BTBR mice exhibit reduced cellular proliferation in the midline and neocortex at E17 corresponding to a reduction in progenitor cells. E17 control (A) and BTBR (B) mice (n ≥6) were injected with EdU 30 minutes prior to sacrifice and immunolabeled for nuclear marker DAPI (white), EdU (green), phospho-histone H3 (PH3, blue), and Ki67, Pax6, or Tbr2 (red). Cell counts were performed for single, double, and triple-labelled cells, where data for all counts are shown in Additional file 2: Figure S2. Representative regions from the midline of control (C-E) and BTBR (F-H) mice demonstrate that BTBR mice have reduced incorporation of EdU into Tbr2-positive cells, as quantified in (Q). Furthermore, BTBR mice show reduced incorporation of EdU into mitotic cells (PH3-positive), and radial glia (Pax6-positive) in the neocortex (L-N) as compared to control animals (I-K, quantified in R). No differences in cellular proliferation were observed in the ganglionic eminence between control (O), and BTBR mice (P). Scale bar in B represents 500 μm for A-B. Scale bar in J represents 100 μm for E-J. Scale bar in Q represents 100 μm for K-M, O-Q. Scale bar in R represents 100 μm for N and R. Mann-Whitney U test for significance: ***P <0.001. Data are presented as mean ± SEM. (E17: Embryonic day 17; EDU, 5-Ethynyl-2′-deoxyuridine; DAPI, diamidino-2-phenylindole; Pax6, Paired Box 6; Tbr2,T-Box Brain Protein 2).