Passagem celular, sexo e transcrição X-específica interferem no desenvolvimento embrionário e fetal de bovinos produzidos por transferência nuclear / Celular passage, sex and X-specific transcription interfere in bovine nuclear transfer embryo and fetal development

AUTOR(ES)
DATA DE PUBLICAÇÃO

2007

RESUMO

Cells cultured for long-term periods accumulate genetic and epigenetic modifications that result in improper nuclear reprogramming of somatic cell nuclear transfer (SCNT) embryos. Furthermore, the sex may be a limiting factor in blastocysts production and in post-implantation developmental competence. Therefore, the objective of this study was to determine the effect of the passage number for SCNT, and to evaluate the effect of sex on in vitro development and on post-implantational competence of these embryos. Oocytes obtained from slaughtered cows were enucleated and reconstructed by TNCS from an adult animal at 18 hours of in vitro maturation. After fusion (two 2.25 kv/cm DC pulses for 65 µsec) and chemical activation (5.0 µM ionomycin for 5 min followed by 2.0 mM 6-DMAP for 3 hours), the reconstructed zygotes were cultured in CR2 on a granulosa cell monolayer at 38.8ºC in a humidified atmosphere of 5% CO2 in air for 7 days. Data were analyzed using Chi Square analysis. Reconstructed embryos with cells on late passages showed lower rates for cleavage, 8 cells embryos and blastocyst formation (p <0.05). Reconstructed embryos with cells on early passages showed higher competence to blastocyst formation (16% versus 14% - intermediate and 7% - late; p <0.05). Although reconstructed embryos with cells on late passages showed similar results for pregnancy on day 30 (35% versus 27% - early and 26% - intermediate), they were not competent to develop to term. Calving rates and perinatal survival (PNS) were similar when comparing early and intermediate passages (34% vs 25% and 50% vs 57%, respectively). Regarding sex, although cleavage rates were higher for female embryos (78% vs 74%; p <0.05), male embryos were more competent for blastocyst formation (16% vs 14.5%; p <0.05). The pregnancy rate, development to term and PNS were similar between gender, however, female embryos showed higher rates of abortion between day 90 and 120. In conclusion, these results indicate that long-term culture of donor cells decrease blastocyst formation and increase the chances of failure during pregnancy. Futhermore, cloned male embryos were more competent to form a blastocyst and had lower rates of abortion.

ASSUNTO(S)

bovino expressão gênica transferência nuclear cromossomo x passagem celular sexo gene expression x chomosome bovine celular passage sex nuclear transfer

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