Figure 6: A model for Shh-mediated integration of growth and patterning.
From: Sonic hedgehog controls growth of external genitalia by regulating cell cycle kinetics
Shh activity in wild-type (WT) and ShhcreERT2/C (mutant) genital tubercles is shown in top panel, and is based on analysis of Ptch1 expression (see Fig. 1c). During outgrowth of the genital tubercle, cell populations (red, tan, black coloured circles) defined by regionalized gene expression are exposed to secreted Shh (blue shaded areas). In wild-type genitalia, these cells divide approximately every 8.5 h and, as these progenitor pools double in number, this expands gene expression patterns. Following loss of Shh activity in mutant genitalia, cells continue to divide but cell cycle length increases to 14.4 h. This leads to a reduction in both the doubling rate of progenitor pools and the overall size of the genital tubercle. The general molecular pattern of the mutant tubercle is retained. Large red circles above and below tubercles represent the doubling time of all cells in the genital tubercle. Tc, total cell cycle time.
