Fance deficiency inhibits primordial germ cell proliferation associated with transcription-replication conflicts accumulate and DNA repair defects

Fanconi anemia (FA) gene mutations are critical components in the genetic etiology of premature ovarian insufficiency (POI). Fance^-/- mice detected meiotic arrest of primordial germ cells (PGCs) as early as embryonic day (E) 13.5 and exhibited decreased ovarian reserve after birth. However, the mechanism of Fance defect leading to dysgenesis of PGCs is unclear. We aimed to explore the effect of Fance defects on mitotic proliferation of PGCs. Combined with transcriptomic sequencing and validation, we examined the effect of Fance defects on cell cycle, transcription-replication conflicts (TRCs), and multiple DNA repair pathways in PGCs during active DNA replication at E11.5 and E12.5. Results showed Fance defects cause decreased numbers of PGCs during rapid mitosis at E11.5 and E12.5. Mitotic cell cycle progression of Fance^-/- PGCs was blocked at E11.5 and E12.5, shown by decreased cell proportions in S and G2 phases and increased cell proportions in M phase. RNA-seq suggested the mechanisms involved in DNA replication and repair. We found Fance^-/- PGCs accumulate TRCs during active DNA replication at E11.5 and E12.5. Fance^-/- PGCs down-regulate multiple DNA repair pathways at E11.5 and E12.5 including the FA pathway, homologous recombination (HR) pathway, and base excision repair (BER) pathway. In conclusion, Fance defect impaired the mitotic proliferation of PGCs leading to rapidly decreased numbers and abnormal cell cycle distribution. Proliferation inhibition of Fance^-/- PGCs was associated with accumulated TRCs and down-regulation of FA, HR, BER pathways. These provided a theoretical basis for identifying the inherited etiology and guiding potential fertility management for POI.