ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1989.tb00868.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Myonemes of the acantharians are contractile ribbon‐like organelles. As previously shown, their motility is based on the coiling mechanism of double‐twisted 2–4 nm nonactin filaments [14]. Myonemes have been isolated and manipulatedin vitro. After demembranation, the contraction takes place when the Ca2+concentration is above 10−7M, whereas relaxation occurs below this threshold concentration. The response to Ca2+ions is an on/off mechanism. Both contraction and relaxation can be induced repeatedly without fatigue phenomena. Other divalent cations such as Sr2+, Ba2+, Ma2+, CO2+, and La3+can replace Ca2+in inducing contraction of the demembranated myonemes although with less efficiency. Contraction and relaxation are ATP‐independent and calmodulin is not involved in thisin vitromotility process. The myoneme is a strongly resistant structure which is capable of contracting and relaxing under various extreme conditions which indicates very stable proteins and resistant

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1989.tb00869.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

The myonemes in the marine pelagic protozoa Acantharia are contractile organelles involved in buoyancy regulation. It was previously shown that they can perform three kinds of movement: rapid contraction, slow undulation and slow relaxation. They consist of a periodically striated bundle of 2–4 nm nonactin filaments that are twisted in pairs and shortened by a coiling mechanism. After permeabilization or demembranation, contraction and relaxation can still be performed by varying Ca2+concentration and ATP is not needed.In the present paper, we have studied the role of Ca2+and inhibitors of energy production in intact cells. Our data suggest that; (i) thein vivorapid contraction subsequent to mechanical or electrical stimulation is triggered by Ca2+influx across the cell membrane; (ii) the slow contraction that takes place during the undulating movement depends on Ca2+release provided by internal calcium stores; (iii) the rapid contraction as well as the progressive shortening that occurs during the slow undulating movement are caused by Ca2+binding to the myoneme filaments; (iv) ATP is not directly involved in the saturation by Ca2+of Ca2+sensitive sites located along the myoneme microstrands; (v) regulation of the movements of Ca2+within the cytoplasm depends mainly upon the alternative pathway of ATP production; (vi) calmodulin is presumably involved in this regulation. A tentative cytophysiologic interpretation of the mechanism of contractility is propose

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1989.tb00870.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Our freeze‐fracture study has revealed the presence of two types of intramembrane particle (IMP) aggregates in the somatic plasma membrane ofEufolliculina uhligi: rectangular particle arrays and rosettes. Their morphology and distribution differ in the motile and in the lorica secreting stage. Rectangular particle arrays occur to the left of the kineties. They are not very obvious in the swarmer, but increase in size and number during lorica formation. We discuss whether they are involved in the contractility of this ciliate. Rosettes occur to the right of the kinetics where they mark attachment sites of extrusive vesicles at the plasma membrane of the swarmer. No annulus‐like structure ase.g.inTetrahymenamucocysts andParameciumtrichocysts has been found in the membrane of these vesicles. The rosettes consist of 10‐nm particles and lack an outer ring. Vesicle membrane and plasma membrane appear to remain separated during exocytosis. In the course of lorica secretion, the number of rosettes continuously decreases, following an anterior‐posterior gradient. This indicates that new insertion of extrusive vesicles from intracellular stores occurs preferably at the anterior of t

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1989.tb00871.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

A method for induction of synchronous encystment in a hypotrichous ciliate,Paraurostylasp. is described. Cyst walls, isolated by shaking with glass beads, were analyzed by SDS‐polyacrylamide gel electrophoresis. To test optimal conditions of solubilization of cyst wall proteins, different treatments using Triton X‐100, EDTA, EGTA, urea, SDS and 2‐mercaptoethanol were carried out. At least, 15 different proteins were identified as specific to the cyst wall. Four low molecular weight polypeptides (40, 27–26, 20 and 18 kDa represented aproximately 70% of the cyst wall proteins. The 170, 135 and 40‐kDa bands exhibited a PAS‐positive reaction. Hydrogen and disulphide bonds were shown to be the most important interactions involving cyst wall proteins. Amino acid composition of cyst wall proteins was also investigated by HPLC. High amounts of glycine, cystine and proline we

