Chronological expression of β-gal in the brain, kidney, lung, liver, heart, and testis. (a) The brain and kidney. A–C: sagittal brain sections at 1 month did not show any positive staining signal. E–G: 12 months showed a few positively stained cells within the cerebellum (CB), where PC indicates Purkinje cells (E), and faintly stained cerebrum (Cereb), CA3 of the hippocampus, and choroid plexus (Choroid) (F). I–K: 24-month-old brain sections showed positive β-gal staining in the cerebellar folia, specifically in Purkinje cells (PC) (I), choroid plexus of the lateral ventricle (LV) (J), and CA3 (J) and substantia nigra (SN) (K). D, H, L: Photomicrographs of kidney cross-sections at different ages (1 month of age in D, 12 months of age in H, and 24 months of age in L) stained with β-gal showed strong signal in the renal cortex at 1 month, 12 months, and 24 months of age, while renal medulla remained unstained. (b) Photomicrographs of lung, liver, heart, and testis sections at different ages (1 month of age in A–D, 12 months of age in E–H, and 24 months of age in I–L) stained with β-gal. A, E, and I showed a few scattered positively stained lung cells that were observed in 1-month-old and 12-month-old lungs (arrows), and a strong signal was detected in old mouse lung bronchi (24 months of age), with a few scattered positive cells located in the alveolar epithelium (arrows). B, E, and J showed that no β-gal-positive staining was observed at any age examined in the heart. C, G, and K showed a few β-gal-positive stained cells in the liver at 12 months and 24 months of age (arrows). D, H, L: Interstitial cells of the testis were strongly positively stained for β-gal (red arrows).