Localisation of the specific <i>corpora allata</i> and prothoracic <i>snail cis</i> regulatory elements.

(A) Scheme of a st16 embryo representing the CA and PG in green, the corpora cardiaca (CC) in red and the aorta and heart in blue. The migratory route followed by the three gland primordia towards their final position in the ring gland is represented by arrows starting from their approximate location at st11. (B) sna locus indicating the position of the transcription unit (black), the two mesoderm enhancers (brown), the ring gland enhancer (blue) and the snaΔrgR2 deletion. (C-F) sna RNA expression in wild type embryos at st11 (C) and st13 (D), or snaΔrgR2 embryos at st11 (E) and st13 (F). Arrows point to the CA and PG primordia, asterisks mark the absence of sna transcription. (G-H) sna-rg-GFP reporter in a st11 wild type embryo (G) before CA and PG coalescence, and at st13 (H) showing the coalesced CA/PG migrating towards the dorsal midline. (I-J) sna-rg-GFP snaΔrgR2 homozygous embryos showing the CA and PG primordia at st11 (I) and at st13 (J) when degeneration is noticeable (asterisks). (G’-J’) Show DCP-1 co-expression (white) in the same embryos to reveal apoptosis. In control embryos (G’-H’) DCP-1 activation is restricted to ectodermal cells. In sna-rg-GFP snaΔrgR2 homozygous embryos, gland cells show high levels of DCP-1 at st13 (J’) (yellow arrows). At st11 (I’), just after gland specification, DCP-1 starts being detectable before overt gland degeneration. (K-M) snaΔrgR2 homozygous embryos carrying the sna-rg-mCherry reporter (green) and a sna-BAC rescue construct. The Sna protein in the BAC is tagged with GFP (red) revealing its expression in the gland primordia before coalescence (K, yellow because overlap with sna-rg expression), after coalescence (L, arrow), and after integrating in the ring gland (M). Apart from the gland primordia, the Snail BAC protein reveals other sites of expression: the oenocytes and the wing and haltere primordia (M, asterisks). Note that cell viability and migratory behaviour of the CA and PG are fully rescued by the BAC. All figures show lateral views with anterior left and dorsal up.