Unfortunately, in epigenetics, as with all other research areas, the more the discoveries, the more confusing the field seems to get. Regarding the histone code, until recently it was clear that some histone marks activate neighboring genes while other epigenetic marks switch off selected genes. In theory, some epigenetic changes ensure that chromatin-DNA-protein complexes stay compact, whereas some loosen chromatin.
Recently, a research team from Barcelona led by Roderic Guigó found out that this rule does not apply to certain genes, at least not in flies and worms. Researchers analyzed data from the modENCODE project that systematically collects data from genomes of model organisms, e.g. roundworms and fruit flies. Guigó and colleagues demonstrated that the regulation of such genes that are needed during the development of fly or worm seems independent of the histone code. The genes are turned on or off by the action of transcription factors, without the involvement histones that typically demonstrate a typical methylation pattern of active/inactive chromatin. This epigenetic labeling pattern may regulate cells even in cases when certain genes should remain active all times.
Source: http://www.newsletter-epigenetik.de/Read more