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The functions of pannier during Drosophila embryogenesis

Centro de Biología Molecular, Universidad Autónoma de Madrid, 28049 Madrid, Spain

View larger version (77K): [in a new window]   Fig. 1. Expression of pnr during embryonic development. (A,B) Lateral view (anterior left, dorsal up) of early embryos (stages 5-6) showing the distribution of pnr transcripts, and Eve (A) and Ftz (B) proteins. pnr expression covers a broad dorsal domain. The anterior limit is close to the second eve stripe, although there is some low level expression anterior to the eve stripe, which is not visible in the picture. The posterior limit coincides well with the anterior border of the seventh Ftz stripe. (C) Dorsal view of a late embryo (stage 13) doubly labelled for pnr mRNA and Cad protein. pnr transcripts lack in the amnioserosa region (am) and in the A8 segment. There is pnr expression in A9, but not in A10, where cad is expressed. (D,E) Confocal images of lateral view of en-lacZ embryos doubly stained with anti-Pnr antibody and anti ß-gal. The spotty appearance of Pnr label indicates the protein is in the cell nucleus. There is Pnr protein in the A8 segment in stage 10 (D), but not in stage 11 (E). (F) Lateral view of a stage 12 embryo showing pnr and dpp expression. The dorsal dpp stripe is within the Pnr domain and shares the same dorsal limit at the junction with the amnioserosa.

View larger version (79K): [in a new window]   Fig. 2. (A,B) Distribution of pnr RNA in mutant embryos for Abd-BM1 and linG1. There is pnr expression in A8, in contrast to wild-type embryos (compare with Fig. 1C). (C) Confocal images of a double labelling for pnr and brk expression in several segments of an stage 13 embryo. Dorsal is towards the top. Although brk (red) is expressed ventral to pnr (green) there is a zone of overlap, as indicated by comparing the images of the A1 and the A2 segments, for which only the green (A1) and red (A2) channels are shown.

View larger version (74K): [in a new window]   Fig. 3. Larval phenotype of pnrVX6 larvae. The two dark-field photographs on the left show a lateral view of a wild-type and a pnrVX6 first instar larva and the phase contrast photographs on the right compare epidermal pattern elements of the two genotypes. The pnrVX6 exhibits the characteristic basket shape, and the dorsal closure is defective (not visible in the photo). From a side view it is possible to recognise three different pattern elements arrange along the DV axis of the wild-type. In the most dorsal position (top) there are dorsal triangles (dt, arrows) and spinules (sp), but in the dorsolateral region there are only spinules. In the ventral side of the larva (bottom), the principal elements are the denticles (de). Spinules and dorsal triangles are lacking in this region. In pnrVX6 larvae, the dorsal triangles are missing but spinules form and appear to be expanded towards the dorsal region.

View larger version (125K): [in a new window]   Fig. 4. Developmental consequences of ectopic pnr activity. (A) Ventral view of a wild-type first instar larva showing the characteristic denticle belts that differentiate in the ventral side. (B) Ventral view of a first instar larva of genotype Ubx-Gal4/UAS-pnr showing transformation of the ventral region into dorsal one. Note that the ventral denticles of most of the abdomen are replaced by dorsal spinules which are thinner. (C) Embryo of the same genotype as in B stained with anti-Pnr antibody to show that the Pnr protein is present in the Ubx domain. The area stained covers the sum of the normal domains of pnr and Ubx. The arrow marks the anterior limit of the Ubx domain (T2p); from this point the Pnr protein is present in high levels down to abdominal segment 6. Note pnr expression in the amnioserosa cells. (D,E) Phase contrast pictures of the thoracic region of a wild-type and a Ubx-Gal4/UAS-pnr larva. In the anterior region of the T2 segment there is no difference between them; they differentiate typical ventral thoracic pattern elements such as Keilin’s organs (ko), ventral pits (vp) and denticles (de). In the posterior T2 segment, the Ubx-Gal4/UAS-pnr larva exhibits some spinules (sp), characteristic dorsal elements, but the differences are clearer in T3 where all ventral elements lack and are replaced by spinules. (F,G) Ventral view of an arm-Gal4/UAS-pnr larva showing a virtually complete transformation of ventral into dorsal structures. Three abdominal segments are magnified in G to show (arrows) the presence of dorsal triangles around the circumference of the larva, thus suggesting the transformation is towards dorsomedial pattern. (H) Ventral view of abdominal segments of a larva of genotype wg-Gal4/UAS-pnr. As wg is expressed in the region normally differentiating naked cuticle, the denticle (de) belts are not affected, but part of the naked region is transformed into the corresponding dorsal one and differentiates dorsal spinules (sp).

View larger version (82K): [in a new window]   Fig. 5. pnr acts as a positive regulator of ush and dpp in late embryonic development. (A) Wild-type stage 13 embryo showing ush expression. It covers the amnioserosa and an epidermal region where it is coincident with pnr. (B) ush expression in pnrVX6 embryo. The epidermal expression has disappeared but it remains in the amnioserosa. (C) ush expression in an en-Gal4/UAS-pnr embryos showing ectopic ush activity in the posterior compartments. (D) Wild-type expression of dpp in an stage 11 embryo. There are two parallel stripes of dpp expression extending from the head to the end of the abdomen; the dorsal one abuts the amnioserosa (am). (E) dpp expression in a pnrVX6 embryo showing the lack of the dorsal dpp stripe close to the amnioserosa, whereas the lateral one is not affected. (F) en-Gal4/UAS-pnr stage 13 embryo showing ectopic dpp activity in the posterior compartments dorsal and ventral to the lateral dpp stripe. The dorsal stripe is not visible in the picture.

View larger version (91K): [in a new window]   Fig. 6. Loss of activity of Pnr does not affect puc expression. The top picture is a lateral view of a wild-type late embryos doubly stained for pnr (green) and puc (red). The latter is expressed in a line of cells at the dorsal edge of the Pnr domain. The bottom picture is a dorsal view of a pnrVX6 mutant embryo showing normal Puc activity.

View larger version (36K): [in a new window]   Fig. 7. Lack of effect on the Pnr protein in the amnioserosa. The LP1 line drives expression only in the amnioserosa, as indicated by the LP1/UAS-lacZ embryo shown on the top. (A) Confocal image of a doubly labelled embryo stained for pnr and Kruppel. (B,C) The green and red channels, indicate that although there are high levels of pnr in the amnioserosa (B) there is no effect on Kr expression (C). (D) Embryo of the same genotype doubly stained for pnr and dpp. The expansion of pnr expression to the amnioserosa does not modify dpp expression, which remains normal.