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A dual function of phyllopod in Drosophila external sensory organ development: cell fate specification of sensory organ precursor and its progeny

Haiwei Pi, Hui-Ju Wu and Cheng-Ting Chien*

Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan 11529



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  		Fig. 1. Two classes of bristle phenotypes in phyl mutant adults. (A,C,E,G,I) Wild types. (B,D) phyl1/phyl4 and (F,H,J) phyl2245/phyl4 mutants. (A,B) Adult nota. (C,D) Adult abdominal segment 2-4. Arrows in B and D mark the abnormal bristles. (E-J) X-gal staining of nota dissected from ac-lacZ (E,F), A101 (G,H), and ase-lacZ (I,J) pupae at 14-18 hour APF (for ac-lacZ and A101) or 18-22 hour APF (for ase-lacZ).

 


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  		Fig. 2. Transformation from neurons and sheath cells to outer support cells in embryos lacking phyl. In this and all the following figures, neurons are stained with anti-Elav antibody (red), sheath cells are stained with anti-Prospero antibody (green), and cells of es organs are stained with anti-Cut antibody (purple). (A,B) Abdominal hemisegments of the PNS in wild type (A), and phyl1/phyl2 (B) embryos. L, lateral region and V, ventral region of the PNS. (C) In the A1(2)29 embryo, the dm region of each abdominal hemisegment contains four outer support cells (blue), two neurons (red), and two sheath cells (green). In total, there are eight Cut-positive cells for these two es organs (E). (D) In phyl2245 /phyl2245 embryos, six outer support cells with one neuron and one sheath cell (left), or eight outer support cells (right) were most frequently observed. (F) In most cases, eight Cut-positive cells are still present (left hemisegment) in phyl2245/phyl2245. Occasionally, four Cut-positive cells were observed (right). Schematic drawings of the two dm es organs are on the left.

 


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  		Fig. 3. Misexpression phenotypes of phyl. (A,B) Expression pattern of UAS-GFP/+; Eq-GAL4/+. (A) The wing disk at 3 hour APF. Anterior is to the left. (B) The developing notum at 7 hour APF. At this stage, the notal regions of the two wing disks are attaching to each other to form a complete notum. The arrows indicate the future midline region and anterior is to the top. (C) Wild type notum, and (E) its midline region. (D,F) In the UAS-phyl/+; Eq-GAL4/+ notum, the density of microchaetes increases (D), and is highest in the midline region (F). (G) Wild-type and (H) UAS-phyl/+; dpp-GAL4/+ adult scutella. (I,J) X-gal staining of A101 in wild-type (I) and UAS-phyl/+; dpp-GAL4/+ (J) pupal scutella. Ectopic SOP cells are indicated by arrows in (J). (K,L) Confocal images of the abdominal hemisegments in embryos stained with anti-Elav antibody. (K) Wild-type and (L) sca-GAL4/UAS-phyl. (M,N) Confocal images of the abdominal dm region of a sca-GAL4/ UAS-phyl embryo to reveal the numbers of neurons (red) and sheath cells (green) (M), and the total numbers of es organ progeny (N). (O,Q) In GAL4109-68/UAS-phyl adults, the hair cells and socket cells of the microchaetes are missing (O), and are transformed into neurons (red) and sheath cells (green) (Q). (P) Clusters of one neuron and one sheath cell were seen in wild-type pupal notum.

 


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  		Fig. 4. phyl, sina and ttk interact genetically in es organ development. (A-F) Adult nota. (G-L) Adult abdominal segment 2-4. The genotypes of A-L are indicated above. (M,N) X-gal staining to show expression of A101 (M) and ase-lacZ (N) in sina2/sina3 pupal nota. In M, the dashed line marks the midline, and arrows mark the region where A101-positive cells were missing. (O,P) sina mutant embryos that lack both maternal and zygotic sina transcripts show strong reduction in the number of neurons (red) and sheath cells (green) (O), but most of the dm region still contains eight Cut-positive cells (purple) (P). (Q) Anti-Elav staining of a phyl1/phyl2; ttkosn/+ embryo. The ventral region was out of focus.

 


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  		Fig. 5. phyl acts upstream of ttk and downstream of N. (A,B) Adult nota of Eq-GAL4/UAS-ttk69 (A) and UAS-phyl/+; Eq-GAL4/UAS-ttk69 (B). (C) A101 expression in Eq-GAL4/UAS-ttk69 pupal notum. Most of A101-positive cells were missing. (D) Adult notum with a phyl2 mutant clone (clone boundary is indicated by black lines). (E) Notum of Nts flies. (F) Adult notum of Nts with a phyl2 mutant clone (clone boundary is marked with black lines). Most bristles in the mutant clone were missing. (G-L) Anti-Elav staining of the embryonic abdominal hemisegments. (G) Wild type, (H) ttkosn/ttkosn mutant, (I) phyl1/phyl2; ttkosn/ttkosn double mutant. Neuron overproduction was observed in both mutant embryos (H,I). (J) Nts; phyl1/phyl2 double mutant at 17°C. (K) Nts mutant at 32°C. (L) Nts; phyl1/phyl2 double mutant at 32°C.

 


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  		Fig. 6. phyl expression is negatively regulated by N signaling. Whole-mount in situ hybridization of phyl mRNA in wing disks (A-D) and embryos (E-L). (A) phyl expression in wild-type wing disk. (B,C) Higher magnification of the phyl expression in SOP cells of wing margin (B) and macrochaetes (C). (D) phyl expression in Nts mutant wing disk. (E-G) Late third instar larvae of Nts were incubated at 30°C for 5 hours before dissecting. In the embryos, phyl mRNA is expressed in (E) neuroblasts at stage 9 (ventral view), (F) SOP cells at stage 11 (lateral view), and (G) a subset of PNS cells at stage 13 (lateral view). (H) phyl mRNA in PNS is no longer detected in the numb1 mutant, and (I) is reduced in the sca-GAL4/+;UAS-NACT/+ embryo. (J) In wild-type embryos, phyl is expressed in approximately 20-30 SOP cells in each hemisegment at stage 11. (K,L) phyl is expressed in many more cells in the N55e11 (K) and E(spl)b32.2 gro+ (L) mutant embryos at stage 11. (M,N) Confocal images of the embryonic abdominal hemisegments stained with anti-Elav antibody (red) and anti-prospero antibody (green). (M) sca-GAL4/+; UAS-NACT/+ embryo. (N) sca-GAL4/+; UAS-NACT UAS-phyl embryo.

 


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  		Fig. 7. Summary and models of phyl in es organ development. (A) The process of es organ development. (B) In phyl mutants, SOP fails to form although the expression of proneural genes is not affected. Also, phyl is required for cell fate specification of IIb cells; IIb cells are transformed to IIa cells in phyl mutants (C). (D,E) Our data suggests that Phyl is expressed in SOP and IIb cells, and functions together with Sina to degrade Ttk. In non-SOP cells (which ultimately become epidermal cells) and IIa cells, the levels of phyl mRNA are down-regulated by N signaling.

 

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