Pollen grains undergo dramatic changes in cellular water potential as they deliver the male germ line to female gametes, and it has been proposed that mechanosensitive ion channels may sense the resulting mechanical stress. Here, we identify and characterize MscS-like 8 (MSL8), a pollen-specific, membrane tension–gated ion channel required for pollen to survive the hypoosmotic shock of rehydration and for full male fertility. MSL8 negatively regulates pollen germination but is required for cellular integrity during germination and tube growth. MSL8 thus senses and responds to changes in membrane tension associated with pollen hydration and germination. These data further suggest that homologs of bacterial MscS have been repurposed in eukaryotes to function as mechanosensors in multiple developmental and environmental contexts.

Transferrin is a well-studied ligand for tumor targeting due to upregulation of transferrin receptors in numerous cancer cell types. Here, we report the development of a transferrin-modified, cyclodextrin polymer-based gene delivery system. The delivery system is comprised of a nanoparticle (formed by condensation of a cyclodextrin polycation with nucleic acid) that is surface-modified to display poly(ethylene glycol) (PEG) for increasing stability in biological fluids and transferrin for targeting of cancer cells that express transferrin receptor. A transferrin-PEG-adamantane conjugate is synthesized for nanoparticle modification. The transferrin conjugate retains high receptor binding and self-assembles with the nanoparticles by adamantane (host) and particle surface cyclodextrin (guest) inclusion complex formation. At low transferrin modification, the particles remain stable in physiologic salt concentrations and transfect K562 leukemia cells with increased efficiency over untargeted particles. The increase in transfection is eliminated when transfections are conducted in the presence of excess free transferrin. The transferrin-modified nanoparticles are appropriate for use in the systemic delivery of nucleic acid therapeutics for metastatic cancer applications.

6(A),6(D)-Bis-(2-amino-2-carboxylethylthio)-6(A),6(D)-dideoxy-beta-cyclodextrin 1, a diamino acid derivative of beta-cyclodextrin, is synthesized and condensed with difunctionalized PEG comonomers to give linear, high molecular weight (M(w) over 50 kDa) beta-cyclodextrin-based polymers (2-4) with pendant functionality (carboxylate). 2-4 are all highly soluble in aqueous solutions (over 200 mg/mL). 20-O-trifluoroglycinylcamptothecin, 5a, and 20-O-trifluoroglycinylglycinylglycinylcamptothecin, 5b, are synthesized and conjugated to 2 to give polymer-camptothecin (CPT) prodrugs. The solubility of CPT is increased by more than three orders of magnitude when it is conjugated to 2. The rates of CPT release from the conjugates HGGG6 (high molecular weight polymer (M(w) 97 kDa), glyglygly linker and 6 wt % CPT loading) and HG6 (high MW polymer (M(w) 97 kDa), gly linker and 6 wt % CPT loading) in either mouse or human plasma are dramatically accelerated over the rates of pure hydrolysis at pH = 7.4, indicating the presence of enzymatic cleavage as a rate-determining step at this pH in the release of the CPT. The pH of aqueous solution has a large effect on hydrolysis rate of CPT from HGGG6 and HG6; the lower the pH, the slower the rate in the range at 4.1

To understand how chloroquine (CQ) enhances transgene expression in polycation-based, nonviral gene delivery systems, a number of CQ analogues with variations in the aliphatic amino side chain or in the aromatic ring are synthesized and investigated. Our studies indicate that the aliphatic amino moiety of CQ is essential to provide increased gene expression. Further, the enhancements are more dramatically affected by changes to the aromatic ring and are positively correlated to the strength of intercalation between DNA and the CQ analogues. Quinacrine (QC), a CQ analogue with a fused acridinyl structure that can strongly intercalate DNA, enhances transfection similarly to CQ at a concentration 10 times lower, while N(4)-(4-pyridinyl)-N(1),N(1)-diethyl-1,4-pentanediamine (CP), a CQ analogue that has a weakly intercalating pyridinyl ring, shows no effect on gene expression. Subtle change on the 7-substituent of the chloroquine aromatic structure can also greatly affect the ability of the CQ analogues to enhance transgene expression. Transfection in the presence of N(4)-(7-trifluoromethyl-4-quinolinyl)-N(1),N(1)-diethyl-1,4-pentanediamin e (CQ7a) shows expression efficiency 10 times higher than in the presence of CQ at same concentration, while transfection in the presence of N(4)-(4-quinolinyl)-N(1),N(1)-diethyl-1,4-pentanediamine (CQ7b) does not reveal any enhancing effects on expression. Through a number of comparative studies with CQ and its analogues, we conclude that there are at least three mechanistic features of CQ that lead to the enhancement in gene expression: (i) pH buffering in endocytic vesicles, (ii) displacement of polycations from the nucleic acids in polyplexes, and (iii) alteration of the biophysical properties of the released nucleic acid.

