad junctional foot proteins are critical for muscle excitation-contraction coupling.
- Understanding their developmental expression is key to elucidating muscle function.
Purpose of the Study:
- To investigate the temporal expression patterns of alpha and beta foot protein isoforms in embryonic chick pectoral muscle.
- To correlate protein expression with functional markers like ryanodine binding.
Main Methods:
- [3H]ryanodine binding assays on muscle homogenates.
- Immunodetection using isoform-specific antibodies.
- Analysis of protein distribution during muscle development.
Main Results:
- [3H]ryanodine binding and both foot protein isoforms increase significantly around hatching.
- Alpha isoform is detected early (E10), while beta isoform appears later (E15).
- A distinct high molecular weight polypeptide is present early but diminishes during development.
Conclusions:
- Alpha and beta foot proteins are expressed differentially during muscle development.
- Oligomeric forms of alpha and beta isoforms bind ryanodine, suggesting roles as calcium channels.
- Foot protein expression coincides with myofibril assembly and muscle differentiation events.
Abstract:
We have investigated the time course of expression of the alpha and beta triad junctional foot proteins in embryonic chick pectoral muscle. The level of [3H]ryanodine binding in muscle homogenates is low until day E20 of embryonic development, then increases dramatically at the time of hatching reaching adult levels by day N7 posthatch. The alpha and beta foot protein isoforms increase in abundance concomitantly with [3H]ryanodine binding. Using foot protein isoform-specific antibodies, the alpha foot protein is detected in a majority of fibers in day E10 muscle, while the beta isoform is first observed at low levels in a few fibers in day E15 muscle. A high molecular weight polypeptide, distinct from the alpha and beta proteins, is recognized by antifoot protein antibodies. This polypeptide is observed in day E8 muscle and declines in abundance with continued development. It appears to exist as a monomer and does not bind [3H]ryanodine. In contrast, the alpha isoform present in day E10 muscle and the beta isoform in day E20 muscle are oligomeric and bind [3H]ryanodine suggesting that they may exist as functional calcium channels in differentiating muscle. Comparison of the intracellular distributions of the alpha foot protein, f-actin, the heavy chain of myosin and titin in day E10 muscle indicates that the alpha foot protein is expressed during myofibril assembly and Z line formation. The differential expression of the foot protein isoforms in developing muscle, and their continued expression in mature muscle, is consistent with these proteins making different functional contributions. In addition, the expression of the alpha isoform during the time of organization of a differentiated muscle morphology suggests that foot proteins may participate in events involved in muscle differentiation.