Novel non-Mendelian determinant involved in the control of translation accuracy in Saccharomyces cerevisiae.

Two cytoplasmically inherited determinants related by their manifestation to the control of translation accuracy were previously described in yeast. Cells carrying one of them, [PSI(+)], display a nonsense suppressor phenotype and contain a prion form of the Sup35 protein. Another element, [PIN(+)], determines the probability of de novo generation of [PSI(+)] and results from a prion form of several proteins, which can be functionally unrelated to Sup35p. Here we describe a novel nonchromosomal determinant related to the SUP35 gene. This determinant, designated [ISP(+)], was identified as an antisuppressor of certain sup35 mutations. We observed its loss upon growth on guanidine hydrochloride and subsequent spontaneous reappearance with high frequency. The reversible curability of [ISP(+)] resembles the behavior of yeast prions. However, in contrast to known prions, [ISP(+)] does not depend on the chaperone protein Hsp104. Though manifestation of both [ISP(+)] and [PSI(+)] is related to the SUP35 gene, the maintenance of [ISP(+)] does not depend on the prionogenic N-terminal domain of Sup35p and Sup35p is not aggregated in [ISP(+)] cells, thus ruling out the possibility that [ISP(+)] is a specific form of [PSI(+)]. We hypothesize that [ISP(+)] is a novel prion involved in the control of translation accuracy in yeast.     

A permeability transition in liposomes induced by the formation of Ca/palmitic acid complexes

Formation of palmitic acid/Ca²⁺ (PA/Ca²⁺) complexes was suggested to play a key role in the non-classical permeability transition in mitochondria (NCPT), which seems to be involved in the PA-induced apoptosis of cardiomyocytes. Our previous studies of complexation of free fatty acids (FFA) with Ca²⁺ showed that long-chain (C:16-C:22) saturated FFA had an affinity to Ca²⁺, which was much higher than that of other FFA and lipids. The formation of FFA/Ca²⁺ complexes in the black-lipid membrane (BLM) was demonstrated to induce a nonspecific ion permeability of the membrane. In the present work, we have found that binding of Ca²⁺ to PA incorporated into the membrane of sulforhodamine B (SRB)-loaded liposomes results in an instant release of a part of SRB, with the quantity of SRB released depending on the concentration of PA and Ca²⁺. The pH-optimum of this phenomenon, similar to that of PA/Ca²⁺ complexation, is in the alkaline range. The same picture of SRB release has been revealed for stearic, but not for linoleic acid. Along with Ca²⁺, some other bivalent cations (Ba²⁺, Sr²⁺, Mn²⁺, Ni²⁺, Co²⁺) also induce SRB release upon binding to PA-containing liposomes, while Mg²⁺ turns out to be relatively ineffective. As revealed by fluorescence correlation spectroscopy, the apparent size of liposomes does not alter after the addition of PA, Ca²⁺ or their combination. So it has been supposed that the cause of SRB release from liposomes is the formation of lipid pores. The effect of FFA/Ca²⁺-induced permeabilization of liposomal membranes has several analogies with NCPT, suggesting that both these phenomena are of similar nature.     

Intranasal administration of mitochondria improves spatial memory in olfactory bulbectomized mice

Here, we found that functionally active mitochondria isolated from the brain of NMRI donor mice and administrated intranasally to recipient mice penetrated the brain structures in a dose-dependent manner. The injected mitochondria labeled with the MitoTracker Red localized in different brain regions, including the neocortex and hippocampus, which are responsible for memory and affected by degeneration in patients with Alzheimer''s disease. In behavioral experiments, intranasal microinjections of brain mitochondria of native NMRI mice improved spatial memory in the olfactory bulbectomized (OBX) mice with Alzheimer’s type degeneration. Control OBX mice demonstrated loss of spatial memory tested in the Morris water maze. Immunocytochemical analysis revealed that allogeneic mitochondria colocalized with the markers of astrocytes and neurons in hippocampal cell culture. The results suggest that a non-invasive route intranasal administration of mitochondria may be a promising approach to the treatment of neurodegenerative diseases characterized, like Alzheimer''s disease, by mitochondrial dysfunction.     

A PLETHORA/PIN-FORMED/auxin network mediates prehaustorium formation in the parasitic plant Striga hermonthica

The parasitic plant Striga (Striga hermonthica) invades the host root through the formation of a haustorium and has detrimental impacts on cereal crops. The haustorium results from the prehaustorium, which is derived directly from the differentiation of the Striga radicle. The molecular mechanisms leading to radicle differentiation shortly after germination remain unclear. In this study, we determined the developmental programs that regulate terminal prehaustorium formation in S. hermonthica at cellular resolution. We showed that shortly after germination, cells in the root meristem undergo multiplanar divisions. During growth, the meristematic activity declines and associates with reduced expression of the stem cell regulator PLETHORA1 and the cell cycle genes CYCLINB1 and HISTONE H4. We also observed a basal localization of the PIN-FORMED (PIN) proteins and a decrease in auxin levels in the meristem. Using the structural layout of the root meristem and the polarity of outer-membrane PIN proteins, we constructed a mathematical model of auxin transport that explains the auxin distribution patterns observed during S. hermonthica root growth. Our results reveal a fundamental molecular and cellular framework governing the switch of S. hermonthica roots to form the invasive prehaustoria.

