Tdrd1/Mtr-1 , a tudor -related gene, is essential for male germ-cell differentiation and nuage/germinal granule formation in mice

Abstract

Embryonic patterning and germ-cell specification in mice are regulative and depend on zygotic gene activities. However, there are mouse homologues of Drosophila maternal effect genes, including vasa and tudor, that function in posterior and germ-cell determination. We report here that a targeted mutation in Tudor domain containing 1͞mouse tudor repeat 1 (Tdrd1͞Mtr-1), a tudor-related gene in mice, leads to male sterility because of postnatal spermatogenic defects. TDRD1͞MTR-1 predominantly localizes to nuage͞ germinal granules, an evolutionarily conserved structure in the germ line, and its intracellular localization is downstream of mouse vasa homologue͞DEAD box polypeptide 4 (Mvh͞Ddx4), similar to Drosophila vasa-tudor. Tdrd1͞Mtr-1 mutants lack, and Mvh͞Ddx4 mutants show, strong reduction of intermitochondrial cement, a form of nuage in both male and female germ cells, whereas chromatoid bodies, another specialized form of nuage in spermatogenic cells, are observed in Tdrd1͞Mtr-1 mutants. Hence, intermitochondrial cement is not a direct prerequisite for oocyte development and fertility in mice, indicating differing requirements for nuage and͞or its components between male and female germ cells. The result also proposes that chromatoid bodies likely have an origin independent of or additional to intermitochondrial cement. The analogy between Mvh-Tdrd1 in mouse spermatogenic cells and vasa-tudor in Drosophila oocytes suggests that this molecular pathway retains an essential role(s) that functions in divergent species and in different stages͞sexes of the germ line.

Tudor domain containing 7 ( Tdrd7 ) is essential for dynamic ribonucleoprotein (RNP) remodeling of chromatoid bodies during spermatogenesis

“…S3 K-R), which contrasted to the meiotic catastrophe of Tdrd1 −/− and Tdrd9 −/− spermatocytes (Fig. S3 S-Z) (5,9). Thus, Tdrd7 and Tdrd6 constitute a spermiogenic class of tudor family genes, which function in a sequential and nonredundant manner.…”

“…Mammals possess homologs of such genes, including vasa, tudor, piwi, and mael, and these gene products are also localized in mammalian germinal granules (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13). Such germline-specific and conserved composition suggests that germinal granules are a bona fide feature that characterizes the germline.…”

“…We previously showed that tudor domain-containing (TDRD) proteins, including TDRD1, -6, -7, and -9, constitute conserved components of chromatoid bodies in mice (5,6,9,10). TDRD1 binds to arginine dimethylated MILI, a mouse piwi protein; TDRD9 associates with MIWI2, another essential piwi protein; and the two Tdrd members cooperate in the piwi-interacting RNA (piRNA) pathway to establish retrotransposon silencing in fetal prospermatogonia (4,9,12,17,18).…”

Mouse Piwi interactome identifies binding mechanism of Tdrkh Tudor domain to arginine methylated Miwi

“…For example, a single multiTudor protein, such as Tdrd1 or Tdrd6, could simultaneously engage multiple sites on the same Piwi protein through its individual Tudor domains, or could cross-link distinct Piwi proteins; conversely, each Piwi protein with multiple methylated arginines could recruit Tudor domains from different Tudor proteins. Proteins with tandem Tudor domains may therefore serve as scaffolds that form multipoint contacts with Piwi proteins, and thereby coordinate the formation and operation of the nuage/chromatoid body important for germ cell differentiation and development (7,9,29).…”

“…S1). While the physiological functions of germline proteins with a single Tudor domain (Tdrkh, Tdrd5, Stk31, and Tdrd9) are largely unknown, mouse knockout studies of Tdrd1, Tdrd4, and Tdrd6 have revealed crucial roles for these multiTudor domain proteins in nuage/chromatoid body formation, spermatogenesis, and small RNA pathways (7)(8)(9). However, the binding properties of these germline Tudor proteins are poorly understood.…”