The role of FlhF and HubP as polar landmark proteins in Shewanella putrefaciens CN‐32

Spatiotemporal regulation of cell polarity plays a role in many fundamental processes in bacteria and often relies on ‘landmark’ proteins which recruit the corresponding clients to their designated position. Here, we explored the localization of two multi‐protein complexes, the polar flagellar motor and the chemotaxis array, in Shewanella putrefaciens CN‐32. We demonstrate that polar positioning of the flagellar system, but not of the chemotaxis system, depends on the GTPase FlhF. In contrast, the chemotaxis array is recruited by a transmembrane protein which we identified as the functional ortholog of Vibrio cholerae HubP. Mediated by its periplasmic N‐terminal LysM domain, SpHubP exhibits an FlhF‐independent localization pattern during cell cycle similar to its Vibrio counterpart and also has a role in proper chromosome segregation. In addition, while not affecting flagellar positioning, SpHubP is crucial for normal flagellar function and is involved in type IV pili‐mediated twitching motility. We hypothesize that a group of HubP/FimV homologs, characterized by a rather conserved N‐terminal periplasmic section required for polar targeting and a highly variable acidic cytoplasmic part, primarily mediating recruitment of client proteins, serves as polar markers in various bacterial species with respect to different cellular functions.     

The Phosphatidylinositol (3,4,5)-Trisphosphate-dependent Rac Exchanger 1·Ras-related C3 Botulinum Toxin Substrate 1 (P-Rex1·Rac1) Complex Reveals the Basis of Rac1 Activation in Breast Cancer Cells

The P-Rex (phosphatidylinositol (3,4,5)-trisphosphate (PIP₃)-dependent Rac exchanger) family (P-Rex1 and P-Rex2) of the Rho guanine nucleotide exchange factors (Rho GEFs) activate Rac GTPases to regulate cell migration, invasion, and metastasis in several human cancers. The family is unique among Rho GEFs, as their activity is regulated by the synergistic binding of PIP₃ and Gβγ at the plasma membrane. However, the molecular mechanism of this family of multi-domain proteins remains unclear. We report the 1.95 Å crystal structure of the catalytic P-Rex1 DH-PH tandem domain in complex with its cognate GTPase, Rac1 (Ras-related C3 botulinum toxin substrate-1). Mutations in the P-Rex1·Rac1 interface revealed a critical role for this complex in signaling downstream of receptor tyrosine kinases and G protein-coupled receptors. The structural data indicated that the PIP₃/Gβγ binding sites are on the opposite surface and markedly removed from the Rac1 interface, supporting a model whereby P-Rex1 binding to PIP₃ and/or Gβγ releases inhibitory C-terminal domains to expose the Rac1 binding site.     

Ecotoxicity impact assessment of laundry products: a comparison of USEtox and critical dilution volume approaches

Purpose  

There is an increasing interest in the assessment and comparison of the environmental impacts of consumer products. Schemes such as Grenelle de l’Environnement, currently under development in France, aim to assess and communicate the life cycle impacts of consumer products. Freshwater ecotoxicity is one of the impact categories under consideration. This paper presents the results of a comparison of USEtox and critical dilution volume (CDV) approaches for assessing laundry products.     

A novel mode of chromosomal evolution peculiar to filamentous Ascomycete fungi

Background  

Gene loss, inversions, translocations, and other chromosomal rearrangements vary among species, resulting in different rates of structural genome evolution. Major chromosomal rearrangements are rare in most eukaryotes, giving large regions with the same genes in the same order and orientation across species. These regions of macrosynteny have been very useful for locating homologous genes in different species and to guide the assembly of genome sequences. Previous analyses in the fungi have indicated that macrosynteny is rare; instead, comparisons across species show no synteny or only microsyntenic regions encompassing usually five or fewer genes. To test the hypothesis that chromosomal evolution is different in the fungi compared to other eukaryotes, synteny was compared between species of the major fungal taxa.     

Engaging neuroscience to advance translational research in brain barrier biology

The delivery of many potentially therapeutic and diagnostic compounds to specific areas of the brain is restricted by brain barriers, of which the most well known are the blood-brain barrier (BBB) and the blood-cerebrospinal fluid (CSF) barrier. Recent studies have shown numerous additional roles of these barriers, including an involvement in neurodevelopment, in the control of cerebral blood flow, and--when barrier integrity is impaired--in the pathology of many common CNS disorders such as Alzheimer's disease, Parkinson's disease and stroke.     

A mutation in synaptojanin 2 causes progressive hearing loss in the ENU-mutagenised mouse strain Mozart

Background

Hearing impairment is the most common sensory impairment in humans, affecting 1∶1,000 births. We have identified an ENU generated mouse mutant, Mozart, with recessively inherited, non-syndromic progressive hearing loss caused by a mutation in the synaptojanin 2 (Synj2), a central regulatory enzyme in the phosphoinositide-signaling cascade.

Methodology/Principal Findings

The hearing loss in Mozart is caused by a p.Asn538Lys mutation in the catalytic domain of the inositol polyphosphate 5-phosphatase synaptojanin 2. Within the cochlea, Synj2 mRNA expression was detected in the inner and outer hair cells but not in the spiral ganglion. Synj2 ^N538K mutant protein showed loss of lipid phosphatase activity, and was unable to degrade phosphoinositide signaling molecules. Mutant Mozart mice (Synj2 ^N538K/N538K) exhibited progressive hearing loss and showed signs of hair cell degeneration as early as two weeks of age, with fusion of stereocilia followed by complete loss of hair bundles and ultimately loss of hair cells. No changes in vestibular or neurological function, or other clinical or behavioral manifestations were apparent.

Conclusions/Significance

Phosphoinositides are membrane associated signaling molecules that regulate many cellular processes including cell death, proliferation, actin polymerization and ion channel activity. These results reveal Synj2 as a critical regulator of hair cell survival that is essential for hair cell maintenance and hearing function.