INSCUTEABLE AND NUMB MEDIATE ASYMMETRIC MUSCLE PROGENITOR-CELL DIVISIONS DURING DROSOPHILA MYOGENESIS

Each larval hemisegment comprises similar to 30 uniquely specified som atic muscles. These derive from muscle founders that arise as distinct sibling pairs from the division of muscle progenitor cells. We have a nalyzed the progenitor cell divisions of three mesodermal lineages tha t generate muscle (and pericardial cell) founders. Our results show th at Inscuteable and Numb proteins are localized as cortical crescents o n opposite sides of dividing progenitor cells. Asymmetric segregation of Numb into one of the sibling myoblasts depends on inscuteable and i s essential for the specification of distinct sibling cell fates. Loss of numb or inscuteable results in opposite cell fate transformations- both prevent sibling myoblasts from adopting distinct identities, resu lting in duplicated or deleted mesodermal structures. Our results indi cate that the muscle progenitor cell divisions are intrinsically asymm etric; moreover, the involvement of both inscuteable and numb/N sugges ts that the specification of the distinct cell fates of sibling myobla sts requires intrinsic and extrinsic cues.