Shift of localized growth zones contributes to skin appendage morphogenesis: role of the Wnt/beta-catenin pathway - PubMed (original) (raw)

Shift of localized growth zones contributes to skin appendage morphogenesis: role of the Wnt/beta-catenin pathway

Rajas Chodankar et al. J Invest Dermatol. 2003 Jan.

Abstract

Skin appendage formation represents a process of regulated new growth. Bromodeoxyuridine labeling of developing chicken skin demonstrated the presence of localized growth zones, which first promote appendage formation and then move within each appendage to produce specific shapes. Initially, cells proliferate all over the presumptive skin. During the placode stage they are organized to form periodic rings. At the short feather bud stage, the localized growth zones shifted to the posterior and then the distal bud. During the long bud stage, the localized growth zones descended through the flank region toward the feather collar (equivalent to the hair matrix). During feather branch formation, the localized growth zones were positioned periodically in the basilar layer to enhance branching of barb ridges. Wnts were expressed in a dynamic fashion during feather morphogenesis that coincided with the shifting localized growth zones positions. The expression pattern of Wnt 6 was examined and compared with other members of the Wnt pathway. Early in feather development Wnt 6 expression overlapped with the location of the localized growth zones. Its function was tested through misexpression studies. Ectopic Wnt 6 expression produced abnormal localized outgrowths from the skin appendages at either the base, the shaft, or the tip of the developing feathers. Later in feather filament morphogenesis, several Wnt markers were expressed in regions undergoing rearrangements and differentiation of barb ridge keratinocytes. These data suggest that skin appendages are built to specific shapes by adding new cells from well-positioned and controlled localized growth zones and that Wnt activity is involved in regulating such localized growth zone activity.

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Figures

Figure1

Figure1. Localized proliferation centers (LoGZ) shift during feather morphogenesis

Skin explants were pulse labeled with BrdU (20 μm) for 30–90 min to label proliferating cells. The skins were fixed and stained with anti-BrdU antibodies. Antibodies were detected by horseradish peroxidase staining using the 3-amino-9-ethylcarbazole (AEC) substrate. The highlighted short bud shown in wholemount (a) is also shown after long-itudinal section (a’). Wholemount (a–e) and corresponding section (a’–e’) immunostaining are shown at different short bud (a,a’,b,b’), long bud (c,c’,d,d’), and follicle (e,e’) stages. Longitudinal (f) and cross (g,h) sections of an adult feather follicle are used to show filament branching and the ramogenic zone of barb ridges. The rachis in the anterior region of the follicle does not branch. Proliferation (blue arrows in b–d) can be seen in the posterior early short feather bud, distal late short bud, along the flank of the long bud and at the base of the feather follicle. PCNA staining (i–k) in the long bud (i, equivalent to d), in the forming follicle (j) and in the developed follicle (k) showed additional mesenchymal proliferation zones. Ant (anterior), Post (posterior), Pr (proximal), Di (distal), fl (flank), dp (dermal papilla), Cl (collar), bp (barb plate), rz (ramogenic zone).

Figure 2

Figure 2. In situ hybridization showing Wnt and Fz expression during the short feather bud stage

Wnt 6 wholemount in situ hybridization at E6.5 (a), E7 (b), and E8 (c). The short feather bud is shown in e and f. Wholemount staining (g) shows the shift of Wnt 6 staining in feather buds at several different stages of development (*, short bud; #, long bud; +, follicle) with feathers at each stage outlined. Wnt 6 section in situ hybridization at the placode (d) and short bud (f).Wholemount in situ hybridization expression patterns of Wnt 5a (h,i), Wnt 11 (j), Fz-1 (l), and Fz-7 (m) were also determined. Section in situ hybridization showed the distribution of Wnt 11 at the short bud stage (k). Feathers are outlined in panels a, d, and e.Wnt 5a, 6, Fz-1, and Fz-7 each were expressed in the posterior epithelium of the early short bud and the distal epithelium of the late short bud showing coexpression with the LoGZ. Wnt 11 was in the interbud epithelium and distal mesenchyme. Ant (anterior), Post (posterior), Pr (proximal), Di (distal).

