The role of the Drosophila follicular epithelium in the assembly of an egg.

摘要

The follicle cell monolayer that encircles each developing Drosophila oocyte contributes actively to egg development and patterning, and also represents a model stem cell-derived epithelium. We identified mutations in the receptor-like transmembrane tyrosine phosphatase Lar that disorganize follicle formation, block egg chamber elongation and disrupt Oskar localization, an indicator of oocyte anterior-posterior polarity. Alterations in actin filament organization correlate with these defects. Actin filaments in the basal follicle cell domain normally become polarized during stage 6 around the anterior-posterior axis defined by the polar cells, but Lar mutations frequently disrupt polar cell differentiation and actin polarization. Lar function is only needed in somatic cells, and for Oskar localization its action is autonomous to posterior follicle cells. Polarity signals may be laid down by these cells within the extracellular matrix (ECM), possibly in the distribution of the candidate Lar-ligand Laminin A, and read out at the time Oskar is localized in a Lar-dependent manner. Lar was not required autonomously to polarize somatic cell actin during stages 6. We showed that Lar acts somatically early in oogenesis during follicle formation, and postulate that it functions in cells that are required for polar cell specification and differentiation. Our studies suggest that positional information can be stored transiently in the ECM. A major function of Lar may be the transduction of such signals.; The ECM can modulate expression and activation of receptors required for maintenance of stem cells, such as Integrins. Our analyses of the germarium ECM shows a local variation in the region where the somatic stem cells housed.