Immunostaining of testicular sections with PCNA and quantification of proliferating germ cells and levels of serum FSH and testicular testosterone. Proliferating germ cells in testicular sections from a mouse exposed to bortezomib 45 days earlier (A) and a corresponding control (B) labeled with brown color (arrows) after immunostaining with PCNA antibody. Quantification of proliferating germ cells per seminiferous tubule in all treated and pup groups, and their respective controls (C). Lower panels show serum FSH (D) and testicular testosterone (E) levels in 2 days, 45 days, and 6 months follow-up mice and pups of bortezomib treated animals and their corresponding controls. Magnification in (A) and (B) is 20×. Ctl: control, Bort: bortezomib. PCNA: proliferating cell nuclear antigen.