Professor Ken Taylor - Florida State University - USA

Professor Ken Taylor

The striated muscle myosin filament structure has defied detailed understanding for decades. Striated muscle developed early in the evolution of life on earth. Invertebrates appear in the fossil record at over 600 Mya. Vertebrates appear somewhat later between 485-444 Mya. The earliest evidence of a striated muscle is from a jelly fish fossil dated 560 Mya. The myosin filaments of invertebrate striated muscle are highly variable in structure coming in widely different lengths and rotational symmetries from C4-C7. On the other hand, so far as is known, the thick filaments of vertebrates have a single structure with a length of 1.6 mm and a rotational symmetry of C3. The inherent order in a biological structure is a key parameter for its detailed understanding. The most highly ordered striated muscles come from the indirect flight muscles of four insect orders, Hemiptera, Diptera, Hymenoptera and Coleoptera. On the premise that these highly specialized muscles will be quite similar, we have examined flight muscle thick filaments from three of these orders and found that no two were exactly alike and some were quite different. The greatest similarity appears to be in the arrangement of myosin tails in the filament backbone which determine the helical symmetry of the filament. However, pronounced differences appear among the non-myosin proteins. Some species, most notably Drosophila melanogaster, even change their thick filament structure as the flies age. What advantage does this capability provide the animal? The other aspect of striated muscle structure is how the molecules change structure or even arrangement when activated. This has been studied for decades using various techniques but now appears to be accessible in detail by the developing techniques of Focused Ion Beam milling and cryoelectron tomography. The main problems are how to freeze an active muscle at given time points after stimulation, a sort of time resolved cryoelectron tomography. I will discuss a few past results obtained from frozen, active muscle and some possible future directions that might unlock this question.