Activate Rockstar
Gordon Neal
First of all, a CD key is an alphanumeric code that lets you download and activate a game from a distributor. It is typically found on the physical packaging of the game or in the email confirmation sent by the retailer.
That is how to activate CD keys on Rockstar Social Club. Note that once you have redeemed a game, it's yours permanently. This means you can uninstall and reinstall the game whenever you like, even if you are transferring computers. Please keep your CD key somewhere safe, in case you need to use it to settle disputes.
The oocyte-to-embryo transition culminates in the degradation of maternal transcripts and in embryonic genome activation (EGA) (Schulz and Harrison, 2019; Vastenhouw et al., 2019). The transcriptome changes prominently during the oocyte-to-four cell and four-to-eight cell transitions that are considered as the minor and major EGA stages, respectively (Braude, 1988; Petropoulos et al., 2016; Tesařk, 1988; Thnen et al., 2015; Vassena et al., 2011; Xue et al., 2013; Yan et al., 2013). In addition to the activation of key developmental genes, the non-coding genome that contributes to genome regulation becomes extensively transcribed (Bouckenheimer et al., 2016; Paloviita and Vuoristo, 2022). The activation of the embryonic transcriptome is intricately linked with major alterations in the epigenome and chromatin architecture (Chen et al., 2019; Liu et al., 2019; Wu et al., 2018; Xia et al., 2019). It is conceivable that EGA takes place only in a favorable epigenomic landscape that generates adequate conditions for timely gene regulation. How these processes are regulated in human fertilized oocytes and pre-implantation embryos, and whether the factors involved exhibit redundancy, remain poorly understood.
DUX4 belongs to a group of double homeobox genes that are unique to placental mammals. These genes are characterized by two proximal homeoboxes that encode DNA-binding homeodomains (Gabrils et al., 1999). The primate specific DUX4 is believed to have originated through retro-transposition of the ancestral DUXC gene, followed by the loss of DUXC from the primate genome (Leidenroth et al., 2012). DUX4 mRNA is enriched in human zygotes and cleavage-stage embryos (De Iaco et al., 2017; Hendrickson et al., 2017; Liu et al., 2019; Thnen et al., 2017; Vuoristo et al., 2022). Silencing of DUX4 in human embryos leads to inefficient degradation of maternal transcripts and incomplete EGA, which implies a potential role of DUX4 as an EGA regulator (Liu et al., 2022; Vuoristo et al., 2022). Human embryonic stem cells (hESCs) have been used to elucidate possible roles of selected EGA factors given the shortage of supernumerary embryos donated for research and the fact that experiments in human embryos are challenging due to ethical and technical limitations (Gawriyski et al., 2023; Hendrickson et al., 2017; Madissoon et al., 2016; Vuoristo et al., 2022; Zou et al., 2022). In hESCs, ectopic expression of DUX4 activates both coding and non-coding genes that are typically active in early human embryo at the time of EGA (Hendrickson et al., 2017; Taubenschmid-Stowers et al., 2022; Vuoristo et al., 2022; Yoshihara et al., 2022). These findings collectively suggest a pivotal role for DUX4 in regulating human EGA. In this review, we aim to provide the latest insight into DUX4 and discuss its significance in the context of human EGA.
The DUX4 open reading frames are located in the subtelomeric region of chromosome 4, within a macrosatellite repeat region known as D4Z4 (Gabrils et al., 1999) (Fig. 1). While the D4Z4 repeat array is typically epigenetically repressed in most tissues, it becomes transiently derepressed in human embryos possibly due to global epigenome reprogramming (De Iaco et al., 2017; Hendrickson et al., 2017; Liu et al., 2019; Vuoristo et al., 2022; Xia et al., 2019). The repetitive nature, high GC content, and low expression level of DUX4 pose challenges for sequencing and annotation of this genomic region, particularly when working with human embryos that are available in limited numbers. Most of our current knowledge about DUX4 stems from research on its involvement in the pathogenesis of facioscapulohumeral muscular dystrophy (FSHD) (Campbell et al., 2018). FSHD is caused by derepression of D4Z4 locus which likely leads to a burst of DUX4 expression in a subset of affected muscle cells resulting in cell death (Rickard et al., 2015; Snider et al., 2010). The derepression of D4Z4 locus is caused by either a reduction of D4Z4 repeat units alone (FSHD1), or defects in D4Z4 chromatin repressor SMCHD1 (FSHD2), or both (FSHD1+2) (Hewitt, 2015; Sacconi et al., 2019). Interestingly, a nearly identical D4Z4 repeat array exists on chromosome 10, but the contraction of this repeat array does not cause FSHD presumably due to the lack of a permissive polyadenylation signal (Lemmers et al., 2010). The toxic effect of DUX4 in FSHD pathophysiology is not yet completely understood but the mechanisms likely involve the activation of the MYC-mediated apoptotic pathway and the double-stranded RNA innate immune response pathway (Shadle et al., 2017), as well as repression of nonsense-mediated decay (NMD) (Campbell et al., 2023; Feng et al., 2015; Jagannathan et al., 2019). Notably, DUX4 is cytotoxic not only for muscle cells but also for various other cell types (Kowaljow et al., 2007; Resnick et al., 2019; Rickard et al., 2015; Wallace et al., 2011; Yoshihara et al., 2022). Given that in human embryos MYC expression is only upregulated at the time of major EGA stage, the first two days of development take place without one of the main factors behind DUX4-induced cell death. This could be one of the reasons why human embryos tolerate short-term DUX4 expression.
