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  • There exist two different known mechanisms of protein synthe

    2018-11-12

    There exist two different known mechanisms of protein synthesis from mRNA template: cap-dependent and cap-independent translation initiation. The latter is driven by IRES element that was found in both viral RNAs and cellular mRNAs (Balvay et al., 2009; Shatsky et al., 2010). IRES element was originally discovered in the picornaviral RNA translation process. Viral RNA folds into specific RNA structure to mimic the ribosome scaffold and then recruits ribosomal subunits and translational factors, subsequently starts the elongation process. With reduction of protein involvement and less steps, cap-independent translation dominates when the canonical cap-dependent pathway is interrupted (Fernandez-Miragall et al., 2009; Jackson, 2005). IRES-mediated translation represents a cellular “backup” pool, leading to cell survival or cell death under unfavorable conditions and it confers a regulation mechanism of selective translation at the posttranscriptional level. And this process makes cell respond quickly to rapid changes (Komar & Hatzoglou, 2005; Kozak, 2005). In concordance with other reports (Cheng et al., 2007; Farashahi Yazd, et al., 2011; Karoubi, et al., 2010; Mizuno and Kosaka, 2008), in this study, we illustrated Oct4B-190aa mainly expressed in cytoplasma, although it had nuclear localization signal in POU domain, and the underlying mechanism still need to be further investigated. Meanwhile Oct4B-190aa expression level was upregulated under heat shock and oxidative conditions, suggesting that it was involved in the stress response activity. In conclusion, mouse Oct4 gene, regulated by alternative RNA splicing, endogenous IRES element and alternative translation initiation at the posttranscriptional level, may generates 4 isoforms with different function. All of these characteristics of Oct4 contribute to the complexity of its\' study. This work highlights the significance of differentiating the expression pattern and biological functions of Oct4 variants.
    Materials and methods
    Acknowledgments
    Introduction Umbilical cord blood transplantation (UCBT) holds great promise with apparent clinical advantages, but the transplant success rate remains much poorer than peripheral blood stem cell (PBSC) or bone marrow stem cell sources. This is due to the scarcity of stem BMN-673 manufacturer in each unit, thus ex vivo expansion of UBC continues to be an area of active research (Koestenbauer et al., 2009). Nonetheless, human UCB stem cells are useful for patients without matched related or unrelated donors, because an estimated 40%–80% of patients will not be able to find an acceptable adult stem cell donor for stem cell transplantation (Ballen et al., 2007; Barker et al., 2003; Brunstein et al., 2007; Misawa et al., 2006; Rocha et al., 2009). Human UCB offers practical advantages as an alternative source of bone marrow stem cell or PBSC, which include (1) the relative ease of procurement (ability to store fully tested and HLA-typed UCB available for immediate use); (2) the absence of risk to the mother and the donors; (3) the reduced likelihood of transmitting infections; (4) immaturity of immune cells, thus reduced risk of GVHD; (5) less stringent criteria for HLA matching for donor–recipient selection (with the potential of finding donors for minority populations); (6) absence of donor attrition (Chao et al., 2004); and (7) availability: UCB banks have been established for related and unrelated UCB transplantation with more than 100,000units being available based on published data (Barker et al., 2002; Gluckman et al., 2001; Kernan et al., 1993; Rocha et al., 2000). BMN-673 manufacturer Thus agents that can facilitate human UCB hematopoietic stem cell (HSC) and hematopoietic progenitor cell (HPC) expansion are highly desirable. The cytokine thrombopoietin (TPO) plays a crucial role in thrombopoiesis, in the regulation of HSCs, and in the proliferation of primitive HPCs. Both murine and human HSCs are highly enriched in cells expressing the TPO receptor c-Mpl (Solar et al., 1998; Yoshihara et al., 2007). Administration of TPO to myelosuppressed animals not only significantly alleviates thrombocytopenia, but also accelerates multiple lineage recovery (Akahori et al., 1996; Farese et al., 1996; Grossmann et al., 1996a, 1996b; Kaushansky et al., 1996; Neelis et al., 1997), promotes the reconstitution of multiple-lineage immature progenitors/precursors in bone marrow and spleen (Farese et al., 1996; Grossmann et al., 1996a; Kaushansky et al., 1996; Neelis et al., 1997), and augments the responses to GM-CSF and G-CSF (Farese et al., 1996; Grossmann et al., 1996a; Neelis et al., 1997). In vitro, TPO acts alone and most effectively in synergy with other early cytokines to promote survival and proliferation of HSCs and HPCs, and supports their expansion and differentiation into multiple-lineage colony-forming progenitors (Borge et al., 1997; Kobayashi et al., 1996; Ku et al., 1996; Luens et al., 1998; Ramsfjell et al., 1997; Petzer et al., 1996; Sitnicka et al., 1996; Young et al., 1996). TPO is also known to be critical for the replenishment of HSCs after bone marrow transplantation (Fox et al., 2002; Qian et al., 2007). These observations established the crucial roles of TPO receptor (c-Mpl) signaling on not only megakaryocytopoiesis, but also early hematopoiesis including regulation of HSCs.