CHARACTERIZATION OF MYOSIN-IA AND MYOSIN-IB, 2 UNCONVENTIONAL MYOSINSASSOCIATED WITH THE DROSOPHILA BRUSH-BORDER CYTOSKELETON

The expression patterns of myosin-IA. (MIA) and myosin-IB (MIB), two n ovel unconventional myosins from Drosophila melanogaster, have been ch aracterized through immunoblot analysis and immunocytochemistry of emb ryos, larvae, and adults. The appearance and distribution of both prot eins during embryogenesis is correlated with the formation of a brush border within the alimentary canal as documented at the ultrastructura l level. MIA and MIB, both found predominantly at the basolateral doma in of immature enterocytes, exhibit increased expression at the apical domain of differentiated enterocytes co-incident with microvillus ass embly. Colocalization of MIA and MIB to larval and adult gut by confoc al microscopy demonstrates distinct but overlapping subcellular distri butions of these two proteins. In the larval brush border, MIA is enri ched in the subapical terminal web domain whereas MIB is found predomi nantly in the apical microvillar domain. In the adult gut, MIA and MIB both exhibit a microvillar component as MIA attains a more apical pos ition in addition to its previous terminal web locale. MIB is also fou nd in egg chambers at both the basolateral and apical surfaces of the somatic follicle cells during oogenesis, MIA and MIB both demonstrate ATP-dependent extraction from the larval brush border cytoskeleton and exogenous F-actin, biochemical properties characteristic of functiona l myosins-L. (C) 1995 Academic Press, Inc.