Fig. 5. Defective cytokinesis in CIT-K^-/- undifferentiated male germ cells. (A,B) Semi-thin sections of P4 CIT-K^+/+ (A) and ^-/- (B) testes were analyzed by optical microscopy. Red arrowheads point to type A spermatogonia displaying more than one nucleus. (C) The percentage of undifferentiated germ cells displaying a binucleate/multinucleate morphology was determined on semi-thin sections by optical microscopy. Error bars show standard deviation, P<0.005. (D) Electron microscopy picture of a P4 CIT-K^-/- type A spermatogonium, displaying three nuclei surrounded by the same cytoplasm. (E) Anti-cyclinD1 immunohistochemistry performed on P4 CIT-K^-/- testis, showing a multinucleated spermatogonium expressing high levels of this protein. (F) High-power field of anti-activated Caspase-3 immunostaining, performed on P4 CIT-K^-/- testis. Red arrowhead indicates an early apoptotic, binucleate cell. Bars, 20 µm.