DNA repair protein FANCD2 has both ubiquitination-dependent and ubiquitination-independent functions during germ cell development

When DNA interstrand crosslink lesions occur, a core complex of Fanconi anemia proteins promotes the ubiquitination of FANCD2 and FANCI, which recruit downstream factors to repair the lesion. However, FANCD2 maintains genome stability not only through its ubiquitination-dependent but also its ubiquitination-independent functions in various DNA damage response pathways. Increasing evidence suggests that FANCD2 is essential for fertility, but its ubiquitination-dependent and ubiquitination-independent roles during germ cell development are not well characterized. In this study, we analyzed germ cell development in Fancd2 KO and ubiquitination-deficient mutant (Fancd2(K559R/K559R)) mice. We showed that in the embryonic stage, both the ubiquitination-dependent and ubiquitination-independent functions of FANCD2 were required for the expansion of primordial germ cells and establishment of the reproductive reserve by reducing transcription-replication conflicts and thus maintaining genome stability in primordial germ cells. Furthermore, we found that during meiosis in spermatogenesis, FANCD2 promoted chromosome synapsis and regulated crossover formation independently of its ubiquitination, but that both ubiquitinated and nonubiquitinated FANCD2 functioned in programmed double strand break repair. Finally, we revealed that on meiotic XY chromosomes, H3K4me2 accumulation required ubiquitination-independent functionality of FANCD2, while the regulation of H3K9me2 and H3K9me3 depended on FANCD2 ubiquitination. Taken together, our findings suggest that FANCD2 has distinct functions that are both dependent on and independent of its ubiquitination during germ cell development.