Figure 3

Figure 3. In situ hybridization showing distribution of Wnt and Fz during the long feather bud stage

The distribution of Wnt 6 (a),Wnt 14 (b,e), Sfrp 2 (c),Wnt 11 (d), and Fz 1 (f). Note Wnt 6 in the barb ridges, Wnt 14 and Sfrp 2 in the flank region when LoGZ is descending. Later in the forming follicle, Wnt 14, Fz 1 and other Wnt members are in the collar region. Pr (proximal), Di (distal), bv (blood vessel), dp (dermal papilla).

Figure 4

Figure 4. Co-expression of differentiation markers with Wnt and Fz during the follicle stages

Hematoxylin and eosin staining reveals the structure of the feather follicle (a,b,j). The dermal papilla (dp) is at the base of the follicle. The collar region is above this. The papillary ectoderm (pe) descends on either side of the follicle (a). A higher power view shows the feather layers (b). The outer region is the dermal sheath (ds). The next layer is the follicle sheath (fs), then the intermediate layer (il) and basal layer (bl). A basement membrane (bm) separates the epithelium from the mesenchyme. Immunostaining shows the distribution of L-CAM (c) and neural cell adhesion molecule (e) in the developing follicle. in situ hybridization shows the distribution of β-catenin (f), Wnt 5a (g), Wnt 6 (h), Wnt 8c (i), Fz-1 (j), and Sfrp 2 (k) in the feather follicle. Barbs form at the beginning of feather branching (l). The marginal plate (mp) cells will eventually die to leave space between adjacent barbule plate (bp) epithelia. We used in situ hybridization of cytokeratin 1 (m), and feather keratin A (n) as markers. Wnt 6 (o) is in the barb ridges of the ramogenic zone.

Figure 5

Figure 5. Misexpression of Wnt 6 results in localized enlarged regions of transduced feathers

Chicken embryos were transduced with the RCAS retrovirus directing expression of control vector (a_–_f) or Wnt 6 (a’–f’) and the phenotypes were viewed in wholemount (_a,a_’) or section (b–f’). Normal feather buds are long and slender. Transduction with RCAS–Wnt 6 produced a localized enlarged region, which may be localized at the tip, the shaft, or the base of the feather filament. Sections were stained with hematoxylin and eosin (_b,b_’), PCNA (_c,c_’), terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end-labeling (_d,d_’), anti-feather keratin antibodies (_e,e_’) or anti-p27 antibody to detect the presence of the RCAS virus (_f,f_’). Note the enriched viral transduction region in the enlarged area. Proliferation was also active, but the cells could differentiate to express feather keratin. There was not much difference in terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end-labeling staining.

Figure 6

Figure 6. Schematic diagram showing the shifting LoGZ during feather morphogenesis and the involvement of the Wnt pathway

The skin forms with equal proliferation abilities throughout. Proliferation then is suspended for about 18 h as mesenchymal cells migrate and adhere to form high-density dermal condensations (Wessels, 1965). This organizes the skin into distinct bud and interbud zones. Through the action of positive and negative regulators, growth is potentiated within the newly formed buds, but continues to be suppressed in the interbud zone (Noveen et al, 1995). These are shown schematically from a top view on the top row. As the short feather buds form, proliferation becomes localized to centers, in the posterior bud (Chen et al, 1997). As the feathers grow, the LoGZ moves to the distal region in the late short bud. It then shifts through the feather flank to the base of the feather follicle during the long bud stage. In the ramogenic zone, proliferation is seen continuously in the rachidial ridge and periodically in the barb ridges. These are shown in schematic form from a side view (a). (b) A working model depicting the tentative molecular basis of LoGZ activities. It shows the potential relationship between the Wnt–β-catenin pathway and known cell proliferation related genes.

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