摘要:

AbstractThe one form of cytoplasmic inheritance that has not been assimilated into the Central Dogma is the inheritance of surface structural patterns, a phenomenon most clearly expressed in cilates. Vance Tartar, although he worked with a genetically undomesticated organism (Stentor coeruleus), provided early evidence for the crucial role of clonally propagated features of the cell cortex. He showed that the capacity for development of cortical organelle systems is associated with a particular relational feature, the “locus of stripe contrast” (LSC), and that clonally inherited cortical variants (homopolar doublets) could be created at will by microsurgical operations that duplicated the LSC. Tartar also hoped to demonstrate the existence of what David Nanney called “cellular architects” by provoking stentors to carry out entirely novel types of morphogenetic performances. He eventually acknowledged failure, although the bizarre juxtapositions by which he attempted to elicit such novel performances did bring about specific and illuminating defects in cortical development. Subsequent analyses of similar defects in other ciliates revealed not the unitary “pattern factor” postulated by Tartar, but rather a hierarchy of distinct patterning mechanisms. Nonetheless, by pursuing an embryological approach toward morphogenesis in a highly regulative ciliate, Tartar uncovered relational aspects of pattern‐determination; this, in my view, delineates the major problem that we must solve to gain understanding of intracellular patterning. © 1992 W

ISSN:0192-253X    

DOI:10.1002/dvg.1020130302

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractThe present study reveals a deficiency in the number of ciliated basal bodies along 180° rotated ciliary rows (IRs) inTetrahymena. This feature is common to IRs recently generated in young clones with stable corticotypes (total number of ciliary rows per cell), irrespective of the number of IRs present per cell or their cellular location, and is found before the cell loses any of the IRs. In cells bearing three IRs, the IRs on the two sides of the inversion immediately next to normal ciliary rows (junctures) exhibit an even greater deficiency in ciliated basal bodies, compared to the IR located internally between two other IRs; the normal ciliary rows flanking the inversion are also somewhat deficient. These observations show that the IRs ofTetrahymenaare structurally deficient, hence developmentally defective, and suggest that they are intrinsically unstable. We propose that basal body development along IRs tends to be truncated before the stage of ciliation; such basal bodies would fail to acquire the potential to serve as nucleating centers for new basal body development in the next round of basal body proliferation, leading to the eventual loss of the IRs. © 1992 Wiley‐Liss,

ISSN:0192-253X    

DOI:10.1002/dvg.1020130303

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractThe long‐known teratogenic effects (dorsalisation) of lithium on amphibian embryos has recently raised renewed interest. As it is known that lithium blocks the polyphosphoinositide (PI) cycle, causing a depressed level ofmyo‐inositol, and as injections ofmyo‐inostiol have been shown to rescue the effects of Li+, it was postulated that Li+causes a flattening of gradients of PI cycle activity underlying the developmental polarities. We have studied the effect of Li+on the morphogenesis of the unicellular organism,Paramecium.We show (1) that exposure to 25 mM Li+during division yields precise distorsions of the cortical pattern that can be explained by a uniformisation of surface growth i.e. partial suppression of the right/left and antero/posterior asymmetries and (2) that Li+effects are rescued by injection ofmyo‐ inositol. These results suggest that spatially graded activity of the PI cycle (ensuring in turn a spatially graded distribution of secondary messengers directly involved in the morphogenetic processes) appeared early in evolution. © 1992 Wiley

ISSN:0192-253X    

DOI:10.1002/dvg.1020130304

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractThe number and length of oral membranelles were determined for both large and smallStentorfrom well‐fed, growing cultures and nutrient‐deprived cultures, respectively. Small cells possess both significantly fewer and shorter membranelles than do large cells. For both large and small cells, each membranelle is composed of three rows of basal bodies. The membranelles closest to the gullet have a third row that is only slightly shorter than the other two. The third row becomes rapidly shorter as membranelles become increasingly distant from the gullet. A short distance from the gullet, and for the remainder of the band, the third row is composed ofonly one to four basal bodies. The first two rows consist of approximately 35 basal bodies each in large cells and approximately 26 basal bodies each in small cells. This indicates thatStentorregulates the number of basal bodies per row, but not the number of rows, in response to changes in cell size. © 1992 Wiley‐Lis

ISSN:0192-253X    

DOI:10.1002/dvg.1020130305

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractUnderstanding the mechanism that determines the cell division plane is one of the most important problems in the fields of cell and developmental biology. Studying the timing and site of formation of contractile ring (CR) micro‐filaments provides key information for solving the problem. We tried to create a nonfunctional CR inTetrahymenaby microinjecting rabbit skeletal muscle actin, which can copolymerize withTetrahymenaactin but has properties different from those ofTetrahymenaactin. When skeletal muscle actin was injected in a predivision stage, before the onset of furrow constriction, long‐term arrest of cell division was observed. Muscle actin did not cause any delay in cell division when the actin was injected at any stage other than the predivision stage. In all cases, muscle actin had little affect on other actin‐related functions. Injected skeletal muscle actin polymerized near the equatorial division plane in cases of cell division arrest; it polymerized at other nonspecific locations when cell division was observed. Arrest occurred when the microinjection took place in the 17‐min period just before the start of furrowing. This period coincides with the occurrence of equatorial deposits of p85, which is also suggested to be required for the determination of the division plane. The present experimental results are consistent with the idea that p85 is a crucial factor for determining the cell division plane and also functions as a polymerization nucleus for CR microfilaments. © 1992 Wiley

