Identification of transcription factors and chromatin regulators with novel roles in muscle morphogenesis. Krista C. Dobi¹, Marc S. Halfon², Mary K. Baylies¹. 1) Dept Dev Biol, Sloan-Kettering Inst, New York, NY; 2) Biochem Dept, SUNY Buffalo, Buffalo, NY.

   Skeletal muscles come in a variety of shapes and sizes, from the rounded muscles that control eye blinking to the elongated muscles of your legs that allow you to run. These muscles have different functions, and they also have different susceptibilities to diseases such as muscular dystrophy. Potential myoblast transfer and stem cell therapies to repair muscle wasting due to aging or disease will require the ability to generate muscles with specific morphologies. The 30 body wall muscles in each hemisegment of the Drosophila embryo are distinguishable by properties such as size, shape, attachment and gene expression. To identify new regulators of Drosophila embryonic muscle morphogenesis, we isolated muscle subsets using FACS, purified RNA from these cells and analyzed their transcriptional profiles by microarray. We identified ~600 differentially regulated genes, representing diverse functions like gene expression and cytoskeletal organization. GO analysis revealed that a significant number of up-regulated genes encode transcription factors and chromatin regulators. We confirmed mesodermal expression of these genes by in situ hybridization and tested whether loss of these factors disrupted the muscle pattern. We characterized 12 genes with novel functions in the Drosophila embryonic somatic muscle: zinc finger proteins CG8145, Lola, Alhambra and Charlatan; bHLH protein Cropped; T-box family member Midline; elongation factor Elongin-B; Mediator complex member Med13/Skuld; and chromatin regulators Little imaginal discs (Lid), Lysine-specific demethylase 2 (Kdm2), Grunge (Gug) and Sin3A. Our studies revealed new roles for highly conserved general transcription factors (Med13, Elongin-B) and chromatin regulators (Sin3A, Gug, Lid and Kdm2) in the regulation of muscle morphogenesis. Current experiments are providing us with a clearer picture of how regulation of transcription and chromatin structure is crucial for muscles to achieve distinct sizes and shapes.