Fig. 2. Deletion of IKK2 in mammary gland results in reduced apoptosis and delayed involution. (A) Haematoxylin and eosin staining of mouse mammary gland sections from Cre^-, Cre⁺/Ikk2^fl/wt or Cre⁺/Ikk2^fl/fl mice at 0dL, 24, 48, 72 or 144 hours' involution. Apoptosis is apparent in glands from Cre^- control mice that subsequently underwent remodelling normally. Apoptotic cells are seen to accumulate in the open lumen of the lobuloalveolar structures (<). Involution and remodelling was delayed in the glands from Cre⁺/Ikk2^fl/wt mice. This delay was more pronounced in Cre⁺/Ikk2^fl/fl glands. By 6 days' involution very little difference is seen between mice of the different genotypes. (B) Cleavage of caspase 3 was determined by immunofluorescence in mammary gland sections from Cre^-, Cre⁺/Ikk2^fl/wt or Cre⁺/Ikk2^fl/fl mice at 24, 48 or 72 hours' involution. (green: cleaved caspase-3-positive cells; red: DAPI-stained nuclei). TUNEL staining at 72 hours' involution showed a higher proportion of positive (green) cells in Cre^- and heterozygous glands. (C) Cleaved caspase-3-positive cells were expressed as a percentage of total cell number and data presented in graphical format. Approximately 10,000 cells were counted. Cleaved caspase 3 levels peaked at 24 hours' involution in Cre^- glands, was delayed by 48 hours in Cre⁺/Ikk2^fl/wt mice and remained constant at all involution timepoints in Cre⁺/Ikk2^fl/fl mice. Scale bars: 100 µm.