Fig. 5. Changes of hair filament differentiation in Msx2 knockout mice. (A,B) Plucked hairs from Msx2 knockout mice are short and curly, reflecting defects in hair structures. Scale bar: 100 µm. (C,D) Medulla patterning is affected as suggested by the irregular septations in the hair. Scale bar: 50 µm. (E-H) Scanning EM showing unevenness in diameter of Msx2 knockout mice hairs. Cuticles fail to form, resulting in a smooth, wrinkled surface. Scale bar: 30 µm in E,F; 10 µm in G,H. (I,J) Trunk hairs from wild-type (I) and Msx2 knockout (J) mice. Both club ends are morphologically similar (arrowheads). Septation patterns are irregular in the mutants, but there are no breakages in the middle of the shaft. Scale bar: 100 µm. (K,L) BrdU labeling was performed at P5, P9, P11 and P15, and representative panels from P11 are shown. BrdU-positive cells were detected in both the hair matrix and the outer root sheath (arrows). Quantitation of BrdU-positive cells in the matrix showed similar levels of incorporation in the mutants. (M,N) Apoptotic cells detected by TUNEL assay carried out at P5, P9, P11, P14 and P30 (an example is shown from P30). Positive cells were observed in epidermis and dermis. No apparent differences between wild-type and Msx2 knockout mutant skins were observed. Scale bars: 250 µm.

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