Structural and signalling molecules come together at tight junctions.

Tight junctions (TJs) have been suggested to act both as barriers and fences, but lack of information on the constituents of TJ strands has hampered the direct assessment of these functions. Over the past year, our understanding of the molecular architecture of TJ strands has increased markedly and we are ready to experimentally examine how TJs are involved in their dual functions.     

The 5' and 3' splice sites come together via a three dimensional diffusion mechanism.

We present evidence that the splice sites in mammalian pre-mRNAs are brought together via a three dimensional diffusion mechanism. We tested two mechanisms for splice site pairing: a lateral diffusion ('scanning') model and the currently favored three dimensional diffusion ('jumping') model. Two lines of evidence that distinguish between these two models are presented. The first utilized bipartite splicing substrates tethered by double-stranded RNA stems predicted to provide either a moderate or severe block to splice site pairing via a scanning mechanism. Splice site pairing via a jumping mechanism was expected to be unaffected or affected minimally. The second approach utilized a flexible poly(ethylene glycol) moiety within the intron. This insertion was predicted to reduce scanning efficiency but not the efficiency of a three dimensional diffusion mechanism. The best explanation for the data with the bipartite RNAs is that splice site pairing occurs through three dimensional diffusion. Kinetic analysis of the poly(ethylene glycol) containing substrate showed that neither the lag phase nor the initial rates of mRNA production and spliceosome assembly were affected by this insertion. Therefore, both experimental approaches supported the three dimensional diffusion model of splice site pairing.     

Restoring chromatin after replication: How new and old histone marks come together

In dividing cells genome stability and function rely on faithful transmission of both DNA sequence and its organization into chromatin. In the course of DNA replication chromatin undergoes transient genome-wide disruption followed by restoration on new DNA. This involves tight coordination of DNA replication and chromatin assembly processes in time and space. Dynamic recycling and de novo deposition of histones are fundamental for chromatin restoration. Histone post-translational modifications (PTMs) are thought to have a causal role in establishing distinct chromatin structures. Here we discuss PTMs present on new and parental histones and how they influence genome stability and restoration of epigenetically defined domains. Newly deposited histones must change their signature in the process of chromatin restoration, this may occur in a step-wise fashion involving replication-coupled processes and information from recycled parental histones.     

Bioethics for clinicians: 14. Ethics and genetics in medicine

Information about a patient''s inherited risk of disease has important ethical and legal implications in clinical practice. Because genetic information is by nature highly personal yet familial, issues of confidentiality arise. Counselling and informed consent before testing are important in view of the social and psychological risks that accompany testing, the complexity of information surrounding testing, and the fact that effective interventions are often not available. Follow-up counselling is also important to help patients integrate test results into their lives and the lives of their relatives. Genetic counselling should be provided by practitioners who have up-to-date knowledge of the genetics of and the tests available for specific diseases, are aware of the social and psychological risks associated with testing, and are able to provide appropriate clinical follow-up. Some physicians may elect to refer patients for genetic counselling and testing. However, it is inevitable that all physicians will be involved in long-term follow-up both by monitoring for disease and by supporting the integration of genetic information into patients'' lives.