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First published online 10 January 2007
doi: 10.1242/dev.02786

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Dorsal-ventral midline signaling in the developing Drosophila eye

Department of Genetics and Development, College of Physicians and Surgeons, Columbia University, 701 West 168th St, HHSC 1120, New York, NY 10032, USA.

View larger version (74K): [in this window] [in a new window]   Fig. 1. Expression patterns, mutant phenotypes and genomic organization of slp. (A) Adult eye of the slp2 insertion line (slp2AVm) shows pigmentation in the anterior/ventral domain of the eye. (B) Genomic map of the slp locus showing the site of insertion of slp2AVm and the deletion induced (slpS37A, dotted lines). (C) slp-lacZ expression in the second-instar eye disc. (D) mirr-lacZ expression in the second instar. (E) Double staining of slp-lacZ (red) and Mirr (green) of second-instar eye disc. The two domains abut in the center of the disc. (F) Double staining of slp-lacZ (red) and Mirr (green) of third-instar head disc. The white arrowhead indicates the gap between the slp and Mirr expression domains. Arrows indicate slp expression in the dorsal regions of the extreme anterior of the eye disc, and in the posterior dorsal (relative to the eye) regions of the antennal disc. (G-I) Survival of slpS37A mutant clones (black) in third-instar eye discs, induced at different times of development. Yellow arrowhead indicates morphogenetic furrow (MF). (G) When clones are induced 0-24 hours AEL, twin spots (arrow) are readily evident in the ventral regions, but mutant clones are rarely observed. (H) Clones induced 24-48 hours AEL do not survive ventrally ahead of the MF (arrow points to a twin spot), but can be observed behind (white arrowheads), but are rounded with smooth borders. (I) Clones induced 48-72 hours AEL. slpS37A mutant clones (white arrowheads) survive ahead of the MF but show smooth borders. In all images, dorsal is up and posterior is left.

View larger version (56K): [in this window] [in a new window]   Fig. 2. The reciprocal effects of ectopic expression or loss of Slp and Iro. (A-A'') mirr-lacZ (red) is repressed by ectopic slp (green, arrow). Inset in A'' is higher magnification showing the autonomous repression of mirr-lacZ (arrows mark diminishing staining inside dorsal slp). (B-B'') slp-lacZ (red) is ectopically expressed in the inner regions of iro mutant clone (loss of green). Note that the ectopic slp-lacZ evident dorsal to the arrowed clone is an outgrowth of eye tissue into the head capsule. Why slp is non-autonomously induced in such outgrowths is unclear. (C-C'') slp-lacZ (red) is repressed by ectopic mirr (green, arrow). Inset in C'' shows the non-autonomous effects on slp-lacZ. Immediately surrounding the clone staining is absent, and surrounding this is a ring of cells showing decreased expression. (A''', B''', C''') Schematic summaries of the effects observed.

View larger version (126K): [in this window] [in a new window]   Fig. 3. (A,B) Double staining of fng in situ hybridization (red) and mirr-lacZ expression (green) in second (A) and mid-third (B) instars. Arrowhead in B indicates the interface between fng and mirr expression. (B') Arrows show the potential Fng+-Fng- interface in the ventral anterior regions of the eye disc as evidenced by fng expression. (C-E'') Regulation of fng expression by Slp and Iro as evidenced by fng in situ hybridization. (C) Clones ectopically expressing slp (green, arrows) show upregulation of fng transcription (red). (D) Clones ectopically expressing mirr (green, arrow) downregulate fng transcription (red). (E) When slp and mirr are co-expressed ventrally, fng transcription (red) is repressed in ventral (arrowhead), but not upregulated in dorsal (arrow) regions.

View larger version (46K): [in this window] [in a new window]   Fig. 4. N activation downregulates slp expression.(A-A'') Clones of Nintra (green, arrows) show downregulation of slp-lacZ expression (red). (B,C) The effects of a 24-hour temperature shift on Nts/+ control discs (B) and Nts/Y experimental discs (C) stained for slp-lacZ (green) and Mirr (red). In the control, the gap (arrowhead) forms normally, but in the Nts/Y, slp transcription is unaffected and the gap fails to form.

View larger version (75K): [in this window] [in a new window]   Fig. 5. N activity and expression of its ligands in second and third-instar eye discs. (A-A'') In late-second-instar eye discs, Ser (arrow, green) is expressed in a broad swath about the D-V midline, whereas Dl (red) expression is more general. (B) Mid-third-instar N activation evidenced by N-GV/UAS-lacZ staining. Ahead of the wave front, strong N activity is in a line running from the D-V midline and curving up into the anterior dorsal region (arrow), and weak N activity is detected in the ventral part (arrowhead). (C) Ser (arrows and arrowheads, green) is expressed in a domain corresponding to the lines of both strong and weak N activation but occupying broader areas. (C') Dl (arrows, red) is upregulated in a line corresponding to the profile of strong N activation, and DI expression can also be seen weakly in a position corresponding to the weaker N activation (arrowhead). (D) Late-third-instar N activity (blue) is detected in the region of the D-V midline and head capsule on both the dorsal (arrow) and ventral (arrowhead) side. (D') Ser (green) is expressed in a broader region corresponding to N activity. (D'') Dl (red) is mainly expressed behind the MF, but is also expressed at the anterior extreme in both dorsal (arrow) and ventral (arrowhead) regions.

View larger version (96K): [in this window] [in a new window]   Fig. 6. (A-A'') High levels of Ser expression (green) correspond with the loss of slp-lacZ (red) in third-instar eye discs. eyg-Gal4/UAS-GFP expression (blue) demarcates the eye field (dotted line indicates the anterior extreme of the eye); Ser expression anterior to this relates to patterning of head capsule tissues. Arrow in A' indicates the downregulation of slp expression in the ventral spur corresponding with high Ser expression. (B-B'') Ser (green) is expressed in cells not expressing mirr-lacZ (red), except in the most anterior regions (arrow in B''). (C-D'') The roles of N, Slp and Iro in regulating Ser upregulation in third-instar discs. (C) Ectopic expression of slp (red, arrow) in the region of the gap shows a downregulation of Ser expression (green). Note that slp does not repress Ser completely. (D) Ectopic expression of mirr in the region of the gap (red, arrow) shows a downregulation of Ser expression (green). Note that the non-autonomous induction of Ser (arrowhead) is likely to be caused by the new Fng+-Fng- interface induced in the ventral cells.

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