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1989.tb00872.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Epithelial cell cultures derived from the ventral prostate of normal adult mice have been propagated in serum‐free medium. The cultures were initiated and maintained in Ham's F‐12 nutrient mixture supplemented with insulin (5 μg/ml), EGF (10 ng/ml), hydrocortisone (0.5 μg/ml), cholera toxin (10 ng/ml), bovine pituitary extract (25 μg protein/ml) and antibiotics. The cells exhibited microvilli on cell surfaces, interdigitations and junctional complexes including desmosomes between cells, and cytokeratins in cytoplasm which are characteristic of epithelial cells. In addition, the cells exhibited the tissue‐specific markers, prostatic acid phosphatase and prostate‐specif

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1989.tb00873.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

In the course of spermiogenesis in the mouse, spermatid cytoplasm contains numerous membrane pits, vesicles and membranous tubules which are frequently anastomosed. Pale and dense multivesicular bodies (MVB) and secondary lysosome‐like structures are also present in the cytoplasm. In order to study the pathway of non‐specific adsorptive endocytosis in spermatids, cationic ferritin (CF) was directly microinjected into the lumen of seminiferous tubules, and added to germinal cell culture. Tissue and cultures were fixed at various time intervals after injection.Two‐5 hr after microinjection of tracer, CF was found simultaneously in vesicles, tubules, MVB and in lysosome‐like bodies present in spermatids at all steps of spermiogenesis. Various membranous components of the Golgi medulla, and the innermost transsaccule of the Golgi cortex were labelled simultaneously. In primary cultures of spermatids, the vesicles contained the marker 5 min after its deposition; 10 min after deposition, CF was evident in tubules; at 30 min, CF was present in pale MVB; at 1 hr, the dense MVB and lysosome‐like bodies were labelled. Finally, at 2 hr 30 min, vesicles and tubules of the Golgi medulla contained CF grains.Apparently spermatids are very active cells in the process of adsorptive endocytosis throughout spermiogenesis. Endocytosis in spermatids is probably one of the mechanisms involved in the uptake of material used to build up spermatozoa components. The strong labelling of the Golgi region probably point to its role in recycling endocytosed

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1989.tb00874.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Liver peroxisomes during prenatal development were studied by means of morphological and morphometric analysis in foetuses growing both in untreated and in clofibrate‐treated rats. Pregnant rats were fed a standard diet (25 g/d) containing or not 0.8% clofibrate during the week preceding sacrifice and livers were excised from 13, 15, 17, 19 and 21‐day old foetuses and newborn rats. The morphometric analysis of hepatocyte peroxisomes, performed by a semiautomatic method in specimens incubated with 3,3′ diaminobenzidine, shows that the peroxisome volume density and average diameter in test animals were significantly increased over the control values. While the increase in the average diameter was roughly the same (×1.4) at all examined stages, the volume density increased over the control values particularly in foetuses over 19d‐old and in newborn rats; over the same period the peroxisome numerical density also significantly increased over the control values. Finally, the average diameters of peroxisome profiles in test rats showed a more dispersed distribution (SD 40%) than in control animals (SD 30%). These results demonstrate that clofibrate, given to rats during pregnancy, induces peroxisomal proliferation in the livers of their foetuses. Data are discussed in view of the models proposed for peroxisomal bi

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1989.tb00875.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

ADrosophila melanogastercell line devoid of centrioles has been recently described. In order to achieve an easier characterization of these acentriolar cells, we used the monoclonal antibody Bx 63 of M. Frusch which recognizes theDrosophilacentrosome. Although centrosomes are detected at every mitotic pole inDrosophilacells with centrioles, no such structure has been observed in 1182‐4 acentriolar cells. The antigenic material is, however, present in these cells. Moreover, we noticed a certain proportion of acentriolar cells in 4 other 1182 lines. The lack of centrioles previously found only in the 1182‐4 cells seems therefore not accidental and should be linked to their particular ori

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1989.tb00876.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Drosophilaembryos, because of their high proportion of dividing nuclei, offer many advantages for the study of the mitotic cycle. In the present study we combined immunofluorescence with interference contrast techniques to follow centrosome and spindle behavior in embryos exposed to diazepam during the first stages of development. Exposure to 100 μg/ml of diazepam produced polyploid and aneuploid figures resulting from the unusual fusion of one or more adjacent spindles. Diazepam also causes the inhibition of centrosome shifting and induces the formation of monopolar spindles during the metaphase‐anaphase transiti

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1989.tb00877.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY