Dead-End mimic helicase activity to promote manos translation in the germline

AGÜERO, TRISTAN H.; ZHIGANG JIN; OWENS, DAWN A.; MALHOTRA, ARUN; YANG, JING; KING, MARY LOU

Portland, Oregon

Congreso; SDB 77th Annual Meeting; 2018

Primordial germ cells (PGCs) constitute theexclusive progenitors of the gametes in the developing embryo. PGCs maintaintheir totipotency even upon differentiation into highly specialized gameticcells. Preserving full potential is an essential attribute of PGCs and isrequired for the survival of all sexually reproducing species. The germ celllineage in Xenopus is specified by the inheritance of germ plasm that assembleswithin the Balbiani body in stage I oocytes. Specific RNAs, such as nanos1,localize to the germ plasm. nanos1 has the central germline function ofblocking somatic gene expression and thus preventing PGC loss and sterility. Itis unclear how Nanos translation is regulated in developing embryos. We reporthere that nanos1 translation after fertilization requires Dead-end 1 (Dnd1), avertebrate-specific germline RNA-binding protein. Dnd1 expression is restrictedto the vertebrate germline where it is believed to activate translation of RNAsrequired to protect and promote that lineage. nanos1 is one such germline RNAwhose translation is blocked by a secondary RNA structure in the ORF. Dnd1 containsa canonical RNA Recognition Motif (RRM1) in its N-terminus but also a lessconserved RRM2.  Here we provide a mechanistic picture of nanos1 RNA-Dnd1interaction. Dnd1 possesses ATPase activity. Surprisingly this activity ismapped within the RRM2, different from the C-terminal region where it was firstfound in zebrafish. More importantly, we show that while RRM1 is required forbinding nanos1, RRM2 is required for nanos1 translation and germline survival.Further, Dnd1 functions as a homodimer and binds nanos1 RNA just downstream ofthe secondary structure required for nanos1 repression. We propose a modelwhere the RRM1 is required to bind nanos1 RNA while the RRM2 is required topromote translation through the action of ATPase. This work uncovers a noveltranslational regulatory mechanism that is fundamentally important for germlinedevelopment.