SRP126106 PRJNA421016 GSE107682 Tdrd6a recruits Ziwi-bound piRNAs and coordinates deposition of germ plasm mRNAs into primordial germ cells [small RNA] Germ plasm, the Balbiani body and nuage are evolutionary conserved structures essential for germ cell specification and maintenance. We describe Tdrd6a as a component of these structures with two distinct molecular functions. First, Tdrd6a facilitates the accumulation of the typical antisense-bias of piRNAs, without having effects on piRNA biogenesis signatures. Second, we show that Tdrd6a is required for Balbiani body and germ plasm integrity, and associates with RNA-binding proteins and germ plasm mRNAs. On the cell-biological level, maternally contributed Tdrd6a strongly impacts germ cell formation, but is dispensable for fertility. Using single-cell RNA-sequencing we demonstrate that Tdrd6a promotes early germ cell development and regulates the stoichiometry of germ plasm mRNAs. We propose that Tdrd6a functions as a scaffold to recruit correct ratios of germ plasm transcripts and to accumulate antisense piRNA complexes in order to ensure both specification and maintenance of germ cells. Overall design: Zebrafish were grown under standard conditions. Total ovary or size selected Oocytes were used to extact RNA from het of tdrd6a mutant fish. GSE107682 pubmed 30086300 parent_bioproject PRJNA315403