Fig. 7. Epifluorescence images of anti-PGP, p75, trkA or trkC labeling (red) combined with transmitted light images of lacZ reporter gene labeling (blue) in and around rostral and caudal vibrissa follicles of E14 and E15 mouse fetuses. Fetuses have either a homozygous (Ntf3^lacZ/lacZ) or heterozygous (Ntf3^+/lacZ) lacZ reporter gene substitution for Ntf3. Small arrows indicate labeled axons; large arrows, larger axon bundles; white arrowheads, Merkel endings and cells; open arrowheads, only Merkel endings. Asterisks indicate sites of non-neuronal p75 or trkC expression. (A-F) At E14, Ntf3/lacZ is expressed only in the dermis completely surrounding less mature rostral follicles (between curved arrows in A and D). Among more mature caudal follicles (B,C,E and F), Ntf3/lacZ is expressed in a restricted zone (between broad arrows) at mid-levels inside the follicles as well as in the dermis only surrounding the upper end of the follicles (between curved arrows). The pattern of Ntf3/lacZ expression is similar in homozygotes (B and E) and heterozygotes (C and F) but follicles of heterozygotes are larger and more mature. Only the upper two thirds of follicles are shown in C and F. Among the relatively immature follicles of homozygotes, anti-trkC labeling is present on cells throughout the follicles (A) whereas anti-p75 labeling is present on dermal cells surrounding the follicles (D). Non-neuronal expression of trkC has begun to decrease within more mature caudal follicles of homozygotes (B) and has nearly disappeared in relatively more mature caudal follicles of the heterozygote (C). In homozygotes and heterozygotes, Merkel innervation labels with anti-p75. Labeled endings are present only at the site where Ntf3/lacZ is expressed within the follicles (E,F). No innervation labels with anti-trkC in homozygotes (open arrow), but some axons (small arrow) and endings (open arrowhead) are trkC positive in heterozygotes (inset, C). The insets in C and E are enlargements of areas bounded by white rectangles but the blue lacZ label has been digitally suppressed and the red anti-trkC and anti-p75 label digitally enhanced. (G-J) In E15 Ntf3^lacZ/lacZ or Ntf3^+/lacZ fetuses, Ntf3/lacZ is intensely expressed primarily in the dermis surrounding upper ends of follicles and, compared to E14, is substantially reduced within the mid-level of follicles. Neuronal and non-neuronal labeling with anti-trkA (G) and anti-p75 (not shown) are comparable to normal (see Figs 2, 6). In homozygotes (H), anti-trkC labels the core of the follicle where the vibrissa is developing but does not label any innervation. Anti-PGP labels Merkel endings and cells at mid-follicle levels in homozygotes and heterozygotes (I and J). Scale bar: 50 µm.

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