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de Caestecker and Macara study apical sorting of proteins with varying cytoplasmic tail length in epithelial cells. They propose that a size filter at the Golgi facilitates apical sorting of proteins with small cytoplasmic domains.

The Par polarity proteins are involved in regulating asymmetric division in stem cells in the fly. Macara and colleagues identify a PAR3 homologue that is expressed in multipotent stem cells in terminal end buds of the murine mammary gland, and is necessary for stem cell maintenance through its effect on Lkb1 kinase activity.

The exocyst delivers basolateral proteins from the secretory pathway to the plasma membrane of epithelial cells close to tight junctions. Here the authors show that Par3 acts as a docking site for the exocyst to regulate polarized delivery of basolateral proteins and this is essential to prevent apoptosis and promote mammary cell survival.

Fort et al. implicate apoptosis and an epithelial-to-mesenchymal transition in the cardiomyocyte conversion of human stem cells. Nucleotides released from dying cells act through P2Y2 receptors on surviving cells to license WNT-dependent mesoderm specification.

Exocyst complex tethers vesicles to plasma membranes, but assembly mechanisms remain unclear. Here, the authors use Cas9 gene editing to tag exocyst components in epithelial cells, and find that exocyst subcomplexes are recruited to membranes independently, but are both needed for vesicle fusion.

Using a multipurpose, single-cell CRISPR platform, we demonstrate precise timing of tissue-specific cell expansion during mouse embryonic development, unconventional developmental relationships between cell types, new epithelial progenitor states and insights into precancer initiation by leveraging genetic histories.

When DNA interstrand cross-links damage occurs, it causes disruption of replication and transcription. Here the authors identify FAM120B/SAN1, a 5′ exonuclease involved in the repair process of Interstrand Crosslinks independently of the Fanconi Anemia pathway.

Translation of localized mRNAs is an important mechanism for controlling spatially discrete cellular processes. The polarity protein Par-3 is locally translated in axons in response to factors such as NGF and netrin-1, and this increased expression is necessary for factor-stimulated axonal outgrowth.

The epithelial polarity programme (EPP) is organized in response to extracellular cues and executed through the establishment of an apical–basal axis, intercellular junctions, epithelial-specific cytoskeletal rearrangements and a polarized trafficking machinery. Recent studies have provided insights into the interactions of the EPP with the polarized trafficking machinery and how they regulate epithelial polarization and depolarization.

This paper reports the first crystal and electron microscopy structure of an individual septin and a heteromeric complex as well as linear septin filaments. The structure reveals that the G domain, which is conserved amongst all septins, serves as a universal building block for formation of a polymer. This domain interacts with other septins via conserved residues.

The small GTPase Cdc42 is an important regulator of cell polarity that localizes to both the plasma membrane and to the Golgi. Baschieri et al.show that the Golgi pool of Cdc42 is regulated by GM130–RasGRF, and that deregulation of this pathway is associated with loss of polarity and tumorigenesis.

Defects in non-canonical Wnt/planar cell polarity signalling have recently been linked to breast cancer aggressiveness. Puvirajesinghe et al. identify VANGL2, p62/SQSTM1 and JNK as important players in this pathway which may be amenable to therapeutic intervention in breast cancer.

The most interesting discoveries are often those that couple distinct fields of science in unexpected ways. The marriage of the nuclear pore complex to the kinetochore and spindle checkpoint regulation is a recent example, raising the question of why such divergent processes as mitosis and nuclear transport use common proteins.

RNA localization is important in diverse biological process including establishment of polarity. This study has focused on migrating fibroblasts that polarize to form a leading edge and tail, in a process that involves assymetric distribution of RNAs. On a genome-wide scale RNAs that are localized to cell protrusions are identified. Through their 3' UTRs, these transcripts are anchored in granules concentrated at the plus end of microtubules and associate with the APC tumour suppressor.

α-N-methylation is an unusual post-translational modification in which the amino-terminal residues of proteins are methylated. One example is the Ran guanine nucleotide-exchange factor, RCC1, which requires methylation for its association with chromatin. These authors describe the first α-N-methyltransferase, named N-terminal RCC1 methyltransferase (NRMT). They identify the NRMT recognition sequence and several new methylation targets, and demonstrate the importance of α-N-methylation for normal bipolar spindle formation and chromosome segregation.