BETA(HEAVY)-SPECTRIN HAS A RESTRICTED TISSUE AND SUBCELLULAR-DISTRIBUTION DURING DROSOPHILA EMBRYOGENESIS

The components of the membrane skeleton play an important role in main taining membrane structure during the dynamic changes in cell shape th at characterize development. beta(Heavy)-spectrin is a unique beta-spe ctrin from Drosophila melanogaster that is closer in size (M(r)=430x10 (3)) to dystrophin than to other beta-spectrin members of the spectrin /alpha-actinin/dystrophin gene super-family. Here we establish that bo th the subcellular localization of the beta(Heavy)-spectrin protein an d the tissue distribution of beta(Heavy)-spectrin transcript accumulat ion change dramatically during embryonic development. Maternally loade d protein is uniformly distributed around the plasma membrane of the e gg. During cellularization it is associated with the invaginating furr ow canals and in a region of the lateral membranes at the apices of th e forming cells (apicolateral). During gastrulation the apicolateral s taining remains and is joined by a new apical cap, or plate, of beta(H eavy)-spectrin in areas where morphogenetic movements occur. These loc ations include the ventral and cephalic furrows and the posterior midg ut invagination. Thus, dynamic rearrangement of the subcellular distri bution of the protein is precisely coordinated with changes in cell sh ape. Zygotic message and protein accumulate after the germ band is ful ly extended, in the musculature, epidermis, hindgut, and trachea of th e developing embryo. beta(Heavy)-spectrin in the epidermis, hindgut, a nd trachea is apically localized, while the protein in the somatic and visceral musculature is not obviously polarized. The distribution of beta(Heavy)-spectrin suggests roles in establishing an apicolateral me mbrane domain that is known to be rich in intercellular junctions and in establishing a unique membrane domain associated with contractile p rocesses.