SUMMARY
Masticatory myosin is widely expressed among several vertebrate classes. Generally, the expression of masticatory myosin has been associated with high bite force for a carnivorous feeding style (including capturing/restraining live prey), breaking down tough plant material and defensive biting in different species. Masticatory myosin expression in the largest mammalian order, Rodentia, has not been reported. Several members of Rodentia consume large numbers of tree nuts that are encased in very hard shells, presumably requiring large forces to access the nutmeat. We, therefore, tested whether some rodent species express masticatory myosin in jaw-closing muscles. Myosin isoform expression in six Sciuridae species was examined, using protein gel electrophoresis, immunoblotting, mass spectrometry and RNA analysis. The results indicate that masticatory myosin is expressed in some Sciuridae species but not in other closely related species with similar diets but having different nut-opening strategies. We also discovered that the myosin light chain 1 isoform associated with masticatory myosin heavy chain, in the same four Sciuridae species, is the embryonic/atrial isoform. We conclude that rodent speciation did not completely eliminate masticatory myosin and that its persistent expression in some rodent species might be related to not only diet but also to feeding style.
FOOTNOTES
This study was supported, in part, by grants IOB 0133613 and IOS 0749644 from the National Science Foundation. The valuable assistance of Alverna Hess Bugh, Kim Faler, and Terry Rastetter (Critter Control, Inc.), with sample collection, is greatly appreciated. The monoclonal antibodies used in this study (2F4, developed by Dr Joseph F. Y. Hoh,University of Sydney, and A4.951, developed by Dr Helen Blau, Stanford University) were obtained from the Developmental Studies Hybridoma Bank developed under the auspices of the NICHD and maintained by The University of Iowa, Department of Biology, Iowa City, IA 52242. The authors thank Dr Joseph B. Williams for very valuable comments on a previous version of this paper.
