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 melanogaster requires signaling between the oocyte and surrounding somatic follicle cells during oogenesis [1] [2]. First, a signal from the oocyte (Gurken (Grk), a transforming growth factor-alpha (TGFalpha) 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] [3] [4]. Later, the posterior follicle cells send an unidentified signal back to the oocyte, which leads to the reorganization of its cytoskeletal polarity. This reorganization is required for proper localization of maternal determinants, such as oskar (osk) and bicoid (bcd) mRNAs, that determine the AP polarity of the oocyte and the subsequent embryo [2]. We show here that when the gene lanA, which encodes the extracellular matrix component laminin A, is mutated in posterior follicle cells, localization of AP determinants is disrupted in the underlying oocyte. Posterior follicle-cell differentiation and follicle cell apical-basal polarity are unaffected in the lanA mutant cells, suggesting that laminin A is required for correct signaling from the posterior follicle cells that polarizes the oocyte. This is the first evidence that the extracellular matrix is involved in the establishment of a major body axis.