Building RNA-protein germ granules: insights from the multifaceted functions of DEAD-box helicase Vasa/Ddx4 in germline development

Abstract

The segregation and maintenance of a dedicated germline in multicellular organisms is essential for species propagation in the sexually reproducing metazoan kingdom. The germline is distinct from somatic cells in that it is ultimately dedicated to acquiring the "totipotency" and to regenerating the offspring after fertilization. The most striking feature of germ cells lies in the presence of characteristic membraneless germ granules that have recently proven to behave like liquid droplets resulting from liquid-liquid phase separation (LLPS). Vasa/Ddx4, a faithful DEAD-box family germline marker highly conserved across metazoan species, harbors canonical DEAD-box motifs and typical intrinsically disordered sequences at both the N-terminus and C-terminus. This feature enables it to serve as a primary driving force behind germ granule formation and helicase-mediated RNA metabolism (e.g., piRNA biogenesis). Genetic ablation of Vasa/Ddx4 or the catalytic-dead mutations abolishing its helicase activity led to sexually dimorphic germline defects resulting in either male or female sterility among diverse species. While recent efforts have discovered pivotal functions of Vasa/Ddx4 in somatic cells, especially in multipotent stem cells, we herein summarize the helicase-dependent and -independent functions of Vasa/Ddx4 in the germline, and discuss recent findings of Vasa/Ddx4-mediated phase separation, germ granule formation and piRNA-dependent retrotransposon control essential for germline development. Keywords DEAD-box helicase • Germline • Transposable elements (TE) • Phase separation • Spermatogenesis • Spermiogenesis • piRNA Cellular and Molecular Life Sciences * Jianqiang Bao

The Beginning of Meiosis in Mammalian Female Germ Cells: A Never-Ending Story of Intrinsic and Extrinsic Factors

“…MVH is an ATP-dependent RNA helicase that often changes the secondary structures of RNA during processes such as alternative splicing and protein translation initiation [ 97 ]. MVH interacts with ribonucleic acids through its conserved DEAD (Asp-Glu-Ala-Asp)-RNA-binding motif and exerts multiple roles in the germline of various species [ 98 ]. For example, it appears to be able to regulate the proliferation and pluripotency of PGCs and meiosis in male germ cells; however, no specific functions of the protein in mammal oogenesis were found.…”

The germline factor DDX4 contributes to the chemoresistance of small cell lung cancer cells

“…1a ). Since many germline factors, including ddx4 and piwi , are known to undergo extensive post-transcriptional and post-translational regulation 25 , 31 , mRNA expression may not necessarily reflect their protein expression levels. Therefore, its expression was also confirmed by the immunoblot (Fig.…”

Vasa, a regulator of localized mRNA translation on the spindle

“…Vasa has multiple functional domains with zinc-finger domains in the N-terminus and core helicase domains in the center and C-terminus (Figure 4A). Various Vasa mutants have been made, especially in the central helicase domain containing the "DEAD" sequence of Vasa, which were mostly tested in Drosophila or mice (see a comprehensive summary table in Xu et al, 2021). [44] These Vasa mutants are known to cause sterility in female flies or male mice and/or compromise piRNA biogenesis in the resultant animals, suggesting the essentiality of the core helicase domain for its function.…”

“…Various Vasa mutants have been made, especially in the central helicase domain containing the "DEAD" sequence of Vasa, which were mostly tested in Drosophila or mice (see a comprehensive summary table in Xu et al, 2021). [44] These Vasa mutants are known to cause sterility in female flies or male mice and/or compromise piRNA biogenesis in the resultant animals, suggesting the essentiality of the core helicase domain for its function. However, over 35 DDX family proteins are present, and the multiple functional domains are conserved across the DDX family proteins.…”