Souffle/Spastizin controls secretory vesicle maturation during zebrafish oogenesis.

During oogenesis, the egg prepares for fertilization and early embryogenesis. As a consequence, vesicle transport is very active during vitellogenesis, and oocytes are an outstanding system to study regulators of membrane trafficking. Here, we combine zebrafish genetics and the oocyte model to identify the molecular lesion underlying the zebrafish souffle (suf) mutation. We demonstrate that suf encodes the homolog of the Hereditary Spastic Paraplegia (HSP) gene SPASTIZIN (SPG15). We show that in zebrafish oocytes suf mutants accumulate Rab11b-positive vesicles, but trafficking of recycling endosomes is not affected. Instead, we detect Suf/Spastizin on cortical granules, which undergo regulated secretion. We demonstrate genetically that Suf is essential for granule maturation into secretion competent dense-core vesicles describing a novel role for Suf in vesicle maturation. Interestingly, in suf mutants immature, secretory precursors accumulate, because they fail to pinch-off Clathrin-coated buds. Moreover, pharmacological inhibition of the abscission regulator Dynamin leads to an accumulation of immature secretory granules and mimics the suf phenotype. Our results identify a novel regulator of secretory vesicle formation in the zebrafish oocyte. In addition, we describe an uncharacterized cellular mechanism for Suf/Spastizin activity during secretion, which raises the possibility of novel therapeutic avenues for HSP research.

Noncovalently Functionalized Sulfated Castor Oil-Graphene Oxide-Strengthened Polyetherimide Composite Membranes for Superior Separation of Organic Pollutants and Their Fouling Mitigation.

A novel sulfated castor oil (SCO)-graphene oxide (GO)-strengthened polyetherimide (PEI) membrane was prepared for the first time via phase inversion process for the efficient separation of multiple organic pollutants with superior long-term antifouling stability. X-ray diffraction, attenuated total reflectance-Fourier transfer infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and mechanical strength studies revealed that the SCO and GO were successfully incorporated into the PEI membrane with enhanced mechanical strength. The water flux of the PEI/SCO@GO membrane (410.6 L m-2 h-1) was about 50 times that of bare PEI (7.8 L m-2 h-1) and about 6 times that of PEI/SCO (64.5 L m-2 h-1) membranes. The surface hydrophilicity of the PEI/SCO@GO membrane was significantly increased in terms of the decrease of the water contact angle from 98.5° (bare PEI) to 40.4°. The PEI/SCO@GO membrane separation efficiency was found to be greater than 99.0%, particularly for both the oil-in-water emulsion and the humic acid solution, respectively. Because of the higher flux recovery ratio and the lower total fouling rate of the PEI/SCO@GO membrane, a comprehensive antifouling performance was observed during the long-term foulant filtration cycle analyses. Hence, the incorporation of both SCO and GO into the PEI matrix would render the highly hydrophobic PEI material as the suitable and desirable antifouling membrane toward the treatment of various organic foulants in wastewater.

Separation and preconcentration of arsenite and other heavy metal ions using graphene oxide laminated with protein molecules.

The graphene oxide surface was laminated with bovine serum albumin (BSA) followed by the directional flow through a membrane to prepare a free-standing PLGO (protein laminated GO) composite. BSA immobilization increased the interlayer spacing of GO and led to the formation of capillaries. The column packed with PLGO adsorbent permeated water faster as much as ca. 5 fold as compared to only GO packed column. The PLGO composite was used to develop a solid phase extraction method for the selective preconcentration of As(III) in the presence of As(V), prior to their determination. As(III) binding to sulfhydryl groups of BSA in PLGO plays a key role in the speciation. The coexisting heavy metal ions did not hinder the recovery of trace As(III). The method was advantageously employed for the preconcentration of As(III), Pb(II), Cd(II), Zn(II), Cu(II) and Ni(II) from water and food samples. A 3 mL of 1 M hydrochloric acid would be adequate for the complete desorption (recovery > 99%) of the adsorbed metal ions. The preconcentration limit achieved for As(III), Pb(II), Cd(II), Zn(II), Cu(II) and Ni(II) were 1.7, 2.0, 2.0, 2.0, 1.8 and 2.0 µg L-1 respectively, with an optimized sample flow rate of 10 mL min-1.

Towards improved protein anti-fouling and anti-microbial properties of poly (vinylidene fluoride) membranes by blending with lactate salts-based polyurea as surface modifiers.

