Wing reduction and cell death in Drosophila hydei: Analysis of the mutants Notch and Costal-nick

Cell death and its effect on wing size have been described in some wing mutants of Drosophila hydei. Dead cells in the imaginal discs were localized by Nile-bule and acridine-orange staining. Various Notch (N) alleles, the mutation Costal-nick (Cnk) and the compound N/Cnk show characteristic patterns of cell death in the imaginal wing disc. Some but not all of the structural features of the adult wing can be related to the site of cell death during larval stages. In N^Ax types, extensive cell death is followed by regenerative growth, invalidating a simple relation between size of the disk and size of the wing. In N^ts/Cnk cell death and wing morphology depend on the breeding temperature. From temperature experiments we conclude that cell death starts between day 4 and 5 after egg laying and can be induced by a shift to the restrictive temperature during the critical phase. Patterns of wing incisions and cell death in N^ts/Cnk genotypes seem not to be delimited by any of the known compartment boundaries.     

Tubulin and FtsZ structures: functional and therapeutic implications

The microtubule cytoskeleton has lagged nearly a decade behind the actin cytoskeleton with respect to structural information on the basic polymer subunit. This structural inferiority complex has finally been lifted by two recent papers describing the structures of the αβ tubulin dimer⁽¹⁾ and FtsZ,⁽²⁾ a protein similar to tubulin that is essential for cell division in prokaryotes. BioEssays 20 :523–527, 1998. © 1998 John Wiley & Sons Inc.     

Haltere determination and mutations at the bithorax locus

Mutations at the bithorax locus transform anterior haltere tissue into anterior wing. These transformations could in principle be due to the mutations altering either the expression or cell heredity functions of determination. I have studied two alleles of the bithorax locus bx³ and bx^34e using disc culture techniques and found that both produce their transformations by altering the expression of the determined state. I have also found that the expression of the temperature-sensitive allele, bx^34e, can be altered by temperature shifts during the culture period. Evidence has been obtained that suggests that such changes in expression do not require growth or cell division.     

Mutations in cell division proteins FtsZ and FtsA inhibit φX174 protein-E-mediated lysis of Escherichia coli

Electron microscopic studies emphasized that the protein-E-specific transmembrane tunnel structure, which permeabilizes Escherichia coli, is not randomly distributed over the cell envelope but is restricted to areas of potential division sites. These sites were located predominantly in the middle of the cell, but approximately one-third of these structures are found at the polar sites. Therefore, E. coli mutant strains with defects in cell division components were tested for their sensitivity to protein-E-mediated lysis. The ftsZ84 and the ftsA12 cell division mutant strains of E. coli were tolerant to protein-E-mediated lysis, whereas the ftsA3 mutant strain was lysed by protein E under conditions nonpermissive for division. The protein-E-tolerant phenotype of ftsZ84 and ftsA12 and the lysis-sensitive phenotype of other components of the septosome (e.g., ftsA3, ftsQ, and ftsI) suggest that initiation of cell division – rather than specific functions of cell division – plays an essential role in protein-E-mediated lysis. SulA-overproducing cells had a lysis-positive phenotype, the ring structure – but not the GTPase function - of FtsZ was impaired. Received: 14 April 1998 / Accepted: 9 June 1998     

COMPARATIVE PHYSIOLOGICAL STUDY OF MARINE DIATOMS AND DINOFLAGELLATES IN RELATION TO IRRADIANCE AND CELL SIZE. I. GROWTH UNDER CONTINUOUS LIGHT1,2

