Volume 9 Issue 1, January 2007

The nucleosome surface is decorated with an array of enzyme-catalysed modifications on histone tails. These modifications have well-defined roles in a variety of ongoing chromatin functions, often by acting as receptors for non-histone proteins, but their longer-term effects are less clear. Here, an attempt is made to define how histone modifications operate as part of a predictive and heritable epigenetic code that specifies patterns of gene expression through differentiation and development.

New studies reveal the dynamic accumulation of phosphatidylinositol (3,4,5) trisphosphate (PtdIns(3,4,5)P₃) at the leading edge of primary neutrophils during chemotaxis. They also demonstrate that SHIP1, rather than phosphatase and tensin homologue (PTEN), is responsible for the degradation and localization of this lipid in neutrophils and shed light on the role of PtdIns(3,4,5)P₃ in directional sensing.

Bone morphogenetic proteins (BMPs) shape vertebrate limbs and define digits by inducing programmed cell death in interdigital tissues. Recent findings show that Drosophila legs are also sculpted by programmed cell death. In this case, rather than the absolute activity of BMP, it is the sharp discontinuity of BMP signalling that is required for forming the leg joint.

In eukaryotes, condensing chromosomal DNA into heterochromatin is important for gene silencing and proper chromosome segregation. A recent study suggests a function for heterochromatin in protecting highly repeated genes and satellite DNA against excision caused by recombination or by joining of free DNA ends following DNA damage.

Each round of DNA replication results in the erosion of telomeres, the ends of linear chromosomes. Telomerase counteracts telomere shortening by synthesizing new DNA sequences in a time period restricted to late S a d G2 cell-cycle phases, even though the enzyme is active throughout the cell cycle. A recent study directly implicates cyclin dependent kinase (Cdk1) in the regulation of telomere elongation during the cell cycle.