Figure 2.

Experimental Design for Assessment of Pituitary Tissue Maintenance. A, Schematic representation of mouse breeding used to generate invloxP/+;POMC-Cre mice. Homozygous female invloxP mice (23) were crossed with heterozygous male POMC-Cre mice. Mice carrying only the invloxP allele(s) are unaffected whereas mice carrying the invloxP allele will have chromosomal instability in cells expressing the POMC-Cre transgene, and these cells will be eliminated by apoptosis if they divide. B, The penetrance of POMC-Cre transgene expression was assessed by staining for POMC (green) and Cre (red) in 26-week-old pituitaries. Whereas most IL melanotropes are Cre positive, AL POMC-positive corticotropes were counted (≥ 100 cells per mouse) and scored for Cre immunoreactivity; we only counted cells with nuclei completely surrounded by POMC-positive cytoplasm. Transgene penetrance is about 53% in AL, and it is noteworthy that no ACTH-/Cre+ cells were detected. Yellow and white arrows indicate Cre-negative and Cre-positive corticotropes, respectively. Isolated red signal is caused by red blood cells autofluorescence (red arrow). C, Coimmunofluorescence staining of adult pituitary for Cre and Sox2 did not show any overlap (red arrow indicates nonspecifically stained red blood cells)..