Fig. 2. Expression patterns of Fgf10 (A-I,M) and Fgfr2b (J-L,M) in the developing eyelid. (A) Fgf10 is expressed in the underlying mesenchyme of the prospective eyelid region (arrowheads). (B) Higher magnification of the lower eyelid region in A. (C) Fgf10 is expressed in the mesenchyme of the developing whiskers (arrowheads), which is shown as an internal control for in situ hybridization. (D) Fgf10 is expressed in the mesenchyme underneath the upper (u) and lower (l) eyelid protrusions. The arrowhead indicates Fgf10 expression in the future corneal stroma. (E,F) Higher magnification of the eyelid protrusion in D. Fgf10 is expressed in the surrounding mesenchyme at the bottom of the eyelid groove (arrow in F) in addition to the eyelid tip. (G) Whole-mount in situ hybridization of the eye region. Fgf10 is expressed in the eyelid region and hair follicles. The Fgf10 expression is more intense in the lower eyelid. The inner canthus (towards the nose) is to the right; the outer canthus (towards the temples) is to the left. (H,I) Section in situ hybridization, showing more intense Fgf10 expression (arrowheads) in the lower eyelid mesenchyme in (I). (J-L) Fgfr2b is expressed in the eyelid epithelium. A sense probe for Fgfr2b produces no signals (L). (M) RT-PCR analysis was conducted for mRNA purified from E15 normal eyelid mesenchyme (lanes 1, 2), E18.5 wild-type keratinocytes (lanes 3, 5), E18.5 Fgf10-null keratinocytes (lanes 4, 6), and E15 normal back skin (lane 7). Fgf10 is expressed in the eyelid mesenchyme and not by keratinocytes, while Fgfr2b is expressed by keratinocytes from wild-type and Fgf10-null fetuses. The amplification reaction was performed after incubation with (lanes 2, 5, 6, 7) or without (lanes 1, 3, 4) reverse transcriptase. co, cornea; le, lens; lld, lower eyelid; re, retina; uld, upper eyelid. Scale bars: 100 µm (A,D); 50 µm (B,C,E,F); 100 µm (H-L).