It is a big challenge to develop membrane fouling-resistant materials for long-term water filtration applications in order to reduce the operating cost. Herein, for the first time, we have proposed the utilization of lactate salts-based polyurea additives as surface modifiers (SMs) to endow anti-microbial and anti-protein activities which increase the life of poly (vinylidene fluoride) (PVDF) membrane filters in terms of attaining anti-fouling properties for prolonged and stable water flux in water treatment. Membrane fouling was examined by taking into account the important influencing factors such as surface hydrophilicity and functional lactate groups present on the surface. The results showed that the surface hydrophilicity was enhanced leading to higher water flux of the PVDF membrane blended with sodium lactate-based polyurea (Na-PVDF) (174.2 L m-2 h-1), which was almost 12 times higher than that of the neat PVDF membrane. The fabricated SMs-blended PVDF membranes displayed satisfactory rejection and fouling resistant performance for the bovine serum albumin (BSA) molecules. The PVDF membrane blended with zinc lactate-based polyurea (Zn-PVDF) ensured effective anti-microbial activity against bacteria and fungi. Besides, the SMs-blended PVDF membranes displayed a higher zone of inhibition (ZOI) and higher colony reduction than the neat PVDF membranes in the anti-microbial test. The long-term water filtration test carried out after 200 days showed that PVDF membranes blended with SMs retained more than 90% of the original water flux, suggesting the long-term stability of SMs in the PVDF matrix. Therefore, the synergistic effect of SMs can be considered as an important life enhancer of polymeric membrane materials in the field of membrane technology.

Nanofiltration Membranes with Metal Cation-Immobilized Aminophosphonate Networks for Efficient Heavy Metal Ion Removal and Organic Dye Degradation.

Modifications to the surface of polymeric membranes to integrate supplemental properties like surface charge or catalytic activity are the cornerstone of the membrane process advancement to effectuate improvements in functionality and selectivity. Herein, a new approach is demonstrated to construct nanofiltration membranes with a metal-organic coordinated selective layer. Polyethylenimine (PEI) was integrated with phosphite linkages to form a characteristic aminophosphonate ester polymer based on the Kabachnik-Fields reaction, and a thin polymer layer was deposited on an ultrafiltration (UF) membrane to form the aminophosphonate networks surface-modified membranes. The aminophosphonate polymer interlayer facilitated the immobilization of metal cation moieties through the strong coordinative chemical bonding with the amino groups and phosphite moieties. Typically, the incorporated Fe3+ strengthened the membranes' electropositivity leading to excellent heavy metal ion removal (>98%) and efficient organic dye separation (>99.8%). Meanwhile, the strategy also enabled the embedment of a photocatalytic layer comprising nanoneedle-like α-FeOOH that endowed the membrane with high photo-Fenton activity for organic dye mineralization. Subsequently, the α-FeOOH-embedded membrane afforded the photocatalytic self-cleaning potentiality for organic fouling mitigation. This contribution underscores the prospect of advancing the integration of metal-specific functionalities and the membrane process for advanced membrane technologies in water treatment.

High-Pressure Freezing Electron Microscopy of Zebrafish Oocytes.

Oogenesis is an essential cellular and developmental process to prepare the oocyte for propagation of a species after fertilization. Oocytes of oviparous animals are enormous cells endowed with many, big cellular compartments, which are interconnected through active intracellular transport. The dynamic transport pathways and the big organelles of the oocyte provide the opportunity to study cellular trafficking with outstanding resolution. Hence, oocytes were classically used to investigate cellular compartments. Though many novel regulators of vesicle trafficking have been discovered in yeast, tissue culture cells and invertebrates, recent forward genetic screens in invertebrate and vertebrate oocytes isolated novel control proteins specific to multicellular organisms. Zebrafish is a widely used vertebrate model to study cellular and developmental processes in an entire animal. The transparency of zebrafish embryos allows following cellular events during early development with in vivo imaging. Unfortunately, the active endocytosis of the oocyte also represents a drawback for imaging. The massive amounts of yolk globules prevent the penetration of light-beams and currently make in vivo microscopy a challenge. As a consequence, electron microscopy (EM) still provides the highest resolution to analyze the ultra-structural details of compartments and organelles and the mechanisms controlling many cellular pathways of the oocyte. Among different fixation approaches for EM, High Pressure Freezing (HPF) in combination with freeze substitution significantly improves the samples preservation closest to their natural status. Here, we describe the HPF with freeze substitution embedding method for analyzing cellular processes in zebrafish oocytes using electron microscopy.