Detección de RNAs circulares del gen Smaug1/SAMD4 en diferentes tejidos de ratón
The circular RNAs (circRNAs) are a new class of recently reported RNAs, and their functions are still an emerging issue. Its biogenesis has been described as a product of a process called back-splicing that occurs during the maturation of pre-mRNA6,7. In this process the donor site of the exon is li...
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| Formato: | Tesis de maestría acceptedVersion |
| Lenguaje: | Español |
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Facultad de Farmacia y Bioquímica
2019
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| Acceso en línea: | http://repositoriouba.sisbi.uba.ar/gsdl/cgi-bin/library.cgi?a=d&c=afamaster&cl=CL1&d=HWA_3170 http://repositoriouba.sisbi.uba.ar/gsdl/collect/afamaster/index/assoc/HWA_3170.dir/3170.PDF |
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| Sumario: | The circular RNAs (circRNAs) are a new class of recently reported RNAs, and their functions are still an emerging issue. Its biogenesis has been described as a product of a process called back-splicing that occurs during the maturation of pre-mRNA6,7. In this process the donor site of the exon is linked to the acceptor site thanks to a complementarity generated by the formation of intronic loops, thus generate a circular molecule that can be constituted only by exons (monoexonic, multi-exonic), only introns, or both4,17. It is also known that their structure gives them greater stability and makes them resistant to degradation by some RNases such as RNAse R, unlike linear RNAs.\nTo date, different functions of the circRNAs have been postulated as: competence of splicing against the gene from which are generated, sponges of miRNAs, regulators of methylation of CpG islands, or mediators in migration of pAKT to nucleus. Thus, circular RNAs are considered important post-transcriptional regulators, essentials for regulation of cell survival, and have been used as biomarkers in cancer4,10,11,12,18,19,20,21.\nThe greater accumulation of circRNAs has been reported in neural tissue, which agrees with the low cellular regeneration in that tissue, and with the greater stability against the degradation of circRNAs respect to linear RNAs. Its abundance in neural tissue has also led to relate them with development of different pathologies of the nervous system that are shown in older people.\nThe Smaug1 protein encoded by samd4 gene in mice and samd4a in humans is a translational repressor. This protein has been described in different organisms including Hommo Sapiens, Mus Musculus, Saccharomyces cerevisiae, and Drosophila Melanogaster. Initially described in Drosophila, the Smaug protein acts as regulator of the stability and translation of maternal mRNAs during embryonic development, interrupting the interaction between the factors of initiation of translation eIF4E and eIF4G52. In this way, Smaug captures target transcripts in repression complexes called S-foci. These silencing centers are organelles without membranes that behave as dynamic structures that self-assemble and contain mRNAs wich are not being translated, together with various proteins that regulate their translation, localization and degradation25,28,29,54.\nIn the mammalian genome there are 2 homologous genes called Smaug1 and Smaug2. Using mouse hippocampal neurons, in our laboratory we demonstrated that Smaug1 is located in synapse, regulating the synaptic plasticity. It was also shown that neuronal S-foci respond to synaptic stimuli 27,29,31,34. Subsequent to our findings, it has been shown that Smaug2 is involved on regulation of neurogenesis in mouse brain36.\nIn mammals Smaug1 and Smaug2 are expressed not only in CNS, but also in other tissues such: heart, bone, muscle and adipose tissue27,48,49. In our laboratory, we described the presence of two variants of splicing from Smaug1 in different human cell lines that arise from the alternative processing of exon III. It is important to note that the isoform of human Smaug1 lacking exon III shows RNA binding capacity, and a\nrepressor activity comparable to full-length human Smaug135. The homologue of Smaug1, Smaug2, is also present in the cell lines studied. Both, Smaug1 and Smaug2 form cytosolic bodies when are transfected into cell lines. Studies from another laboratory showed that in murine neural cortex cells, Smaug2 promotes neurogenesis by acting as translational repressor of nanos1 mRNA, a second RNA binding protein, capable of regulating translation and stability of transcripts36.\nAlthough Smaug1 and Smaug2 are more abundantly expressed in the brain, in mammals the Smaug mutants reported do not present phenotypes associated with the CNS. Recently, a samd4 mutation called "Supermodel" has been identified in mice, causing thinness and kyphosis associated with myopathy, and adipocyte defects. This point mutation generates a change of histidine for proline in the amino acid position 86 of the isoform1 from samd4, which in homozygosis generates mice resistant to the development of obesity induced by a high-fat diet. These metabolic defects in Supermodel mice were associated with modulation of target activities of the rapamycin1/mTORC1 (main regulator of metabolism) target complex mediated by Smaug1, evidenced by hypophosphorylation of the start translation factor 4E-BP1 and the ribosomal protein S6 in muscle and adipose tissues of homozygous mice48. Another research group analyzed a mutation of samd4 product of a transposon in homozygous mice that confers a phenotype associated with deficiency on development of skeleton, and reproduces the supermodel phenotype with a notable reduction of adipose tissue49.\nIt is suggested, then, that the post-transcriptional pathway mediated by Smaug1 is relevant not only for development of neurons, also for adipocyte development and during osteoblastogenesis.\nObesity is a disease with a high mortality rate worldwide. It is generated due to the large accumulation of triglycerides in adipocytes, generating hypertrophy and hyperplasia of adipose tissue, and is responsible for development Metabolic Syndrome (MS), branching into: central obesity, insulin resistance, non-alcoholic fatty liver, hypertension.\nIn this work, we identified the presence of Smaug1 circRNA (mmu_cir_0000529) in a model for the study of adipocyte differentiation and simultaneously analyzed the splicing of linear isoforms from Smaug1/Samd4. |
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