Laminin A is required for follicle cell-oocyte signaling that leads to establishment of the anterior-posterior axis in Drosophila

The establishment of the anterior-posterior (AP) axis in Drosophila melanog aster requires signaling between the oocyte and surrounding somatic follicl e cells during oogenesis [1,2], First, a signal from the oocyte (Gurken (Gr k), a transforming growth factor-alpha (TGF alpha) homolog) is received by predetermined terminal follicle cells in which the epidermal growth factor receptor (EGFR) pathway is activated and a posterior fate is induced [2-4], Later, the posterior follicle cells send an unidentified signal back to th e oocyte, which leads to the reorganization of its cytoskeletal polarity, T his reorganization is required for proper localization of maternal determin ants, such as oskar (osk) and bicoid (bcd) mRNAs, that determine the AP pol arity of the oocyte and the subsequent embryo [2], We show here that when t he gene IanA, which encodes the extracellular matrix component laminin A, i s mutated in posterior follicle cells, localization of AP determinants is d isrupted in the underlying oocyte, Posterior follicle-cell differentiation and follicle cell apical-basal polarity are unaffected in the IanA mutant c ells, suggesting that laminin A is required for correct signaling from the posterior follicle cells that polarizes the oocyte, This is the first evide nce that the extracellular matrix is involved in the establishment of a maj or body axis.