Abstract: The purpose of this project is to provide research and career development training for Silvana Sidhom, a current PhD student at the University of Florida. This administrative supplement in response to PA- 21-071: ?Research Supplements to Promote Diversity in Health-Related Research (Admin Supp)? will facilitate career development for the candidate and as well as contribute to the mission of the parent project ? to define molecular targets downstream of the circadian clock that modulate muscle structure with implications for strength. The primary objectives of Ms. Sidhom?s proposed research will be to work on experiments related to Aim 2 of the parent grant. First, she will learn to use confocal imaging approaches with sarcomeric antibodies to define changes in the M-line and Z-line structural elements of the sarcomere from the control and muscle specific Bmal1 KO mice. Second, she will use AAV approaches to restore expression of selected sarcomeric genes, such as Tcap, to test if that is sufficient to restore structure and muscle force. Ms. Sidhom will work actively with Collin Douglas, another PhD student working on the parent grant as well as Dr. Christopher Wolff, a postdoctoral associate on this project. Dr. Esser, the PI of the R01, will be the primary mentor for Ms. Sidhom within the College of Medicine at the University of Florida. We have established her committee and this includes: Drs. Russ Hepple, Christiaan Leeuwenburgh and Richard Dunn. They are enthusiastic about Ms. Sidhom as a student and provide appropriate expertise in skeletal muscle and imaging approaches. Silvana has completed her first year of required courses so the committee will work with Ms. Sidhom to outlined a series of didactic courses, including the skeletal muscle course taught each fall. The committee will also help guide Silvana with experiential training activities that will equip her with the necessary skills to progress as an independent scientist and to fulfill the NIH mission to advance the careers of a diverse population of scientists. The project is directly related to Aim 2 of the parent grant: Specific Aim 2: To test the clock controlled genes, Rbm20 and/or Tcap, for their roles in sarcomere structure and muscle function. This aim will use AAV delivery of Tcap and/or Rbm20 in Bmal1 deficient muscle to test their contribution to sarcomere structure, myofibrillar protein composition and muscle function. Sarcomere structural elements will be obtained by super-resolution microscopy with deconvolution techniques with antibodies to define 2D and 3D properties including sarcomere length, thick filament centrality, M-band and Z line integrity. Deep RNA-sequencing will be performed on the Rbm20 muscles to define splicing changes. Functional outcomes will include ex vivo measures to test the impact of structural changes on both passive/stiffness and active/max force and rate of contraction properties.