The temporal and spatial control of stem-cell divisions is tightly regulated to ensure proper development of the organism. This month sees two new instalments in our Article Series on Developmental Cell Biology (http://www.nature.com/nrm/series/devcellbiol) that shed light on the signalling cascades that regulate stem-cell proliferation and differentiation in worms and mammals.

On page 766, Edward T. Kipreos discusses the different cell-cycle control mechanisms that result in a defined number of somatic cells in the adult worm and allow continuous germ line proliferation throughout its life. Magdalena Götz and Wieland B. Huttner (page 777) dissect the proliferation and differentiation mechanisms of stem cells during the development of the central nervous system in mammals. Mechanisms that control apical–basal polarity and cell-cycle length are thought to be responsible for cell-fate changes and neurogenesis.

A research area that has progressed in leaps and bounds of late is the study of chromatin modifications at sites of DNA damage. Chromatin modifications are key regulators of transcription, but their role in DNA repair has become apparent only recently. On page 757, Haico van Attikum and Susan M. Gasser discuss how the phosphorylation of histone H2A promotes the accumulation of checkpoint and repair proteins to DNA double-strand breaks. Other chromatin modifications have also been implicated, but how they impact on the cellular response to DNA damage remains to be clarified.

Finally, as you might have gathered from the cover, Nature Reviews Molecular Cell Biology celebrates its fifth anniversary this month. We would like to thank all authors and referees, who, together with our readers, have made the past 5 years a resounding success.