Fig. 7.

A model: Pax6-dependent expression of Shroom3 in the lens pit induces apical constriction and facilitates placodal invagination. A model illustrating Shroom3 activity is an important component of the morphogenesis mechanisms required for invagination of the lens pit. (A) The activity of Shroom3 becomes important at ~E9.5, just prior to lens pit invagination. (B) At this time, inductive signaling that involves Fgf receptor signaling via the Frs2α adapter (blue), Bmp7 signaling (orange) and the Meis transcription factors (gray), results in the transcriptional upregulation of Pax6 via the EE and SIMO control elements. In turn, Pax6 is required, directly or indirectly, for the expression of Shroom3 and engagement of the machinery that results in apical constriction in lens pit epithelial cells. (C) It is likely that Shroom3-induced apical constriction is one of several mechanisms of morphogenesis that combine to achieve placodal invagination and the formation of a lens pit at E10.5.