Dnmt1 expression in pre- and postimplantation embryogenesis and the maintenance of IAP silencing

The methylation of intracisternal A-type particle (IAP) sequences is maintained during mouse embryogenesis. Methylation suppresses IAP expression and the potential for mutagenesis by retrotransposition, but it is not clear how methylation of these elements is maintained during the embryonic stages when the bulk of the genome is being demethylated. It has been suggested that the high levels of DNA methyltransferase-1 (Dnmt1) present during cleavage could be important for keeping IAPs methylated. To test this hypothesis, we combined mutant alleles of Dnmt1 with an agouti allele (A(iapy)), which provided a coat color readout for the methylation status of the IAP insertion in the agouti locus. We found that reduction in Dnmt1 levels directly impacted methylation at this locus, leading to stable transcriptional activation of the agouti gene in the adult. Specifically, the short maternal Dnmt1 protein was important in maintaining methylation at the A(iapy) locus in cleavage embryos, whereas the longer Dnmt1 isoform found in somatic cells was important in maintaining IAP methylation during the postimplantation stage. These results underscore the importance of maintaining proper maintenance of methylation patterns during gestation and suggest that interference with this process may stably affect gene expression patterns in the adult and may have profound phenotypic consequences

Asian Childhoods: exploring the lifeworlds of students in contemporary Hong Kong

In this article, the authors discuss the findings of two surveys that were conducted with 10-year-old primary students and their parents in Hong Kong. They sought to gather empirical data about how the students spend their time in out-of-school contexts in order to interrogate the view that Asian students often spend much of their time studying, with little leisure time. The authors were concerned that there was an absence of empirical data on this topic. Increasingly, there is a recognition that Asian students perform well in high-stakes international tests, and a widely held view is that this is because they dedicate so much time to intensive academic study in contrast to their ‘Western’ counterparts. The social and cultural capital derived from doing well in school systems is an established feature of many global contexts. In the competitive environment that characterises education in Hong Kong, progression through the system is based solely on examination scores, and justified on the basis that this is both equitable and allows the best students to thrive. Tutorial schools that train attendees in the art of testing are multimillion-dollar industries – but who are the clients? In this article, the authors reveal that at 10 years of age, the out-of-school lives of the students surveyed contain many and varied activities. They attend school and, in out-of-school contexts, complete homework, participate in activities that both incorporate new media (for example, television and computers) and others (for example, indoor and outdoor play), and do not