Intracellular localizations of the Dead End protein in Xenopus primordial germ cells

Abstract

We investigated the intracellular localization of Xenopus Dead end protein (Dnd1) in primordial germ cells during early development by expressing the tagged protein in transgenic Xenopus embryos, with the germ plasm visualized. Dnd1 initially localized to the germ plasm in the cortex, moved to the perinuclear region together with the germ plasm after the midblastula transition, and then entered the nucleus. Using Dnd1 deletion mutants, we identified two distinct but overlapping regions of Dnd1 that were responsible for localization to either the germ plasm or nucleus. These Dnd1 regions appeared to function in primordial germ cell-and stage-specific manners. KEY WORDS: Dnd1, germline, germ plasm, nuage, nuclear localization signal, RNA-binding proteinThe Xenopus germline is specified by inheriting a special cytoplasm, germ plasm (GP), associated with the vegetal cortex of the egg. We demonstrated that the GP was sufficient for germline specification (Tada et al., 2012). It is divided almost equally into daughter blastomeres until the 4-cell stage and is then distributed unequally to one daughter blastomere at each successive cleavage until stage 9 (Whitington and Dixon, 1975). Subsequently, it moves from the cortex to the perinuclear region and is distributed equally into two daughter primordial germ cells (PGCs). Midblastula transition (MBT), when zygotic genes begin to be expressed in most blastomeres, is observed around stage 9. However, gene expression is repressed in PGCs at MBT, so PGC specification likely occurs later (Venkatarama et al., 2010). Xpat protein, a GP component, moves from the cortex to the perinuclear region and then enters the nucleus (Machado et al., 2005). These observations suggest that some signal from GP to the nucleus is required for PGC specification.Dead end (dnd) encoding an RNA-binding protein with an RNA recognition motif (RRM) has been identified as a germlinespecific gene in vertebrates including zebrafish, Xenopus and mice (Weidinger et al., 2003). In Xenopus, the dnd1 transcript is a GP component and is required for PGC migration (Horvay et al., 2006). Furthermore, mouse dnd1 is responsible for the Ter mutant, which causes high frequency teratoma generation in a particular genetic background (Youngren et al., 2005). Several reports have described the intracellular localization of Dead end protein; in chicks Dnd protein is present in the nuclei of PGCs and mature male germ cells (Aramaki et al., 2009). In mice, two isoforms, DND1a and DND1b, were identified and localized to the nucleus and cytoplasm when Int. J. Dev. Biol. 58: 793-798 (2014) Abbreviations used in this paper: Dnd, dead end protein; GP, germ plasm; GPS, germ plasm localization signal; PGC, primordial germ cell.expressed in HeLa and COS-7 cells, respectively (Bhattacharya et al., 2007). In zebrafish, Dnd was localized to germ cell granules (GCGs, probably equivalent to Xenopus GP) in the perinuclear region of PGCs after MBT. Interestingly, this localization was dependent upon the RNA recognition motif...

Characterization of ddx4 and dnd Homologs in Snakeskin Gourami (Trichopodus pectoralis) and Their Expression Levels during Larval Development and in Gonads of Males and Females

“…For Dnd1, the deduced amino acid sequence of the Dnd1 protein contained the typical RRM and five conserved regions (NR, CR1–4). The RRM is known as the RNA-binding domain necessary for the regulation of protein localization in germ cells [ 13 , 45 , 46 , 47 , 48 , 49 ]. Phylogenetic analysis demonstrated that Dnd clustered with the Dnd families of teleosts.…”

The Role of DND1 in Cancers

“…DND1 has been detected in both the cytoplasm and nucleus [37][38][39], in line with the function of DND1 as a post-transcriptional [7,9,10,29] or transcriptional regulator [36]. What determines the multifaceted regulatory roles of DND1 is still unknown.…”

DND1 (DND microRNA-mediated repression inhibitor 1)

“…In the fertilized embryo, Dnd moves from the cortex to the perinuclear region with germplasm and enters the nucleus. It is speculated that Dnd carries RNA into the nucleus to trigger germline specification (Taguchi et al, 2014).…”