MicroRNA expression profiling of elongated cloned and in vitro-fertilized bovine embryos

The objective of this study was to identify microRNAs (miRNAs) expressed in bovine (Bos Taurus) cloned embryos at Day 17 of development (Day 0=day of nucleus transfer or in vitro fertilization) during elongation. Day 7 bovine expanded blastocysts produced by hand made cloning (HMC) or in vitro fertilization were bulk-transferred to synchronized recipient cattle (48 HMC embryos to 10 recipients and 28 in vitro-produced embryos to four recipients). Elongated embryos were retrieved at Day 17; miRNAs were isolated and subjected to microarray screening using custom composite slides spotted with human, mouse, and rat and in silico-predicted miRNAs. An initial profile of expressed miRNAs was determined in cloned embryos and somatic donor cells; this profile changed after somatic cell nucleus transfer, identifying differentially expressed miRNAs between cloned and in vitro-produced bovine embryos. Furthermore, microarray data were validated using a miRNA-specific quantitative reverse transcription-polymerase chain reaction (qRT-PCR) approach (miR-Q). There was an 83% correlation (P=0.01) between microarray and qPCR data. Based on qRT-PCR, correct reprogramming of some miRNAs from the donor cells was confirmed in cloned bovine embryos, whereas other somatic miRNAs were not appropriately reprogrammed. Some of the miRNAs that were equally reprogrammed clustered on the same chromosomal location in the bovine genome. In conclusion, reprogramming of miRNAs seemed to occur in cloned bovine embryos. This could have profound implications for elucidating nuclear reprogramming in somatic cloning, as well as for the role of miRNAs in preimplantation mammalian development.