Functional Study Of Igf2bp3 In Zebrafish Embryonic Development

Early embryogenesis relies on maternally inherited m RNAs.Although the mechanism of maternal m RNA degradation during maternal-to-zygotic transition(MZT)has been extensively studied in vertebrates,how the embryos maintain maternal m RNA stability remains unclear.Here,we identified Igf2bp3 as an important regulator of maternal m RNA stability in zebrafish.Depletion of maternal igf2bp3 destabilized maternal m RNAs prior to MZT and led to severe developmental defects,including abnormal cytoskeleton organization and cell division.However,the process of oogenesis and expression levels of maternal m RNAs in unfertilized eggs were normal in the maternal igf2bp3 mutants.Gene ontology revealed that these functions were largely provided by Igf2bp3-bound m RNAs.Indeed,Igf2bp3 depletion destabilized while its overexpression enhanced its targeting maternal m RNAs.Interestingly,igf2bp3overexpression in the wild-type embryos also caused a developmental delay.Altogether,these findings highlight an important function of Igf2bp3 in controlling early zebrafish embryogenesis by binding and regulating the stability of maternal m RNAs.The Bucky ball(Buc)has been implicated in germ plasm(GP)assembly during early zebrafish development via regulating GP-m RNA expression,but the precise mechanism underlying how Buc modulates this process has remained unknown.Here,we report a m~6A reader Igf2bp3 interacts and co-localizes with Buc in the germ plasm.Similar to loss of Buc,genetic deletion of maternal igf2bp3 in zebrafish leads to abnormal GP assembly and insufficient germ cell specification,which could be partially restored by injection of igf2bp3 m RNA.Mechanistically,Igf2bp3 binds to m~6A-modified GP-organizer-and GP-m RNAs in an m~6A-dependent manner and prevents their degradation.These findings reveal that Igf2bp3 as direct effector protein of Buc functions in GP-m RNA expression and germ plasm assembly through m~6A-dependent regulation and highlight a critical role of m~6A modification in the process of germ plasm assembly.In conclusion,igf2bp3 is required for maintaining maternal RNAs and germ plasm assembly during the early embryo development.