RESUMO
In this study, we analyzed the effects of the cloned embryo aggregation on in vitro embryo development and embryo quality by measuring blastocyst diameter and cell number, DNA fragmentation levels and the expression of genes associated with pluripotency, apoptosis, trophoblast and DNA methylation in the porcine. Zona-free reconstructed cloned embryos were cultured in the well of the well system, placing one (1x non aggregated group) or three (3x group) embryos per microwell. Our results showed that aggregation of three embryos increased blastocyst formation rate and blastocyst diameter of cloned pig embryos. DNA fragmentation levels in 3x aggregated cloned blastocysts were significantly decreased compared to 1x blastocysts. Levels of Oct4, Klf4, Igf2, Bax and Dnmt 1 transcripts were significantly higher in aggregated embryos, whereas Nanog levels were not affected. Transcripts of Cdx2 and Bcl-xl were essentially non-detectable. Our study suggests that embryo aggregation in the porcine may be beneficial for cloned embryo development and embryo quality, through a reduction in apoptotic levels and an improvement in cell reprogramming.
Assuntos
Clonagem de Organismos , Embrião de Mamíferos , Desenvolvimento Embrionário , Animais , Apoptose , Blastocisto/citologia , Blastocisto/metabolismo , Reprogramação Celular/genética , Fragmentação do DNA , Técnicas de Cultura Embrionária , Transferência Embrionária , Expressão Gênica , Perfilação da Expressão Gênica , Suínos , Fatores de Transcrição/genética , Fatores de Transcrição/metabolismoRESUMO
BACKGROUND: Microcell-mediated chromosome transfer (MMCT) was developed to introduce a low number of chromosomes into a host cell. We have designed a novel technique combining part of MMCT with somatic cell nuclear transfer, which consists of injecting a somatic micronucleus into an enucleated oocyte, and inducing its cellular machinery to replicate such micronucleus. It would allow the isolation and manipulation of a single or a low number of somatic chromosomes. METHODS: Micronuclei from adult bovine fibroblasts were produced by incubation in 0.05 µg/ml demecolcine for 46 h followed by 2 mg/ml mitomycin for 2 h. Cells were finally treated with 10 µg/ml cytochalasin B for 1 h. In vitro matured bovine oocytes were mechanically enucleated and intracytoplasmatically injected with one somatic micronucleus, which had been previously exposed [Micronucleus- injected (+)] or not [Micronucleus- injected (-)] to a transgene (50 ng/µl pCX-EGFP) during 5 min. Enucleated oocytes [Enucleated (+)] and parthenogenetic [Parthenogenetic (+)] controls were injected into the cytoplasm with less than 10 pl of PVP containing 50 ng/µl pCX-EGFP. A non-injected parthenogenetic control [Parthenogenetic (-)] was also included. Two hours after injection, oocytes and reconstituted embryos were activated by incubation in 5 µM ionomycin for 4 min + 1.9 mM 6-DMAP for 3 h. Cleavage stage and egfp expression were evaluated. DNA replication was confirmed by DAPI staining. On day 2, Micronucleus- injected (-), Parthenogenetic (-) and in vitro fertilized (IVF) embryos were karyotyped. Differences among treatments were determined by Fisher's exact test (p≤0.05). RESULTS: All the experimental groups underwent the first cell divisions. Interestingly, a low number of Micronucleus-injected embryos showed egfp expression. DAPI staining confirmed replication of micronuclei in most of the evaluated embryos. Karyotype analysis revealed that all Micronucleus-injected embryos had fewer than 15 chromosomes per blastomere (from 1 to 13), while none of the IVF and Parthenogenetic controls showed less than 30 chromosomes per spread. CONCLUSIONS: We have developed a new method to replicate somatic micronuclei, by using the replication machinery of the oocyte. This could be a useful tool for making chromosome transfer, which could be previously targeted for transgenesis.