Forty Years of Clathrin‐coated Vesicles

The purification of coated vesicles and the discovery of clathrin by Barbara Pearse in 1975 was a landmark in cell biology. Over the past 40 years, work from many labs has uncovered the molecular details of clathrin and its associated proteins, including how they assemble into a coated vesicle and how they select cargo. Unexpected connections have been found with signalling, development, neuronal transmission, infection, immunity and genetic disorders. But there are still a number of unanswered questions, including how clathrin‐mediated trafficking is regulated and how the machinery evolved.      

Identifying qualitative effects of different grazing types on below‐ground communities and function in a long‐term field experiment

Herbivory is an important modulator of plant biodiversity and productivity in grasslands, but our understanding of herbivore‐induced changes on below‐ground processes and communities is limited. Using a long‐term (17 years) experimental site, we evaluated impacts of rabbit and invertebrate grazers on some soil functions involved in carbon cycling, microbial diversity, structure and functional composition. Both rabbit and invertebrate grazing impacted soil functions and microbial community structure. All functional community measures (functions, biogeochemical cycling genes, network association between different taxa) were more strongly affected by invertebrate grazers than rabbits. Furthermore, our results suggest that exclusion of invertebrate grazers decreases both microbial biomass and abundance of genes associated with key biogeochemical cycles, and could thus have long‐term consequences for ecosystem functions. The mechanism behind these impacts are likely to be driven by both direct effects of grazing altering the pattern of nutrient inputs and by indirect effects through changes in plant species composition. However, we could not entirely discount that the pesticide used to exclude invertebrates may have affected some microbial community measures. Nevertheless, our work illustrates that human activity that affects grazing intensity may affect ecosystem functioning and sustainability, as regulated by multi‐trophic interactions between above‐ and below‐ground communities.     

Many ways to build an actin filament

Cells rely on extensive networks of protein fibres to help maintain their proper form and function. For species ranging from bacteria to humans, this 'cytoskeleton' is integrally involved in diverse processes including movement, DNA segregation, cell division and transport of molecular cargoes. The most abundant cytoskeletal filament-forming protein, F-actin, is remarkably well conserved across eukaryotic species. From yeast to human - an evolutionary distance of over one billion years - only about 10% of residues in actin have changed and the filament structure has been highly conserved. Surprisingly, recent structural data show this to be not the case for filamentous bacterial actins, which exhibit highly divergent helical symmetries in conjunction with structural plasticity or polymorphism, and dynamic properties that may make them uniquely suited for the specific cellular processes in which they participate. Bacterial actin filaments often organize themselves into complex structures within the prokaryotic cell, driven by molecular crowding and cation association, to form bundles (ParM) or interwoven sheets (MreB). The formation of supramolecular structures is essential for bacterial cytoskeleton function. We discuss the underlying physical principles that lead to complex structure formation and the implications these have on the physiological functions of cytoskeletal proteins.     

Enteropathogenic and enterohaemorrhagic Escherichia coli: even more subversive elements

The human pathogens enteropathogenic and enterohemorrhagic Escherichia coli (EPEC and EHEC) share a unique mechanism of colonization that results from the concerted action of effector proteins translocated into the host cell by a type III secretion system (T3SS). EPEC and EHEC not only induce characteristic attaching and effacing (A/E) lesions, but also subvert multiple host cell signalling pathways during infection. Our understanding of the mechanisms by which A/E pathogens hijack host cell signalling has advanced dramatically in recent months with the identification of novel activities for many effectors. In addition to further characterization of established effectors (Tir, EspH and Map), new effectors have emerged as important mediators of virulence through activities such as mimicry of Rho guanine nucleotide exchange factors (Map and EspM), inhibition of apoptosis (NleH and NleD), interference with inflammatory signalling pathways (NleB, NleC, NleE and NleH) and phagocytosis (EspF, EspH and EspJ). The findings have highlighted the multifunctional nature of the effectors and their ability to participate in redundant, synergistic or antagonistic relationships, acting in a co-ordinated spatial and temporal manner on different host organelles and cellular pathways during infection.     

The sound of silence: ionic mechanisms encoding sound termination

Offset responses upon termination of a stimulus are crucial for perceptual grouping and gap detection. These gaps are key features of vocal communication, but an ionic mechanism capable of generating fast offsets from auditory stimuli has proven elusive. Offset firing arises in the brainstem superior paraolivary nucleus (SPN), which receives powerful inhibition during sound and converts this into precise action potential (AP) firing upon sound termination. Whole-cell patch recording in?vitro showed that offset firing was triggered by IPSPs rather than EPSPs. We show that AP firing can emerge from inhibition through integration of large IPSPs, driven by an extremely negative chloride reversal potential (E(Cl)), combined with a large hyperpolarization-activated nonspecific cationic current (I(H)), with a secondary contribution from a T-type calcium conductance (I(TCa)). On activation by the IPSP, I(H) potently accelerates the membrane time constant, so when the sound ceases, a rapid repolarization triggers multiple offset APs that match onset timing accuracy.     

Specificity, location and function of βTrCP isoforms and their splice variants

SCF^βTrCP is the ubiquitin ligase for a wide variety of substrates and functions in many cellular processes. βTrCP, the substrate binding factor of the SCF complex, has two isoforms, produced from different genes, and several splice variants. Despite a certain level of redundancy, knock-out studies show different phenotypes indicating different preferential substrates for the two isoforms. However, until now functional differences between βTrCP1 and 2 were not studied at the endogenous protein level. We generated isoform-specific antibodies against βTrCP to characterise endogenous βTrCP isoforms and splice variants. We show that endogenous βTrCP1 and 2 localise to both nucleus and cytosol. Interestingly, we find that one splice variant of βTrCP2 localises exclusively to the nucleus and another only to the cytosol. In addition, we show that the substrate binding domain of βTrCP is the dominant localisation determinant.