Fance deficiency impaired DNA damage repair of prospermatogonia and altered the repair dynamics of spermatocytes.

Background: Non-obstructive azoospermia (NOA) is the most severe form of male infertility and affects approximately 1% of men worldwide. Fanconi anemia (FA) genes were known for their essential role in DNA repair and growing evidence showed the crucial role of FA pathway in NOA. However, the underlying mechanisms for Fance deficiency lead to a serious deficit and delayed maturation of male germ cells remain unclear.

Methods: We used Fance deficiency mouse model for experiments, and collected testes or epididymides from mice at 8 weeks (8W), 17.5 days post coitum (dpc), and postnatal 11 (P11) to P23. The mice referred to three genotypes: wildtype (Fance ^+/+), heterozygous (Fance ^+/-), and homozygous (Fance ^-/-). Hematoxylin and eosin staining, immunofluorescence staining, and surface spread of spermatocytes were performed to explore the mechanisms for NOA of Fance ^-/- mice. Each experiment was conducted with a minimum of three biological replicates and Kruskal-Wallis with Dunn's correction was used for statistical analysis.

Results: In the present study, we found that the adult male Fance ^-/- mice exhibited massive germ cell loss in seminiferous tubules and dramatically decreased sperms in epididymides. During the embryonic period, the number of Fance ^-/- prospermatogonia decreased significantly, without impacts on the proliferation (Ki-67, PCNA) and apoptosis (cleaved PARP, cleaved Caspase 3) status. The DNA double-strand breaks (γH2AX) increased at the cellular level of Fance ^-/- prospermatogonia, potentially associated with the increased nonhomologous end joining (53BP1) and decreased homologous recombination (RAD51) activity. Besides, Fance deficiency impeded the progression of meiotic prophase I of spermatocytes. The mechanisms entailed the reduced recruitment of the DNA end resection protein RPA2 at leptotene and recombinases RAD51 and DMC1 at zygotene. It also involved impaired removal of RPA2 at zygotene and FANCD2 foci at pachytene. And the accelerated initial formation of crossover at early pachytene, which is indicated by MLH1.

Conclusions: Fance deficiency caused massive male germ cell loss involved in the imbalance of DNA damage repair in prospermatogonia and altered dynamics of proteins in homologous recombination, DNA end resection, and crossover, providing new insights into the etiology and molecular basis of NOA.