Fig. 3. Immunofluorescent images of anti-PGP, trkA, trkC and p75 labeling in and around central to caudal vibrissa follicles of E15.5 wild type, trkC_K^–/– and trkC_E^–/– mice 2 days after Merkel innervation has begun to develop. Small arrows, labeled axons; large arrows, larger axon bundles; white arrowheads, Merkel endings and cells; open arrowheads, Merkel endings only; curved arrows, epidermal innervation epidermis. Brackets span locations where Merkel endings are missing or are not revealed by the particular antibody. Asterisks indicate sites of non-neuronal labeling. Inserts contain higher magnification examples of Merkel endings and cells or sites where they should be located. (A-H) In wild type and trkC_K^–/– fetuses, developing Merkel axons and endings label with anti-PGP, trkA and p75. Anti-trkA labeling is relatively faint compared with 2 days earlier (see Fig. 2C,D) and has been much more digitally enhanced than labeling in other panels. At this age only anti-PGP labels Merkel cells, which will express anti-p75 immunoreactivity within another day (see Fig. 2H). TrkC labeling is also expressed on wild-type Merkel axons and endings but is lacking on axons and endings in trkC_K^–/–. In wild type and trkC_K^–/–, non-neuronal labeling occurs with anti-p75 on dermal cells surrounding the follicles and with anti-trkC on cells within the follicles. Anti-trkC labeling within follicles is far less intense than it was 2 days earlier (see Fig. 2E,F) and has been digitally enhanced. (I-L) In trkC_E^–/– fetuses, presumptive Merkel axons label with anti-PGP, trkA and p75; however, no endings are observed with any of these labels (see inset in L). Anti-PGP also does not reveal any Merkel cells where they are seen in wild type and trkC_K^–/–. Merkel axons do not label with anti-trkC as also occurred in trkC_K^–/–. trkC_E^–/– fetuses have anti-p75 labeling on dermal cells surrounding the follicles comparable with that in wild-type and trkC_K^–/– fetuses. By contrast, the follicle cells of the trkC_E^–/– have little or no detectable trkC immunoreactivity. Scale bar: 50 µm.

Return to article