ISSN:0192-253X    

DOI:10.1002/dvg.1020130306

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractDuring cytokinesis, furrowing creates new boundaries for daughter cells. Following a shift to a restrictive temperature, cells of the temperature‐sensitive cell‐division‐arrest (cdaA1) mutant ofTetrahymena thermophilacomplete development of the oral apparatus for the prospective posterior daughter cell before becoming arrested in cytokinesis. When maintained under weak restrictive conditions (35°C), some of the chains were arrested prior to the start of fission line formation (D‐shaped chains), whereas others manifestedrudimentary unilateral furrowingon the ventral side (B‐shaped chains). In their second cell cycle following the temperature shift, the D‐shaped chains usually formed onlyoneoral primordium, at a position highly correlated with the length of the entire chain. The B‐shaped chains always producedtwoseparate oral primordia, located at irregular positions anterior and posterior to the division furrow, often close to the posterior oral apparatus produced during the first cycle. These results suggest that the formation of the fission line sets a reference boundary to assess the number of oral primordia and influence their position, that appear during subsequent morphogenetic episodes. They also indicate that, during cell division cycles, pre‐existing oral apparatuses do not strongly inhibit the formation of new oral apparatuses in their close vicinity. © 199

ISSN:0192-253X    

DOI:10.1002/dvg.1020130307

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractParamecium caudatumloses the ability to form food vacuoles at the crescent stage of the micronucleus from 5 to 6 hr after the initiation of conjugation and regains it immediately after the third division of the zygotic nucleus. To assess the micronuclear function in the development of the oral apparatus after coniugation, prezygotic micronuclei was removed from cells at various stages of conjugation, and their ability to form food vacuoles were examined. (1) When all of the prezygotic micronuclear derivatives were eliminated before the stage of formation of the zygotic nucleus, the exconjugant did not regain its ability. (2) When a zygotic nucleus or postzygotic nuclei were removed, in some cases the cell formed as many food vacuoles as did nonoperated cells after conjugation, while in other operated cells the number of food vacuoles was subnormal. (3) When a micronucleus from a cell at vegetative phase (G1) was transplanted into a cell of an amicronucleate mating pair at the stage between 8 and 9 hr after the initiation of conjugation, the implanted cell regained the ability to form food vacuoles. However, no cell regained the ability when the implantation was carried out within 1 hr after the separation of the mates. The results show that the micronucleus plays an indispensable role in the development of the oral apparatus at the stages of exchange of gametic nuclei and fertilization and that the micronucleus transplanted from asexual cells can fulfill this function. On the other hand, removal of the macronucleus from exconjugants showed that the maternal macronucleus also has an indispensable function in regaining the ability to form food Vacuoles. © 1992 Wiley‐Liss, I

ISSN:0192-253X    

DOI:10.1002/dvg.1020130308

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractThis study examines the timing of micronuclear mitosis during the vegetative cell cycle and shows that mitosis begins early in the division process and coincides approximately with the earliest stages of oral morphogenesis (about 0.6 in the cell cycle in synchronous cell samples). Thecc1mutation blocks cell cycle progression prior to the point of commitment to division. Although thecc1mutation blocks macronuclear DNA synthesis under restrictive conditions, it does not block micronuclear DNA synthesis. However, absence of functionalcc1gene product leads to blockage of micronuclear mitosis prior to completion of anaphase. This point coincides with commitment to division and is also the point at which oral morphogenesis is blocked incc1cells. The tim‐ings of the transition points for micronuclear mitosis and oral morphogenesis incc1cells are closely associated in both synchronous cell samples and in asynchronous cultures. © 1992 Wiley‐Liss,

ISSN:0192-253X    

DOI:10.1002/dvg.1020130309

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractWe have constructed a laser optical force trap (“laser tweezers”) by coupling an Nd:YAG laser to an optical microscope with a high numerical aperture objective. The laser beam (approximately 0.1 W power) is focused to a diffraction‐limited spot at the specimen plane of the objective: the wavelength chosen (1,064 nm) is not strongly absorbed by most biological materials and is thus not ablative. Because the intensity of the laser beam increases towards the center of the focal spot, small particles brought near the spot will be attracted to the center and held there. Movement of the laser beam will tend to move any trapped particles with it. The laser tweezers can permit precise, nondestructive repositioning of small structures inside a living cell, without recourse to micromanipulators. Initial work has involved the use of laser tweezers on cells ofParamecium tet‐raureliaheld by a rotocompressor. We have been able to trap and reposition small organelles, especially the highly refractile structures known as crystals. Using a trapped crystal as a “tool”, we have been able to push micronuclei and other structures for many micrometers to virtually any desired location in a cell. In spite of extended exposure of specific structures and of individual cells to the laser beam, no damage has been detectible. Exposed cells, which were removed from the rotocompres‐sor and cultured, showed complete viabilty. The laser tweezers technique shows tremendous potential for applications to the study of many fundamental cellular and developmental phenomena in paramecia and other ciliates. For example, we intend to use this technique to investigate temporal and spatial characteristics of nuclear determining regions during sexual reorganization inParamecium. © 1992 W

ISSN:0192-253X    

DOI:10.1002/dvg.1020130310

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractA morphogenetically active substance released by the predatory ciliateLem‐badion bullinumis recognized by ciliates of the genusEuplotes, which are potential prey organisms ofLembadion.The substance (L‐factor) induces cells of the genusEuplotesto become less compact, which reduces their likelihood of becoming engulfed. Under the influence of thisLembadion‐derived signal,E. octocarinatusdevelops extended wings and dorsal and ventral ridges and transforms within a few hours from its typical ovoid morph into an enlarged circular morph. This takes place without cell division. We have isolated the L‐factor and report that it is a protein with a mass of 31,500 Da. The factor has been purified to chromatographic and electrophoretic homogeneity and was found to be active at concentrations as low as 10−12mol/L. © 1992 Wiley

ISSN:0192-253X    

DOI:10.1002/dvg.1020130311

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY