Fig. 9. Molecular events leading to defective spermatogenesis in Brca1 full-length isoform-deficient mice. Two major functions of Brca1 during spermatogenesis are empahasized: (1) recruiting DNA damage-repair proteins to damage sites; and (2) regulating RNA expression of genes involved in DNA-damage repair. Absence of the full-length isoform of Brca1 results in impaired DNA-damage repair and leads to the termination of spermatocyte development at the pachytene stage by p53-dependent and p53-independent apoptosis.