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Fig. 9. Integrative model of Yan regulation and function during border cell
migration. (A) The JAK/STAT and Notch pathways specify the group of anterior
terminal cells (a-TC) around the pair of polar cells (PC, green). Cells that
are directly adjacent to the anterior polar cells are specified as BCs
expressing Slbo. With the exception of the polar cells, Yan (blue) is
expressed in all a-TCs, and becomes upregulated immediately prior to their
transit from a static, epithelial state to a migratory state (dark blue).
Posterior terminal cells (red) are specified by Gurken (EGF) signaling. Pvf1
(orange), secreted from the oocyte, guides BCs towards the oocyte. As BCs face
increasing Pvf1 levels from anterior to posterior, Yan expression levels
decrease (light blue circles). (B) Regulatory relationships between signal
transduction pathways that control BC migration. JAK/STAT and Notch signaling
pathways regulate the expression of slbo and yan, whereas
PVR and EGFR induction lead to Yan phosphorylation and its inactivation. The
transient upregulation of Yan at the initiation of BC migration facilitates
DE-Cad turnover at the plasma membrane to enable BCs to make and break
adhesive contacts, and to promote detachment from the epithelium and cell
movement. Coordinated, dynamic changes in cell adhesion and cytoskeletal
organization enable BCs to migrate in a stereotypic fashion.
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