Reprogramming somatic cells: pluripotency through gene induction and nuclear transfer
Bressan, Fabiana FernandesPerecin, FelipeSangalli, Juliano RodriguesMeirelles, Flávio Vieira
Background: The understanding of nuclear reprogramming pathways provides important contributions to applied and basic sciences such as the development of autologous cellular therapies for the treatment of numerous diseases, the improved efficiency of animal-based biotechnology or the generation of functional gametes in vitro. Strategies such as nuclear transfer and induced reprogramming have been used to induce somatic cells into an embryonic-like pluripotent state. Both techniques have been routinely performed worldwide, and live offspring have been successfully derived from them, resulting in a proof of efficacy of both techniques. Detailed studies on cellular and molecular mechanisms that mediate reprogramming, however, still require further investigation to develop practical applications in veterinary and human medicine. Review: Studies on cell reprogramming, differentiation and proliferation have revealed that a core of transcription factors, as for example, OCT4, SOX2 and NANOG, act together promoting cell commitment or pluripotency. Mechanisms of induced reprogramming by pluripotency-related transcription factors forced expression or nuclear transfer seems to be mediated by the same pathways observed in fertilization, eliciting nuclear remodeling and modulating gene expression. However, abnormal chromatin conformation, often leading to disrupted imprinting and atypical gene expression patterns are frequently observed on in vitro reprogramming. Strategies used to facilitate nuclear remodeling, such as chromatin modifying agents, as for example, histone deacetilases inhibitors or DNA methyltransferases; or chemicals responsible for the inhibition of development related pathways, as for example, MEK and GSK3 inhibitors, when used in the in vitro culture of cells or embryos, have proved to favors transcriptional regulation and improve reprogramming. Such alternatives are highly prone to enable the routine use of in vitro reprogramming in animal production and medical sciences, for example, by promoting the generation of functional male and female functional gametes capable of producing viable offspring. Thus, the properties, deficiencies and implications of induced reprogramming and nuclear transfer techniques in somatic cells were discussed in this review, as well as its probable outcomes. Conclusions: The combination of both reprogramming techniques - induced reprogramming and nuclear transfer, may be essential to clarify the mechanisms of gene expression that are responsible for induced pluripotency. As discussed here, the mechanisms responsible for triggering the pluripotency status of a somatic cell are probably closely related to the epigenetic changes and gene expression profiles present in early development following fertilization. We report here that the nuclear transfer of SOX2 expressing donor cells resulted in similar rates of embryo production when compared to control cells. A better understanding of the contribution of each reprogramming factor used in induced reprogramming may result in the establishment of strategies aiming to enhance in vitro reprogramming performance. Such knowledge will contribute to in vitro animal production by increasing the cloning efficiency and regenerative medicine through the derivation and adequate culture of reprogrammed embryonic stem cells.
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