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Comparative Study
. 2004 Sep 3;305(5689):1465-6.
doi: 10.1126/science.1098109.

Molecular shaping of the beak

Ping Wu  1 , Ting-Xin Jiang, Sanong Suksaweang, Randall Bruce Widelitz, Cheng-Ming Chuong
Affiliations
Comparative Study

Molecular shaping of the beak

Ping Wu et al. Science. .

Abstract

Beak shape is a classic example of evolutionary diversification. Beak development in chicken and duck was used to examine morphological variations among avian species. There is only one proliferative zone in the frontonasal mass of chickens, but two in ducks. These growth zones are associated with bone morphogenetic protein 4 (BMP4) activity. By "tinkering" with BMP4 in beak prominences, the shapes of the chicken beak can be modulated.

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Figures

Figure 1
Figure 1. Cell proliferation and BMP4 function in chicken and duck beak morphogenesis
(A) Stage 36 chicken and duck beaks, top view. Blue, cartilages. Red, bones. Double headed arrows indicates beak tip width (fig. S2E). (B) Stage 27 frontal sections. 1.5 hr BrdU labeling. See fig. S1C for stages 26, 28, 29 and 31. Percent BrdU positive cells were quantified in 9 regions using the grid overlay (11) shown in table S1. Arrow indicates the rostral margin. (C) Three dimensional reconstruction of the percent BrdU positive cells in the FNM. Red >20%, yellow 10-20%, green <10%. From this perspective, viewing the inner red zone through the yellow zone appears orange. Purple indicates proliferation in the cartilage region. (D) BMP4 RT-PCR from stage 25 FNMs showed a higher BMP4/GAPDH ratio in ducks than in chickens. (E) Left panel: Stage 37 control. Middle and right panels: RCAS BMP4 or RCAS noggin were injected into all beak prominences of chicken embryos and harvested at Stage 37. Arrows point to enlarged skeletal elements. (F) Left panel: Stage 20 chicken FNM was divided into three regions (a-c, defined in fig. S2B). Excision of region b containing the frontonasal ectodermal zone and subjacent mesenchyme (insert) truncated the upper beak with missing distal cartilage elements as observed at stage 36. Ablation of region a or c showed normal growth (not shown). Middle panel: BMP4 beads (insert, red circle) can rescue most growth and cartilage elements from region b ablated specimens (stage 37). Right panel: BMP4 bead addition to non-ablated FNM led to wider upper beaks (stage 36). FNM, frontonasal mass; mc, Meckel's cartilage; MXP, maxillary prominence; n, nasal bone; nc, nasal chonchae; pmx, premaxilla bone; pnc, prenasal cartilage. Size bars, 1mm.
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