SPECIFIC MUSCLE IDENTITIES ARE REGULATED BY KRUPPEL DURING DROSOPHILAEMBRYOGENESIS

During Drosophila embryogenesis, mesodermal cells are recruited to for m a complex pattern of larval muscles. The formation of the pattern is initiated by the segregation of a special class of founder myoblasts. Single founders fuse with neighbouring nonfounder myoblasts to form t he precursors of individual muscles. Founders and the muscles that the y give rise to have specific patterns of gene expression and it has be en suggested that it is the expression of these founder cell genes tha t determines individual muscle attributes such as size, shape, inserti on sites and innervation. We find that the segmentation gene Kruppel i s expressed in a subset of founders and muscles, regulates specific pa tterns of gene expression in these cells and is required for the acqui sition of proper muscle identity. We show that gain and loss of Kruppe l expression in sibling founder cells is sufficient to switch these ce lls, and the muscles that they give rise to, between alternative cell fates.