Figure 4. Spermatid differentiation proceeds in the presence of BI2536. (A) Control and BI2536-treated spermatids expressing Unc-GFP (green) were counterstained for acetylated-tubulin (red) and DNA (blue). Control spermatids inherit only one centriole at the end of meiosis (arrow), whereas BI2536-treated spermatids inherit 2 pairs of orthogonal centrioles (double arrow). In both control and treated spermatocytes the beginning of axoneme formation is marked by the detachment of the distal Unc-GFP dots (arrowheads) that gradually move away from the centriole. (B) The centrioles have a distal cilium-like structure in both control and treated spermatids; treated spermatids display pairs of engaged centrioles. (C) Control spermatids have 9+2 axonemes, whereas treated spermatids display the conventional model together with abnormal axonemes. Scale bar = 2.5 μm in (A); 250 nm in (B); 100 nm in (C).