Unfaithful Maintenance of Methylation Imprints Due to Loss of Maternal Nuclear Dnmt1 during Somatic Cell Nuclear Transfer

The low success rate of somatic cell nuclear transfer (SCNT) in mammalian cloning is largely due to imprinting problems. However, little is known about the mechanisms of reprogramming imprinted genes during SCNT. Parental origin-specific DNA methylation regulates the monoallelic expression of imprinted genes. In natural fertilization, methylation imprints are established in the parental germline and maintained throughout embryonic development. However, it is unclear whether methylation imprints are protected from global changes of DNA methylation in cloned preimplantation embryos. Here, we demonstrate that cloned porcine preimplantation embryos exhibit demethylation at differentially methylated regions (DMRs) of imprinted genes; in particular, demethylation occurs during the first two cell cycles. By RNAi-mediated knockdown, we found that Dnmt1 is required for the maintenance of methylation imprints in porcine preimplantation embryos. However, no clear signals were detected in the nuclei of oocytes and preimplantation embryos by immunofluorescence. Thus, Dnmt1 is present at very low levels in the nuclei of porcine oocytes and preimplantation embryos and maintains methylation imprints. We further showed that methylation imprints were rescued in nonenucleated metaphase II (MII) oocytes. Our results indicate that loss of Dnmt1 in the maternal nucleus during SCNT significantly contributes to the unfaithful maintenance of methylation imprints in cloned embryos

A real-time optimisation system for automation of furrow irrigation

An automated real-time optimisation system for furrow irrigation was developed and tested in this study. The system estimates the soil infiltration characteristics in real time and utilises the data to control the same irrigation event to give optimum performance for the current soil conditions. The main components of the system are as follows: the sensing of flow rate and a single advance time to a point approximately midway down the field, a system for scaling the soil infiltration characteristic and a hydraulic simulation program based on the full hydrodynamic model. A modem is attached to a microcomputer enabling it to receive signals from the flow meter and advance sensor via a radio telemetry system. Sample data from a furrow-irrigated commercial cotton property are used to demonstrate how the system works. The results demonstrate that improvements in on-farm water use efficiency and labour savings are potentially achievable through the use of the system