Maternal siRNAs as regulators of parental genome imbalance and gene expression in endosperm of Arabidopsis seeds

Seed size is important to crop domestication and natural selection and is affected by the balance of maternal and paternal genomes in endosperm. Endosperm, like placenta in mammals, provides reserves to the developing embryo. Interploidy crosses disrupt the genome balance in endosperm and alter seed size. Specifically, paternal-excess crosses (2 × 4) delay endosperm cellularization (EC) and produce larger seeds, whereas maternal-excess crosses (4 × 2) promote precocious EC and produce smaller seeds. The mechanisms for responding to the parental genome dosage imbalance and for gene expression changes in endosperm are unknown. In plants, RNA polymerase IV (PolIV or p4) encoded by NRPD1a is required for biogenesis of a major class of 24-nt small interfering RNAs (also known as p4-siRNAs), which are predominately expressed in developing endosperm. Here we show that p4-siRNA accumulation depends on the maternal genome dosage, and maternal p4-siRNAs target transposable elements (TEs) and TE-associated genes (TAGs) in seeds. The p4-siRNAs correlate negatively with expression levels of AGAMOUS-LIKE (AGL) genes in endosperm of interploidy crosses. Moreover, disruption of maternal NRPD1a expression is associated with p4-siRNA reduction and AGL up-regulation in endosperm of reciprocal crosses. This is unique genetic evidence for maternal siRNAs in response to parental genome imbalance and in control of transposons and gene expression during endosperm development.     

Genomic landscape of human allele-specific DNA methylation

DNA methylation mediates imprinted gene expression by passing an epigenomic state across generations and differentially marking specific regulatory regions on maternal and paternal alleles. Imprinting has been tied to the evolution of the placenta in mammals and defects of imprinting have been associated with human diseases. Although recent advances in genome sequencing have revolutionized the study of DNA methylation, existing methylome data remain largely untapped in the study of imprinting. We present a statistical model to describe allele-specific methylation (ASM) in data from high-throughput short-read bisulfite sequencing. Simulation results indicate technical specifications of existing methylome data, such as read length and coverage, are sufficient for full-genome ASM profiling based on our model. We used our model to analyze methylomes for a diverse set of human cell types, including cultured and uncultured differentiated cells, embryonic stem cells and induced pluripotent stem cells. Regions of ASM identified most consistently across methylomes are tightly connected with known imprinted genes and precisely delineate the boundaries of several known imprinting control regions. Predicted regions of ASM common to multiple cell types frequently mark noncoding RNA promoters and represent promising starting points for targeted validation. More generally, our model provides the analytical complement to cutting-edge experimental technologies for surveying ASM in specific cell types and across species.     

Influence of middle-distance running on muscular micro RNAs

A specific subset of micro RNAs (miRs), including miR-133 and miR-206, is specifically expressed in muscle tissue, so that they are currently defined as muscular miRs (myomiRs). To further elucidate the role of myomiRs in muscle biology, we measured miR-133a and miR-206 in plasma of 28 middle-age recreational athletes. The study population consisted of 28 middle aged, recreation athletes (11 women and 17 men; mean age, 46?years) who completed a 21.1?km, half-marathon. The plasma concentration of miR-133a and miR-206, the serum concentration of creatine kinase (CK) and high-sensitivity (HS) cardiac troponin T (cTnT), as well as capillary lactate, were measured before and immediately after the run. The median serum concentration of total CK (257 versus 175?U/L; p?p??4; p??4; p?=?.001) were considerably increased immediately after the half-marathon run. In multivariate analysis only post-exercise capillary lactate was found to be independently associated with running time. A significant and independent correlation was observed between plasma variations of the two miRs, but not with other physiological or laboratory parameters. The results of this study suggest that the biological significance of miR-133a and 206 variation after middle-distance running parallels but not overlaps the release of biomarkers of nonspecific tissue damage. Enhanced plasma values of these myomiRs may hence reflect a physiological response to high-intensity and/or prolonged exercise rather than tissue injury.