2006 Abstracts - American Society of Animal Science

59 Interactions of a novel intermediate filament protein withtwo costameric proteins in muscle cells. N. Sun* and R. M. Robson,Iowa State University, Ames.The novel intermediate filament (IF) protein synemin and the major IFprotein desmin comprise the heteropolymeric intermediate filaments(IFs) that surround the myofibrillar Z-lines and link all adjacent myofibrilswithin striated muscle cells. In addition, the heteropolymeric IFslink Z-lines of the peripheral layer of cellular myofibrils to costamereslocated periodically along, and immediately subjacent to, the sarcolemma.In mammalian muscle cells, synemin is expressed as a larger Α-synemin splice variant, and a smaller Β splice variant. This differs fromavian muscle cells that express only one isoform, an ortholog of mammalianΑ-synemin. Avian synemin has previously been shown in our labto interact with vinculin. The detailed functions of the two syneminisoforms in mammalian muscle cells have remained unclear. The objectiveof this study was to determine whether one or both of the mammalianisoforms of synemin interacts with the costameric proteins vinculinand/or talin. Herein we report specific interactions of mammalian syneminwith both vinculin and talin. Coimmunoprecipitation assays show aninteraction of synemin with vinculin and talin in cultured rat smoothmuscle cells (A-10 cells). Solid-phase protein-protein binding studies(blot overlays) and in vitro GST pull-down assays demonstrate that aspecific region within mammalian Α-synemin interacts with both vinculinand talin. In addition, colocalization of Α-synemin with vinculin andtalin in focal adhesion sites, which contain proteins also present incostameres, was revealed by immunofluorescent staining of cultured A-10 cells. These results suggest that, via direct interaction with vinculinand talin, the larger Α-synemin isoform appears to function as a linkbetween the heteropolymeric IFs and the costameres located subjacentto the sarcolemma. The heteropolymeric IFs appear to help providemechanical integration of the cytoskeleton within mammalian musclecells. (Supported by USDA-CSREES-NRICGP Award 2003-35206-12823)Key Words: Myofibrils, Intermediate filaments60 The effect of Optaflexx ® dose and feeding duration ongrowth performance of steers. M. T. Van Koevering* 1 , A. L.Schroeder 1 , G. J. Vogel 1 , W. J. Platter 1 , A. A. Aguilar 1 , D. Mowrey 1 , S.B. Laudert 1 , G. E. Erickson 2 , R. Pritchard 3 , M. Gaylean 4 , and L. Berger 5 ,1 Elanco Animal Health, Greenfield, IN, 2 University of Nebraska, Lincoln,3 South Dakota State University, Brookings, 4 Texas Tech University,Lubbock, 5 University of Illinois, Urbana.Four studies using 1,867 steers were conducted to evaluate the effectsof Ractopamine HCL (RAC) on growth performance when fed for thefinal 28, 35 or 42 days (DUR) of the finishing period. At each study site,RAC was fed continuously to achieve intake doses of approximately 0(CON), 100 (LOW) and 200 (HIGH) mg/hd/d. Each study consisted offour to nine replicates for each RAC by DUR combination with 5 to 11steers/pen depending on study site. Analyses of growth performancedata were conducted using a linear mixed model procedure, Proc Mixed,SAS v8.2, with pen as the experimental unit. The statistical modelincluded RAC, DUR and RAC x DUR interaction as the independentfixed effects, and study and block within study as random effects. Therewere no RAC x DUR interactions (P>.62). Feed intake for steers fedeither level of RAC was not different compared to CON (P>.07). ADGwas greater (P