Golgi Apparatus

Membrane-enveloped vesicles travel among the compartments of the cytoplasm of eukaryotic cells, delivering their specific cargo to programmed locations by membrane fusion. The pairing of vesicle v-SNAREs (soluble N-ethylmaleimide-sensitive factor attachment protein receptors) with target membrane t-SNAREs has a central role in intracellular membrane fusion. We have tested all of the potential v-SNAREs encoded in the yeast genome for their capacity to trigger fusion by partnering with t-SNAREs that mark the Golgi, the vacuole and the plasma membrane. Here we find that, to a marked degree, the pattern of membrane flow in the cell is encoded and recapitulated by its isolated SNARE proteins, as predicted by the SNARE hypothesis.

We examined the cellular localization of nine different connexin32 (Cx32) mutants associated with X-linked Charcot-Marie-Tooth disease (CMTX) in communication-incompetent mammalian cells. Cx32 mRNA was made, but little or no protein was detected in one class of mutants. In another class of mutants, Cx32 protein was detectable in the cytoplasm and at the cell surface, where it appeared as plaques and punctate staining. Cx32 immunoreactivity in a third class of mutants was restricted to the cytoplasm, where it often colocalized with the Golgi apparatus. Our studies suggest that CMTX mutations have a predominant effect on the trafficking of Cx32 protein, resulting in a potentially toxic cytoplasmic accumulation of Cx32 in these cells. These results and evidence of cytoplasmic accumulation of other mutated myelin proteins suggest that diseases affecting myelinating cells may share a common pathophysiology.

BackgroundSpaced-repetition and test-enhanced learning are two methodologies that boost knowledge retention. ALERT STUDENT is a platform that allows creation and distribution of Learning Objects named flashcards, and provides insight into student judgments-of-learning through a metric called `recall accuracy`. This study aims to understand how the spaced-repetition and test-enhanced learning features provided by the platform affect recall accuracy, and to characterize the effect that students, flashcards and repetitions exert on this measurement.MethodsThree spaced laboratory sessions (s0, s1 and s2), were conducted with n=96 medical students. The intervention employed a study task, and a quiz task that consisted in mentally answering open-ended questions about each flashcard and grading recall accuracy. Students were randomized into study-quiz and quiz groups. On s0 both groups performed the quiz task. On s1 and s2, the study-quiz group performed the study task followed by the quiz...

Carnivorous plants trap and utilize animals in order to improve their supply with mineral nutrients. One strategy for prey capture is the use of adhesive traps, i.e., leaves that produce sticky substances. Sticky shoots are widespread in the plant kingdom and serve to protect the plant, especially flowers and seeds. In some taxa, mechanisms have been developed to absorb nutrients from the decaying carcasses of animals killed by the glue. In carnivorous plants sensu stricto, additional digestive enzymes are secreted into the glue to accelerate degradation of prey organisms. The glues are secreted by glands that are remarkably uniform throughout all taxa producing adhesive traps. They follow the general scheme of plant glandular organs: the glands consist of a stalk, a neck equipped with a suberin layer that separates the gland from the rest of the plant, and the glandular cells producing sticky secretions. This glue always forms droplets at the tip of the glandular hairs. In most genera, these glands produce only glue whereas enzymes for prey digestion are secreted by a second type of gland. Two types of glue can be distinguished, polysaccharide mucilage in Droseraceae, Lentibulariaceae and their relatives, and terpenoid resins in Roridulaceae. On the ultrastructural level, mucilage is produced by the Golgi apparatus. Resins can be expected to be produced by the endoplasmic reticulum and by leucoplasts. Adhesive traps are suitable not only for the capture of small animals but also for the collection of organic particles like pollen grains. The glue may contain toxic compounds but the prey usually dies from suffocation by clogging of its tracheae. In Pinguicula and Drosera, the performance of the traps is improved by a slow movement, i.e., the folding of the leaf around the prey animal upon stimulation. In some species of Nepenthes, a pitcher with smooth walls is filled with a sticky digestive fluid. Some organisms, however, have developed strategies to survive on the deadly traps. Several species of Hemiptera are able to walk on the sticky traps and nourish on the prey; their faeces are absorbed by the plant. In Roridula, this relationship is highly specialized and essential for both the plant and the insect. Mutualistic fungi and bacteria are common in many adhesive traps where they degrade and dissolve the plant’s prey. The traps of Drosera, on the other hand, are virtually sterile. In spite of the extensive literature on adhesive traps, numerous questions still remain. Only a small percentage of “sticky” plants have actually been tested for carnivory. The properties and composition of their glues are widely unknown. In advanced adhesive traps, the mechanisms regulating secretion and absorption are poorly understood. Thereby, some glues may be applicable for human as they are non-toxic, quite stable under environmental conditions, and partly exhibit mildly antibiotic properties. Some carnivorous plants with adhesive traps have been used by humans for the capture of insects as well as for food processing.

The effects of an additional keto group on absorption wavelength and the corresponding metal complexes Zn(II), Cu(II) In(III) on singlet oxygen production and photodynamic efficacy were examined among the alkyl ether analogs of pyropheophorbide-a. For the preparation of the desired photosensitizers, the methyl 13(2)-oxo-pyropheophorbide-a obtained by reacting methyl pyropheophorbide-a with aqueous LiOH-THF was converted into a series of alkyl ether analogs. These compounds were evaluated for photophysical properties and in vitro (by means of the MTT assay and intracellular localization in RIF cells) and in vivo (in C3H mice implanted with RIF tumors) photosensitizing efficacy. Among the alkyl ether derivatives, the methyl 3-decyloxyethyl-3-devinyl-13(2)-oxo-pyropheophorbide-a was found to be most effective and the insertion of In(III) into this analog further enhanced its in vitro and in vivo photosensitizing efficacy. Fluorescence microscopy showed that, in contrast to the hexyl and dodecyl ether derivatives of HPPH (which localize in mitochondria and lysosomes, respectively), the diketo-analogs and their In(III) complexes localized in Golgi bodies. The preliminary in vitro and in vivo results suggest that, in both free-base and metalated analogs, the introduction of an additional keto group at the five-member exocyclic ring in pyropheophorbide-a diminishes its photosensitizing efficacy. This may be due to a shift in subcellular localization from mitochondria to the Golgi bodies. The further introduction of In(III) enhances photoactivity, but not by shifting the localization of the photosensitizer.

The cytology of epithelial cells with apical nuclei in the initial segment of the rat epididymis was studied with the light and electron microscopes. Two types of cells were distinguished and were designated apical cells and narrow cells. The apical cells are more numerous than the narrow cells and closely resemble principal cells except for the location of the nucleus. They probably correspond to the apical cells of Reid and Cleland (′57) and may represent a variation of the principal cell. The narrow cells differ markedly from the apical cells in both light microscopic appearance and fine structure. Narrow cells stain intensely with toluidine blue and are characterized by a slender shape, many mitochondria with tubular cristae, and a large number of apical cup-shaped cytoplasmic vesicles. The possible relationship of narrow cells to other cell types is discussed.