The toku phenotype results from a mutation in Gk5. (A) Representative adult homozygote toku mouse exhibiting alopecia. (B) Delayed hair growth in a representative toku homozygote (Top Right) at P10; a littermate wild-type mouse is shown at the Bottom Left. (C) Toku homozygotes exhibit hair loss that progresses with age beginning as early as P14; representative toku mouse is shown for each time point. (D) Hair follicle morphogenesis and cycling in wild-type (+/+) and toku homozygotes. Upper back skin from mice of the indicated ages was fixed, sectioned longitudinally to the hair shaft, and stained with H&E. Representative sections from wild-type (a–d) or toku homozygous mice (e–h) were imaged at 40× (a and e) or 100× magnification (b–d, f–h). Insets are enlargements of the boxed areas. (Scale bars, 100 μm.) (E) Skin grafted from a wild-type mouse onto a homozygous toku mouse and from a homozygous toku mouse onto a wild-type mouse 35 d posttransplantation. Skin grafted from a wild-type mouse onto a wild-type mouse and from a homozygous toku mouse onto a homozygous toku mouse were included as controls. All of the images shown are representatives from at least three repeated experiments. (F) DNA sequence chromatogram of the deleted nucleotide in Gk5. (G) The phenotype of three Gk5-TALEN founders. The DNA sequence of each of the TALEN-induced mutations in the founders is shown in Fig. S2C. (H) Domain structures of isoform 1 (GK5-v1) and isoform 2 (GK5-v2) of mouse GK5. The putative locations of the FGGY_N, FGGY_C, catalytic cleft, and ATP-binding domains, as predicted by SMART and UniProt, are indicated. The locations of the toku, barrener, and tangyuan mutations are indicated in GK5-v1; the mutations affect similar regions in both isoforms. The barrener and tangyuan mutations affect splice donor sites. (I) Immunoblot analysis of exogenously expressed FLAG-tagged GK5-v1, FLAG-tagged GK-v2, and a truncated FLAG-tagged GK5 (GK5-toku; amino acids 1–174) from HEK293T cells using antibodies against FLAG and GFP. GFP was probed as a transfection efficiency control.