<i>Six1;Six2</i> compound mutant genital tubercles have aberrant apoptosis patterns.

<p>(<b>A–D</b>) Comparable levels of serial of sagittal sections were stained with TUNEL for apoptotic cells (red). All sections were counter stained with DAPI (blue). (<b>E–H</b>) Ventral views of genital tubercles (GTs) stained with Lysotracker® for apoptotic cells (white dots). Apoptotic cells were observed in e11.5 control GTs within distal urethral plate epithelia (dUPE), proximal urethral plate epithelia (pUPE), distal mesenchymal (DM) (E). In <i>Six1^−/−;Six2^+/−</i> mutant, Lysotracker® signals were enhanced within dUPE and pUPE but not detectable within DM (F). Ectopic apoptotic cells in the lateral mesenchyme region (LM) was observed (E′, insert). At later stages, apoptotic cells were reduced in <i>Six1^−/−;Six2^+/−</i> mutants at e12.0 within DM (G and H). Ectopic cell death in LM persisted at e12.0 (arrowheads, H). (<b>I</b>) Schematic representations of dynamic changes of apoptosis patterns in control and mutants. CND, common nephric duct; distal mesenchymal (DM); LM, lateral mesenchyme; dUPE, distal urethral plate epithelium; pUPE; proximal urethral plate epithelium; R, rectum; see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0055587#pone-0055587-g001" target="_blank">Fig. 1</a> for more abbreviations.