Fig. 3. Blimp1 function in progenitors of the dermal papillae is
required for induction of the sensory vibrissae. At E18.5, wild-type
(A) embryos display five prominent rows of sensory vibrissae. These are
completely absent from mutants (B). Frontal sections through control
(C) and mutant (D) E16.5 embryos demonstrate missing vibrissae
but normal tongue and tooth development. (E) Blimp1
transcripts are strongly expressed in the forming vibrissae at E12.5.
(F) Shh transcription is activated but not maintained in
Blimp1 mutants. (G-I) Blimp1 together with
Bmp4 and Shh marks the mesenchymal condensates of the
forming vibrissae at E12.5. Fate-mapping studies identify Blimp1+
cells as giving rise to the initial condensates of the prospective dermal
papilla (J), and underlie the invaginating ectodermal placodes
(K), ultimately giving rise to the mature DP (L).
Blimp1+ cells that fail to incorporate into the DP migrate to
surround the shaft of the forming follicle. (M) Fate-mapping studies
show Blimp1+ cells give rise to the DP of the coat hair follicles and
intrafollicular mesenchyme of the E18.5 back skin. (J,M) Punctuate
lacZ staining marks endothelial cells. However in marked contrast to
the vibrissae, histological analysis shows that hair follicle induction is
Blimp1 independent (N,O). Ki67 staining at E12.5 shows
that Blimp1 expressing cells of the dermal condensate (P), and
DP (Q,R) are quiescent, whereas cells of the surface ectoderm,
the ectodermally derived hair shaft and surrounding mesenchyme are strongly
labelled. (S) Ki67 labelling is uniform in the mesenchyme of
Blimp1 deficient embryos. (T) In wild-type embryos c-myc is
detected in the surrounding mesenchyme but not in the prospective DP.
(U) c-myc-positive cells are uniformly scattered throughout both the
mesenchyme and surface ectoderm in sites of vibrissae induction in
Blimp1 mutants. en, endothelial cells; dc, dermal condensates; dp,
dermal papillae; hf, hair follicle; ifd, interfollicular demis; v, vibrissae;
N, nares; T, teeth; Tg, tongue; VNO, vomeronasal organ.