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fringe and Notch specify polar cell fate during Drosophila oogenesis

Muriel Grammont and Kenneth D. Irvine

Howard Hughes Medical Institute, Waksman Institute and Department of Molecular Biology and Biochemistry, Rutgers The State University of New Jersey, Piscataway, NJ 08854, USA



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  		Fig. 1. Schematic of wild-type ovariole. The arrangement and fates of different cells in the germarium and in stage 2 (S2) and stage 9 (S9) follicles are indicated: oocyte nucleus (brown) other germline cell nuclei (gray), main-body follicle cell nuclei (black), polar cell nuclei (red) and stalk cell nuclei (green). The border cells include the anterior polar cells and several main-body follicle cells, and migrate between the nurse cells at stage 9. Roman numerals indicate different regions of the germarium. In all figures, anterior is towards the left.

 


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  		Fig. 2. Oogenesis defects in fng hypomorphs. (A-H) Follicles with nuclei stained (Hoechst) and oocytes (asterisks) and interfollicular stalks (arrows) are indicated. (I,J) Follicles stained with Phalloidin (red) and Hoechst (blue). (A,B) wild type. (C) fng52/fngM69 follicle with two 16-cell cysts. (D) fng52 follicle with six nurse cells. (E) fng2/fng80 stalk with nine cells. (F) fng52 stalk with a cluster of cells. (G) fng2/fngM69 double stalk. (H) fng52 ovariole with an abnormal epithelium at the posterior of stage 5 and stage 9 follicles (arrowheads). (I) Posterior of a wild type stage 7 follicle with follicular cells in a monolayer. (J,J') Posterior of a fng52 stage 7 follicle with follicular cells that do not form a monolayered epithelium (large arrow). Nuclei of two adjacent cells (small arrows) and a round cell that does not contact the germline (arrowhead) are indicated.

 


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  		Fig. 3. fng expression. (A-D,F,J,K) fng expression shown by in situ hybridization. (E,G,I) X-gal staining in fng-lacZRF584. (H) Serrate expression shown by antibody staining. Arrows point to polar cells. (A,B,E) Germaria, with different regions, as defined by morphological criteria (King, 1970; Spradling, 1993) indicated by roman numerals. Arrowhead in B points to the IIb-III border. (C,D) Stage 3 (C) and stage 5 (D) follicles with fng expression restricted to polar cells. (E) Germarium, followed by stage 2 and 3 follicles. (F) Stage 7 and 8 follicles with fng expression in posterior cells that contact the oocyte. (G) Polar and stalk cells between stage 2 and 3 follicles express fng. (H) Serrate is expressed in all somatic cells during follicle formation. (I) Stage 7 follicle with fng expression in anterior and posterior polar cells. Expression in other posterior cells is present (bracket). No expression is detectable in germline cells. (J) Stages 7 and 9 follicles. At stage 9, fng is expressed in follicle cells that migrate towards the oocyte (bracket). Among the border cells, fng is expressed only in polar cells (arrow). (K) Stage 10b follicle; antero-dorsal follicle cells do not express fng (asterisk).

 


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  		Fig. 4. Compound and stalkless follicles in fng13 clones. fng13 (A,C-F) and wild-type control (B) clones marked with arm-lacZ (A) or {pi}-Myc (B-F). Left panels show nuclei (white), while right panels show clone markers (green). In the right-hand column, figures show separate images of the same follicle. Arrows indicate polar cells, arrowheads point to the absence of interfollicular stalks. In E’, Fas III staining is also shown (red). (A) fng13 clones in the germline, asterisks mark mutant cysts. (B) In wild type, a follicle with an entirely {pi}-Myc- epithelium can form. (C-F) fng13 clones in the soma. (C,D) Compound follicles with fng+ cells at both extremities. In D, only the polar cells are fng+ at the anterior. (E) Stalkless follicles separated by a fused bilayered epithelium. Two posterior polar cells (inset) are present in the epithelium of the younger follicle. (F) Stalkless follicles separated by a monolayer epithelium. The epithelium of the younger follicle is discontinuous (bracket).

 


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  		Fig. 5. fng is required to specify polar cells. fng13 clones marked with {pi}-Myc (green) and stained for nuclei (white) and Fas III (red). Arrows indicate polar cells; arrowheads point to the absence of polar cells. (A) Stage 2 follicle with fng+ main-body follicular cells and fng- stalk cells, A" is a Nomarski image. Brackets indicate abnormal stalks. (B) Stage 6 follicle with fng- cells at the anterior and no anterior Fas III-positive cells. The more anterior follicle (partially visible) has only two fng+ cells at its posterior (staining intensity enhanced in inset); they are polar cells and the follicle appears normal. (C) Stage 7 follicle with fng- main-body follicle cells and fng+ polar cells. The image is a composite from two different focal planes of the same follicle, fused at the broken line.

 


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  		Fig. 6. Requirements for fng and Notch in stalk cells. (A-C) fng13 or (D) N55e11 clones marked with {pi}-Myc (green) and stained for nuclei (white or blue) and P3F or FasIII (B,C, red). (A) Stalk with eight fng- cells and 1 fng+ cell (white dot). Although FasIII staining is never detected in fng- cells in the follicular epithelium, it persists in fng- cells in the stalk. Arrow points to polar cells. (B) Stalk with 11 cells, four are fng+. All express 93F (arrowhead). Arrow indicates a gap into the follicle epithelium, presumably due to the absence of polar cells. The adjacent stalk cell is fng+ (arrowhead). (C) Stalkless follicles with four 93F-expressing cells (arrowhead). (D) Stalk with >15 cells that is mosaic for Notch.

 


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  		Fig. 7. Ectopic activation of Notch can induce extra polar cells. Arrows indicate polar cells. (A-C) Flip-out clones expressing fng marked with GFP (green) and stained for expression of A101 (ß-galactosidase, red). (A) Stage 4 follicle with three polar cells. (B) Stage 8 follicle with ectopic fng expression including the posterior polar cells, only two polar cells form. Inset shows A101 expression for the boxed region. (C) Stage 10A follicle with ectopic fng expression in follicle cells adjacent to the posterior polar cells, only two polar cells form. (D) X-gal stain of stage 3 wild-type follicle with E(spl)mß-lacZ expressed specifically in the polar cells. (E) Stage 5 follicle with Flip-out clones expressing activated Notch, marked with GFP and stained for Fas III (red). Three polar cells form (arrow). Lateral follicular cells also express activated-Notch, but are not transformed into polar cells.

 


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  		Fig. 8 Notch is required to specify polar cells. (A-D) N55e11 clones marked with {pi}-Myc (green), and stained for nuclei (white) and Fas III (A,C), A101 (B) or E-Cadherin (D) (red). In all panels, arrows indicate polar cells and arrowheads point to Notch- clones. (A) Stage 8 follicle. Notch- cells express Fas III. (B) Stage 5 follicle. No A101 expression is detected in Notch- cells within the follicular epithelium. (C) Stage 5 follicle. No Fas III expression is detected in the Notch- cells within the follicular epithelium. The arrowhead points to the absence of Fas III-expressing polar cells. (D) Stage 3 follicle with only ten Notch+ cells at the anterior and three Notch+ cells at the posterior. The follicle appears normal and includes polar cells.

 

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