The parasitic plant Striga hermonthica forms its invasive organ, the prehaustorium, by inducing differentiation of the radicle by arresting cell division.     

In Vitro Propagation of the Protozoan Perkinsus Marinus, A Pathogen of the Eastern Oyster, Crassostrea Virginica

ABSTRACT. Perkinsus marinus , a pathogen of eastern oysters ( Crassostrea virginica ), has been successfully propagated in vitro. Cultures of the parasite were initiated from heart fragments of an infected oyster. the cultured protozoan (designated Parkinsus -1) was similar in morphology at both the light and transmission electron microscopy levels to histozoic stages of P. marinus in naturally infected oysters. In addition, cultured cells incubated in fluid thioglycollate medium produced enlarged cells (prezoosporangia) that stained blue-black in Lugol's solution, a response characteristic to Perkinsus spp. and used in routine diagnosis. Polyclonal antibodies raised against P. marinus prezoosporangia reacted positively to Perkinsus -1. Finally, the cultured cells infected susceptible oysters and reisolation of Perkinsus -1 cells was possible from the hearts of experimentally infected oysters. the culture medium contained most of the known constituents of cell-free hemolymph of oysters. the success achieved in culturing P. marinus will allow further investigations aimed at reducing mortalities caused by this important oyster pathogen and at addressing many unanswered questions about its biology and pathobiology.     

Inhibition of the mitochondrial calcium uniporter by antibodies against a 40-kDa glycorproteinT

Polyclonal rabbit antibodies against a Ca²⁺-binding mitochondrial glycoprotein were found to inhibit the uniporter-mediated transport of Ca²⁺ in mitoplasts prepared from rat liver mitochondria. Spermine, a modulator of the uniporter, decreased the inhibition. This glycoprotein ofM _r 40,000, isolated from beef heart mitochondria and earlier shown to form Ca²⁺-conducting channels in black-lipid membranes, thus is a good candidate for being a component of the uniporter. Antibody-IgG was found to specifically bind to mitochondria in human fibroblasts.     

Plant Chromatin Replicated in the Absence of Protein Synthesis

The aim of the present work is to detect possible differencesin the chromatin of plants replicated in the absence of proteinsynthesis. The kinetics of nuclease digestion in Allium cepa L., evaluatedafter making the cells permeable, was faster for the chromatinof meristem cells replicated in the presence of 1.0 µgml^–1 cycloheximide than in control cells. In order to have a synchronous population in the meristems,cells were labelled as binucleate by a short treatment with5.0 mM caffeine. Treated cells failed to increase both theircontent in dense chromatin and intranuclear histones. Thesefacts suggest that chromatin replicated in the presence of cycloheximidedid not incorporate histones and was unable to be integratedinto dense chromatin patches. Key words: Allium cepa L., Chromatin replication, Protein synthesis     

Radiation-induced improvement of the freeze-resistance of a cold-sensitive wheat variety: Freeze-tolerance and fatty acid patterns

Effects of 3–15 krad ⁶⁰Co gamma radiation on cereal seeds were investigated with regard to the frost hardiness of leaves of 5–7-day-old seedlings. Comparative studies were carried out on the gas-chromatographically determined distribution patterns of fatty acids in different pools (total fatty acid, total lipid, polar lipids) of a cold-resistant (cv. Mironowskaya 808) and a cold-sensitive (cv. Penjamo 62) cultivar of wheat (Triticum aestivum L.). Parallelism between fatty acid distribution pattern, empirical parameters suggested for quantitative measures of cold tolerance (the ratio unsat/sat and double-bond index), and the low-temperature behaviour of shoots grown from radiation treated seeds of ‘Penjamo 62’, was also examined. To monitor differences in the fatty acid syntheses of ‘Mironowskaya 808’and ‘Penjamo 62’, and to demonstrate radiation-induced changes in fatty acid turnover a [1–¹⁴C]-acetate incorporation technique was employed. The results of practical importance are: 1. A significant improvement in the frost-resistance of the cold-sensitive ‘Penjamo 62’variety could be achieved with 6–9 krad irradiation, the half-freeze-killing temperature dropping from ?6 to about ?18°C. 2. Freeze-hardiness, no matter whether inherited or gained, could be abolished by gamma irradiation with higher dose. The following conclusions of theoretical interest can be drawn: 1. Low-temperature behaviour of plant tissues is a dynamic property rather than a static one, not only the formation but also the breakdown of certain hydrocarbon chains may be of paramount relevance in cold-tolerance. 2. Not the linolenic (18:3) component, but rather the overall distribution pattern of the C₁₈ family seems to correlate with low-temperature-responses of shoots. 3. Empirical parameters investigated do not provide reliable quantitative measures of the susceptibility to freeze (and cold-) injuries. 4. Changes in the syntheses of some key proteins (e.g. peroxidase, water-soluble proteins, etc.) may also be important in adaptation to low-temperature conditions.