Directional cell migration requires the establishment and maintenance of long-term differences in structure and function between the front and back of a cell. Here, we show that the microtubule motor Kif1C contributes to persistent cell migration primarily through stabilization of an extended cell rear. Kif1C-mediated transport of α5β1-integrins is required for the proper maturation of trailing focal adhesions and resistance to tail retraction. Tail retraction precedes and induces changes in migration direction. Stabilization of cell tails through inhibition of myosin II activity suppresses the Kif1C depletion phenotype and results in longer-lived tails and higher directional stability of migrating cells. Taken together, these findings indicate that the maintenance of an extended, tense cell tail facilitates directional migration. We propose a rear drag mechanism for directional persistence of migration whereby the counterforce originating from a well-anchored tail serves to maintain directionality of the force-generating leading edge of the cell.

Households provide environments that encourage the formation of microbial communities, often as biofilms. Such biofilms constitute potential reservoirs for pathogens, particularly for immune-compromised individuals. One household environment that potentially accumulates microbial biofilms is that provided by vinyl shower curtains. Over time, vinyl shower curtains accumulate films, commonly referred to as "soap scum," which microscopy reveals are constituted of lush microbial biofilms. To determine the kinds of microbes that constitute shower curtain biofilms and thereby to identify potential opportunistic pathogens, we conducted an analysis of rRNA genes obtained by PCR from four vinyl shower curtains from different households. Each of the shower curtain communities was highly complex. No sequence was identical to one in the databases, and no identical sequences were encountered in the different communities. However, the sequences generally represented similar phylogenetic kinds of organisms. Particularly abundant sequences represented members of the ␣-group of proteobacteria, mainly Sphingomonas spp. and Methylobacterium spp. Both of these genera are known to include opportunistic pathogens, and several of the sequences obtained from the environmental DNA samples were closely related to known pathogens. Such organisms have also been linked to biofilm formation associated with water reservoirs and conduits. In addition, the study detected many other kinds of organisms at lower abundances. These results show that shower curtains are a potential source of opportunistic pathogens associated with biofilms. Frequent cleaning or disposal of shower curtains is indicated, particularly in households with immune-compromised individuals.

<p>Specialised cellular networks of oxidoreductases coordinate the dithiol/disulfide-exchange reactions that control metabolism, protein regulation, and redox homeostasis. For probes to be selective for redox enzymes and effector proteins (nM to µM concentrations), they must also be able to resist nonspecific triggering by the ca. 50 mM background of non-catalytic cellular monothiols. However, no such selective reduction-sensing systems have yet been established. Here, we used rational structural design to independently vary thermodynamic and kinetic aspects of disulfide stability, creating a series of unusual disulfide reduction trigger units designed for stability to monothiols. We integrated the motifs into modular series of fluorogenic probes that release and activate an arbitrary chemical cargo upon reduction, and compared their performance to that of the literature-known disulfides. The probes were comprehensively screened for biological stability and selectivity against a range of redox effector proteins and enzymes. This design process delivered the first disulfide probes with excellent stability to monothiols, yet high selectivity for the key redox-active protein effector, thioredoxin. We anticipate that further applications of these novel disulfide triggers will deliver unique probes targeting cellular thioredoxins. We also anticipate that further tuning following this design paradigm will deliver redox probes for other important dithiol-manifold redox proteins, that will be useful in revealing the hitherto hidden dynamics of endogenous cellular redox systems.</p>

Mitosis in animals starts with the disassembly of the nuclear pore complexes and the breakdown of the nuclear envelope. In contrast to many fungi, the corn smut fungus Ustilago maydis also removes the nuclear envelope. Here, we report on the dynamic behavior of the nucleoporins Nup214, Pom152, Nup133, and Nup107 in this "open" fungal mitosis. In prophase, the nuclear pore complexes disassembled and Nup214 and Pom152 dispersed in the cytoplasm and in the endoplasmic reticulum, respectively. Nup107 and Nup133 initially spread throughout the cytoplasm, but in metaphase and early anaphase occurred on the chromosomes. In anaphase, the Nup107-subcomplex redistributed to the edge of the chromosome masses, where the new envelope was reconstituted. Subsequently, Nup214 and Pom152 are recruited to the nuclear pores and protein import starts. Recruitment of nucleoporins and protein import reached a steady state in G2 phase. Formation of the nuclear envelope and assembly of nuclear pores occurred in the absence of microtubules or F-actin, but not if both were disrupted. Thus, the basic principles of nuclear pore complex dynamics seem to be conserved in organisms displaying open mitosis.

Specialised cellular networks of oxidoreductases coordinate the dithiol/disulfide-exchange reactions that control metabolism, protein regulation, and redox homeostasis. For probes to be selective for redox enzymes and effector proteins (nM to µM concentrations), they must also be able to resist nonspecific triggering by the ca. 50 mM background of non-catalytic cellular monothiols. However, no such selective reduction-sensing systems have yet been established. Here, we used rational structural design to independently vary thermodynamic and kinetic aspects of disulfide stability, creating a series of unusual disulfide reduction trigger units designed for stability to monothiols. We integrated the motifs into modular series of fluorogenic probes that release and activate an arbitrary chemical cargo upon reduction, and compared their performance to that of the literature-known disulfides. The probes were comprehensively screened for biological stability and selectivity against a range of redox effector proteins and enzymes. This design process delivered the first disulfide probes with excellent stability to monothiols, yet high selectivity for the key redox-active protein effector, thioredoxin. We anticipate that further applications of these novel disulfide triggers will deliver unique probes targeting cellular thioredoxins. We also anticipate that further tuning following this design paradigm will deliver redox probes for other important dithiol-manifold redox proteins, that will be useful in revealing the hitherto hidden dynamics of endogenous cellular redox systems.