SEGREGATION OF MYOGENIC LINEAGES IN DROSOPHILA REQUIRES NUMB

Terminal divisions of myogenic lineages in the Drosophila embryo gener ate sibling myoblasts that found larval muscles or form precursors of adult muscles, Alternative fates adopted by sibling myoblasts are asso ciated with distinct patterns of gene expression, Genes expressed in t he progenitor cell are maintained in one sibling and repressed in the other. These differences depend on an asymmetric segregation of Numb b etween sibling cells, In numb mutants, muscle fates associated with re pression are duplicated and alternative muscles are lost. If numb is o verexpressed the reverse transformation occurs. Numb acts to block Not ch-mediated repression of genes expressed in muscle progenitor cells. Thus asymmetric cell divisions are essential determinants of muscle fa tes during myogenesis in Drosophila.