The recent introduction of the European green crab Carcinus maenas and Asian shore crab Hemigrapsus sanguineus to the west and east coasts of North America, respectively, presents a unique opportunity for investigation into competitive dynamics among intertidal crabs. Juvenile C. maenas utilize rocks, shell, and other cover, and their arrival on the west coast places them in potential competition for these resources with an abundant native grapsid, H. oregonensis. Similarly, H. sanguineus use intertidal shelter on the east coast, thus placing C. maenas in possible competition with grapsids both as an invader on the west coast and as 'resident' on the east coast, having been established there for more than 150 yr. Field sampling and laboratory experiments testing competition for space between C. maenas and Hemigrapsus spp. of equal carapace width were conducted on both coasts, as were videotaped feeding trials to examine and quantify agonistic interactions between species. When competing for food (a single damaged, anchored bivalve), C. maenas dominated over H. oregonensis, while H. sanguineus were overwhelmingly dominant over C. maenas. Within-quadrat, stratified sampling of rocks and sand revealed striking differences in habitat utilization by C. maenas living in the presence or absence of Hemigrapsus. Only ~20% of juvenile C. maenas occurred under rocks in areas occupied by either Hemigrapsus species, while north of the present distribution of H. sanguineus (in Maine) > 97% of the C. maenas were found beneath rocks. This pattern was reflected in laboratory trials as well, where both species of Hemigrapsus consistently dominated in contests for shelter. Given the importance of intertidal cover for small crabs, such competitive interactions will likely affect patterns of habitat use by C. maenas on the east coast and may have important implications for the ultimate distribution and impact of this species in the northeastern Pacific.

Understanding the energy flow in quantum dot solids represents an important step toward designing artificial systems with configurable optoelectronic properties. The growing complexity of nanoparticle assemblies and deposition techniques calls for advanced methods of characterization and control of the underlying exciton diffusion, which is pervasive in these materials. Along these lines, the Perspective will review recent strategies for measuring the energy transfer processes in assemblies of semiconductor nanocrystals with particular emphasis on emerging avant-garde characterization techniques. We will also shed light on novel experimental methods for controlling the energy diffusion in quantum dots solids, highlighting the role of assembly architecture in ensuing processes of exciton diffusion and dissociation. Novel energy transfer mechanisms recently observed in perovskite quantum dots and triplet-sensitizer nanocrystals will also be discussed.

Mitochondria must maintain tight control over the electrochemical gradient across their inner membrane to allow ATP synthesis while maintaining a redox-balanced electron transport chain and avoiding excessive reactive oxygen species production. However, there is a scarcity of knowledge about the ion transporters in the inner mitochondrial membrane that contribute to control of membrane potential. We show that loss of MSL1, a member of a family of mechanosensitive ion channels related to the bacterial channel MscS, leads to increased membrane potential of Arabidopsis mitochondria under specific bioenergetic states. We demonstrate that MSL1 localises to the inner mitochondrial membrane. When expressed in E. coli, MSL1 forms a stretch-activated ion channel with a slight preference for anions and provides protection against hypo-osmotic shock. In contrast, loss of MSL1 in Arabidopsis did not prevent swelling of isolated mitochondria in hypo-osmotic conditions. Instead, our data suggest that ion transport by MSL1 leads to dissipation of mitochondrial membrane potential when it becomes too high. The importance of MSL1 function was demonstrated by the observation of a higher oxidation state of the mitochondrial glutathione pool in msl1-1 mutants under moderate heat- and heavy-metal-stress. Furthermore, we show that MSL1 function is not directly implicated in mitochondrial membrane potential pulsing but is complementary and appears to be important under similar conditions.

Chloroplasts must divide repeatedly to maintain their population during plant growth and development. A number of proteins required for chloroplast division have been identified, and the functional relationships between them are beginning to be elucidated. In both chloroplasts and bacteria, the future site of division is specified by placement of the Filamentous temperature sensitive Z (FtsZ) ring, and the Min system serves to restrict FtsZ ring formation to mid-chloroplast or mid-cell. How the Min system is regulated in response to environmental and developmental factors is largely unstudied. Here, we investigated the role in chloroplast division played by two Arabidopsis thaliana homologs of the bacterial mechanosensitive (MS) channel MscS: MscS-Like 2 (MSL2) and MSL3. Immunofluorescence microscopy and live imaging approaches demonstrated that msl2 msl3 double mutants have enlarged chloroplasts containing multiple FtsZ rings. Genetic analyses indicate that MSL2, MSL3, and components of the Min system function in the same pathway to regulate chloroplast size and FtsZ ring formation. In addition, an Escherichia coli strain lacking MS channels also showed aberrant FtsZ ring assembly. These results establish MS channels as components of the chloroplast division machinery and suggest that their role is evolutionarily conserved.