The protein coding DUX4 transcripts are thought to originate from the last D4Z4 repeat unit and to utilize exons distal to the repeat array that provide canonical polyadenylation signals (PAS). DUX4 transcript isoforms are generated through alternative splicing, but the regulation of this process is poorly understood. In facioscapulohumeral muscular dystrophy (FSHD) muscle, DUX4 mRNA contains exons 1-2-3, and the first intron is alternatively spliced (Snider et al., 2010). Testicular tissue expresses DUX4 mRNA isoforms with exons 1-2-4-5-6-7 and 1-2-6-7 (Snider et al., 2010). Healthy myoblasts use a cryptic splice site within the first exon and express a DUX4 mRNA isoform that is predicted to give rise to a truncated DUX4 (short DUX4 or DUX4-s) that contains the N-terminal homeodomains, but lacks the C-terminus (Snider et al., 2010). Additional DUX4 mRNA isoforms that utilize alternative polyadenylation signals are likely to exist (Smith et al., 2023). The asterisk (*) indicates the location of the translation stop codon. Abbreviations: C-term, C-terminus; DUX4, double homeobox 4; HD, homeodomain; PAS, polyadenylation signal.
Although each repeat unit in the D4Z4 array contains the DUX4 open reading frame, the current conception is that functional DUX4 transcripts originate from the last repeat unit (Fig. 1). This is explained by the position of the polyadenylation signal, which is distal to the repeat array and thus transcribed exclusively as part of the last repeat (Dixit et al., 2007). Consequently, individuals that have a contracted D4Z4 repeat region but lack the distal polyadenylation signal exhibit a normal muscle phenotype (Lemmers et al., 2010). In addition to the DUX4 mRNA isoforms that are transcribed from the D4Z4 array on chromosome 4 and use the conventional polyadenylation signal, numerous isoforms that utilize alternative polyadenylation sites have been described to originate from both chromosome 4 and 10. These isoforms likely result from alternative splicing, however the mechanisms that control the splicing of DUX4 transcripts remain obscure. Moreover, it is unclear which mRNA isoforms give rise to functional DUX4 proteins. Testis and some cancer cell lines express DUX4 transcripts that most likely produce a complete DUX4, as indicated by immunofluorescence stainings and the activation of DUX4 target genes (Smith et al., 2023; Snider et al., 2010). In contrast, various somatic tissues, including healthy muscle, express low levels of capped and polyadenylated DUX4 transcript isoform, which probably produces a truncated protein that lacks the transcription activation domain and, consequently, the ability to activate DUX4 targets (Snider et al., 2010). DUX4 mRNA isoforms present in human embryos have not been described.
In accordance with the timing of the nuclear localization of DUX4 (Vuoristo et al., 2022), the accessible genomic regions in 2-cell and 4-cell embryos are enriched with DUX4 binding motifs (Hendrickson et al., 2017; Liu et al., 2019; Wu et al., 2018). Accessible chromatin regions in human cleavage stage embryos are frequently located at distal sites (> 5 kb from the transcriptional start sites) of genes and enriched at TEs (Gao et al., 2018; Liu et al., 2019; Wu et al., 2018). TEs are mobile genetic elements constituting approximately half of the human genome (Franke et al., 2017). TEs are enormously diverse and divided into distinct classes and families based on their modes of transposition, structural features, and evolutionary relationship (Bourque et al., 2018). TEs promote genetic diversity by moving within the genome, which can lead to alterations in host genes and regulatory sequences. This mobility poses a significant risk to genome stability, and therefore several mechanisms have evolved to suppress TEs (Almeida et al., 2022).
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