Postinsemination changes in the amoeboid sperm of a nematode,nippostrongylus brasiliensis

Nematode sperm undergo a capacitationlike change called activation, after insemination into the female reproductive tract. In this paper we examine the morphological and functional consequences of activation of the sperm of Nippostrongylus brasiliensis by comparing the ultrastructure of sperm in the reproductive tracts of males and females and by analysing locomotion using time-lapse cinematography. Sperm in males consist of a long tail, composed of highly condensed chromatin, and a cytoplasmic region containing numbrane-bound secretory products of the Golgi called membranous organelles (MOs) as well as mitochondria. Following activation, the MOs fuse with the plasma membrane, release their electron-dense contents, and remain connected to the outside by a narrow channel. A small region at the anterior of sperm from males is amoeboid and can produce small pseudopodia. In sperm from the uterus this region enlarges considerably, the groundplasm changes from a granular to a filamentous from and the sperm become fully motile. During locomotion a cycle of events occurs at the leading edge beginning with the extension of a small pseudopodium. A constriction ring forms across its base and as the sperm progresses the constriction ring moves back along the cell, but remains stationary relative to the substrate. The location of new pseudopodia at the leading edge dictates the direction of movement of the spermatozoon. Since Cytochalasin B had no effect on the translocation of sperm, the polymerization of actin appears not to play a part in locomotion.     

Fine structure of gels prepared from an actin-binding protein and actin: comparison to cytoplasmic extracts and cortical cytoplasm in amoeboid cells of cortical cytoplasm in amoeboid cells of Dictyostelium discoideum

We have identified the three-dimensional ultrastructure of actin gels that are formed in well-characterized cell extracts and mixtures of purified actin and the 120K actin-binding protein and compared these to the ultrastructure of the cytoplasmic matrix in regions of nonextracted Dictyostelium amoebae that are rich in actin and 120K. This ultrastructural characterization was achieved by using critical-point-dried whole-mount preparations. All three preparations--gelled extracts, purified proteins, and cortical cytoplasm--are composed of filament networks. The basic morphological feature of these networks is the presence of contacts between convergent filaments resulting in "T" or "X" shaped contacts. The finding that actin-containing gels are composed of filament networks, where the primary interaction occurs between convergent filaments, reconciles the known requirement of F actin for gelation with the amorphous appearance of these gels in thin sections. Increasing the molar ratio of 120K dimer to actin monomer increases the number of contacts between filaments per unit volume and decreases the lengths of filaments between contacts. This indicates that 120K stabilizes interactions between filaments and is consistent with biochemical evidence that 120K crosslinks actin filaments. The cortical network in situ resembles more closely networks formed in 120K-rich extracts than networks assembled in mixtures of purified 120K and actin. The heterogeneity of filament diameters and variation of network density are properties shared by extracts and the cytomatrix in situ while networks found in purified 120K-actin gels have filament diameters and densities that are more uniform. These differences are certainly due to the more complex composition of cell extracts and cortical cytoplasm as compared to that of purified 120K-actin gels.     

Large oncosomes mediate intercellular transfer of functional microRNA

Prostate cancer cells release atypically large extracellular vesicles (EVs), termed large oncosomes, which may play a role in the tumor microenvironment by transporting bioactive molecules across tissue spaces and through the blood stream. In this study, we applied a novel method for selective isolation of large oncosomes applicable to human platelet-poor plasma, where the presence of caveolin-1-positive large oncosomes identified patients with metastatic disease. This procedure was also used to validate results of a miRNA array performed on heterogeneous populations of EVs isolated from tumorigenic RWPE-2 prostate cells and from isogenic non-tumorigenic RWPE-1 cells. The results showed that distinct classes of miRNAs are expressed at higher levels in EVs derived from the tumorigenic cells in comparison to their non-tumorigenic counterpart. Large oncosomes enhanced migration of cancer-associated fibroblasts (CAFs), an effect that was increased by miR-1227, a miRNA abundant in large oncosomes produced by RWPE-2 cells. Our findings suggest that large oncosomes in the circulation report metastatic disease in patients with prostate cancer, and that this class of EV harbors functional molecules that may play a role in conditioning the tumor microenvironment.     

几种黏菌黏变形体形态及运动特征

黏菌黏变形体结构对变形运动方式具有影响,在显微镜下观察了长期培养中的5种黏菌的黏变形体的形态及运动特征。结果表明:不同种类的黏菌黏变形体形态差别较大,主要是透明外质的有无、形态规则或不规则。运动特征上有滑动型、流动型和爬行运动方式,运动方式和透明外质结构有关,透明外质较厚很难形成典型的伪足,表现为滑动运动方式,移动速度较慢。     

KIF13A‐regulated RhoB plasma membrane localization governs membrane blebbing and blebby amoeboid cell migration

Membrane blebbing‐dependent (blebby) amoeboid migration can be employed by lymphoid and cancer cells to invade 3D‐environments. Here, we reveal a mechanism by which the small GTPase RhoB controls membrane blebbing and blebby amoeboid migration. Interestingly, while all three Rho isoforms (RhoA, RhoB and RhoC) regulated amoeboid migration, each controlled motility in a distinct manner. In particular, RhoB depletion blocked membrane blebbing in ALL (acute lymphoblastic leukaemia), melanoma and lung cancer cells as well as ALL cell amoeboid migration in 3D‐collagen, while RhoB overexpression enhanced blebbing and 3D‐collagen migration in a manner dependent on its plasma membrane localization and down‐stream effectors ROCK and Myosin II. RhoB localization was controlled by endosomal trafficking, being internalized via Rab5 vesicles and then trafficked either to late endosomes/lysosomes or to Rab11‐positive recycling endosomes, as regulated by KIF13A. Importantly, KIF13A depletion not only inhibited RhoB plasma membrane localization, but also cell membrane blebbing and 3D‐migration of ALL cells. In conclusion, KIF13A‐mediated endosomal trafficking modulates RhoB plasma membrane localization to control membrane blebbing and blebby amoeboid migration.     

Ptolemeba n. gen., a Novel Genus of Hartmannellid Amoebae (Tubulinea,Amoebozoa); with an Emphasis on the Taxonomy of Saccamoeba

Hartmannellid amoebae are an unnatural assemblage of amoeboid organisms that are morphologically difficult to discern from one another. In molecular phylogenetic trees of the nuclear‐encoded small subunit rDNA, they occupy at least five lineages within Tubulinea, a well‐supported clade in Amoebozoa. The polyphyletic nature of the hartmannellids has led to many taxonomic problems, in particular paraphyletic genera. Recent taxonomic revisions have alleviated some of the problems. However, the genus Saccamoeba is paraphyletic and is still in need of revision as it currently occupies two distinct lineages. Here, we report a new clade on the tree of Tubulinea, which we infer represents a novel genus that we name Ptolemeba n. gen. This genus subsumes a clade of hartmannellid amoebae that were previously considered in the genus Saccamoeba, but whose mitochondrial morphology is distinct from Saccamoeba. In accordance with previous research, we formalize the clade as distinct from Saccamoeba. Transmission electron microscopy of our isolates illustrate that both molecularly discrete species can be further differentiated by their unique mitochondrial cristal morphology.