LAUSR

Abstract Fanconi anemia complementation group B (FANCB) protein is a major component of the Fanconi anemia (FA) core complex and plays an important role in hematopoiesis and germ cell development. Deletion of Fancb gene causes the defect of primordial germ cell (PGC) development and infertility in male mice. However, it remains unknown whether Fancb is required for female germ cell development. In this study, we found that the fertility of Fancb knockout male mice in C57/ICR mixed backgrounds was not affected. Female Fancb–/– mice were obtained by crossing Fancb+/– females with Fancb–/Y males. The number of PGCs was dramatically decreased in Fancb–/– females. Very few oocytes were observed after birth and the primordial follicle pool was completely depleted at 6 weeks of age in Fancb–/– females. However, the remained oocytes from Fancb–/– mice were normal in fertilization and embryonic development from 2-cell to the blastocyst stage. We also found that Fancb and Fancl double-knockout males were also fertile and the number of sperm in epididymis was not reduced as compared to that of Fancb–/– and Fancl–/– single-knockout mice. Taken together, these results showed that Fancb is also essential for female germ cell development. Inactivation of Fancb causes massive germ cell loss and infertility in adult females. We also found that Fancb and Fancl do not act synergistically in regulating germ cell development. Summary Sentence Fancb plays an essential role in the maintenance of germ cell development in female gonads and is a potentially causative gene for premature ovarian insufficiency. Graphical Abstract