Fig. 4.

let-7 overexpression reduces pro-sensory cell proliferation and delays Atoh1 induction in the developing chicken BP. Adjacent sections of untreated control BPs (A) and let-7b-treated BPs (A,D) 18 h after electroporation and EdU treatment at E4.5. The black bars mark pro-sensory domains. (A,B) let-7b overexpression reduces pro-sensory cell proliferation. (A) Mid-apical cross-sections of let-7b-treated BP (A, right panel) and corresponding control BP (A, left panel) labeled for EdU (red) and the pro-sensory/sensory marker SOX2 (green). let-7b overexpression reduced cell proliferation both inside and outside the pro-sensory/sensory domain. (B) Quantification of A. Data are mean±s.d. (n=6 animals per group). (C,D) Adjacent cross-sections of control (C) and let-7b-treated (D) BPs through the base and mid-apex were analyzed for Atoh1, Lfng and Sox2 expression using RNA in situ hybridization. let-7b-treated BPs are malformed. (E,F) Quantification of Atoh1 (E) and Lfng (F) mRNA expression using a scoring system: 0, absent; 1, weak; 2, reduced; 3, normal expression. Four or five adjacent Atoh1- and Lfng-labeled cross-sections each representing base, mid and mid-apex were analyzed per animal and treatment. Data are mean±s.d. (n=17 animals per group). P-values were calculated using unpaired two-tailed Student's t-test (P≤0.05 is deemed significant). Ctrl, control; sac, sacculus; n, neural; a, abneural. Scale bars: 100 µm.