(A) Intestinal progenitors stained for LIN-28∷Venus (green) and DNA (blue) from control (left), fmr1Δ50m/Δ113m mutant (middle), and esgTS/UAS-fmr1 (right) intestines. Scale bar: 10 μm. (B) LIN-28∷Venus fluorescence intensity of samples shown in (A). Significance of control versus mutant comparisons as well as numbers of samples are indicated. (C)Tub-Gal4, UAS-gfp-labeled adult control (left), fmr1Δ50m (middle), and UAS-fmr1 (right) clones generated in 7-day old adults and stained for GFP (green), LIN-28∷mCherry (red), and DNA (blue). Scale bar: 3 μm. (D) In our model, LIN-28 predominates during adaptive growth to promote the mRNA translation needed for symmetric ISC division and expansion of the progenitor population. FMRP is activated later, during the transition from growth to homeostasis, in order to recruit LIN-28 repressive mRNPs and switch the ISC division pattern from symmetric to asymmetric. See also Figure S4.