Fig. 7. (A-J) GmASH prefigures the regions where invagination sites arise. Confocal micrographs (A-E) and light micrographs of (F-J) of the first leg hemisegment. Anterior is towards the top, the midline is towards the left. (A,F) GmASH is expressed at heterogeneous levels in the central region of the hemisegment before formation of the invagination sites at stage 1 (arrowheads). (B,G) The first invagination sites (arrowheads in B) arise in the expression domains of GmASH at stage 2. At this time the gene is expressed in distinct regions of the hemisegment (arrowheads in G). In addition, GmASH shows transient expression in the invaginating cells. (C,H) At stage 3, the second wave generates invagination sites in the regions prefigured by GmASH (arrowheads in C, compare to G). At this time, the expression domains of GmASH form a semicircle around the central region where an invagination site have already formed (arrowheads in H). (D,I) Again invagination sites arise in the expression domains of GmASH (arrowheads). At this time the gene is re-expressed in distinct regions (arrowheads in I). (E,J). In these regions the last invagination sites arise during the fourth wave of neural precursor formation at late stage 4. GmASH expression is transiently maintained in the invaginating cell groups (arrowhead in J). Scale bar: 50 µm in A-J.