Progress

Respiratory chain subunits are made up of proteins encoded by nuclear and mitochondrial DNA, which assemble to form functional enzymes. New findings reveal that the mitochondrial translation of Cox1, the core component of cytochromecoxidase, is directly coupled to the assembly of this respiratory complex.

Mitophagy is the selective elimination of mitochondria through autophagy. Recent studies have uncovered the molecular mechanisms mediating mitophagy in yeast and mammalian cells and have revealed that the dysregulation of one of these mechanisms — the PINK1–parkin-mediated signalling pathway — may contribute to Parkinson's disease.

Transport protein particle (TRAPP; also known as trafficking protein particle) complexes activate the GTPase Ypt1 or RAB1 to regulate membrane traffic in yeast and mammals, respectively. Two different TRAPP complexes tether coated vesicles during endoplasmic reticulum–Golgi and intra-Golgi traffic, respectively, and a third complex functions in autophagy. The TRAPP complexes thereby connect GTPase activation to unique membrane-tethering events.

In mammalian cells, several proteins that are not part of the core replication machinery promote the efficient restart of stalled replication forks, which suggests that fork restart pathways exist. Different models of restart can be envisaged, which involve DNA helicases, nucleases, homologous recombination factors and DNA double-strand breaks.

Several human neurological and neuromuscular diseases are caused by the expansion of repetitive DNA tracts. Understanding the DNA metabolic processes responsible for the expansion (or lengthening) and contraction (or shortening) of DNA repeats might open new therapeutic avenues for the treatment of these diseases.

The Bicoid (BCD) morphogen gradient was thought to be formed by diffusion of the protein away from the anterior pole of theDrosophila melanogasterembryo. A new study shows that a bcd mRNA gradient prefigures the protein gradient and proposes a model that combines active mRNA transport with local BCD translation.

Natural antisense transcripts are frequently functional and are involved in regulating gene expression. The authors summarize the proposed actions of antisense transcript into four models, each corresponding to a putative regulatory mechanism for a subset of antisense transcripts.

An endogenous small interfering RNA (endo-siRNA) pathway had only previously been characterized in worms. The recent discovery of diverse intramolecular and intermolecular substrates that generate endo-siRNAs in flies and mice raise many questions regarding the biogenesis and function of small regulatory RNAs in animals.

Membrane nanotubes are thin extensions of the plasma membrane that connect cells transiently and might facilitate intercellular communication. Recent studies have revealed considerable heterogeneity in their structure, formation, mode of cargo transport and functional properties, depending on the cell types involved.