Cell division rates and chlorophyll a and protein contents for ten diatom and dinoflagellate species were measured. Species were chosen to include a wide range of cell size in terms of both cell volume and cell protein: from 0.004 ng protein/cell for a small Chaetoceros sp. to 2.2 ng protein/cell for Prorocentrum micans Ehrenberg. Experiments were conducted in batch or semi-continuous cultures at 21 C under continuous illumination from 8–256 μEin ^.m^-2'^.s^-1. Light saturation of cell division occurred at 32–80 μEin m^-1 s^-1 for all species, with no observable difference between the two phylogenetic groups. When the light-saturated cell division rates were plotted against cell size as protein/cell, the diatoms and dinoflagellates fell on two separate lines with the diatoms having higher rates. Chl a /protein ratios (μg/μg) decreased with increasing irradiance. The diatoms had higher chl a per unit protein. The relationship between cell division rate and the chl a/protein ratio is discussed.     

scalloped functions in a regulatory loop with vestigial and wingless to pattern the Drosophila wing

 The development of the Drosophila wing involves progressive patterning events. In the second larval instar, cells of the wing disc are allotted wing or notum fates by a wingless-mediated process and dorsal or ventral fates by the action of apterous and wingless. Notch-mediated signalling is required for the expression of the genes vestigial and scalloped in the presumptive wing blade. Later, wingless, Notch and cut are involved in cell fate specification along the wing margin. The function of scalloped in this process is not well understood and is the focus of this study. We show that patterning downstream of Notch and wingless pathways is altered in scalloped mutants. Reduction in scalloped expression results in a loss of expression of wing blade- and margin-specific markers. Misexpression of scalloped in the presumptive wing causes misexpression of scalloped, vestigial and wingless reporter genes. However, high levels of scalloped expression have a negative influence on wingless, vestigial and its own expression. Our results demonstrate that scalloped functions in a level-dependent manner in the presumptive wing blade in a loop that involves vestigial and itself. We suggest that wing development requires the regulated expression of scalloped together with vestigial–the ”wing formation” effects of Vestigial in other imaginal discs are probably due to its interaction with the scalloped gene product normally expressed in these discs. Received: 6 May 1998 / Accepted: 22 July 1998     

Multiple Allelism of the net Gene in Drosophila melanogaster and Drosophila simulans

Thenetgene mutations are known to cause abnormal pattern of veining in all wing regions except for the first posterior cells. In natural populations of Drosophila melanogaster, the net alleles were identified, which differ in phenotypic expression from standard mutations. The mutants net-extra-analis from a population Belokurikha-2000 have only a single additional vein in the third posterior cell. A line from Chernobyl-1986 population have another nontypical allele net ^Ch86 and shows a lower degree of abnormalities than that usually observed. About 10% of these flies have an additional vein fragment in the first posterior cell. In both males and females ofD. simulans population Tashkent -2001, which exhibit net ^ST91 mutation, a net of additional veins is formed as a specific additional fragment in the first posterior cell. The pattern of veining conferred by alleles net-extra-analis and net ^Ch86 is altered to a lesser extent; these alleles are dominant with respect to alleles net ^2-45 and net ^ST91, which cause more abnormalities. The heterozygotes for alleles net ^ST9 and net ^Ch86 and for Df(2) net ⁶² deletion have an additional fragment in the first posterior cell and show similarly strong deviations from normal wing vein pattern. The naturalnet alleles correspond, presumably, to different molecular gene defects involved into uncertain local interactions with numerous modifying factors and other genes that specify the wing vein pattern.     

Cell division and the stability of cellular populations

 This paper couples a general d-dimensional (d arbitrary) model for the intracellular biochemistry of a generic cell with a probabilistic division hypothesis and examines the consequence of division for stability of cell function and structure. We show rather surprisingly that cell division is capable of giving rise to a stable population of cells with respect to function and structure even if, in the absence of cell division, the underlying biochemical dynamics are unstable. In the context of a simple example, our stability condition suggests that rapid cell proliferation plays a stabilizing role for cellular populations. Received: 15 January 1996 / Revised version: 31 July 1998     

Activity of membrane ATPase during inhibition and reversion ofEscherichia coli cell division

Activity of Mg²⁺-dependent ATPase from the fraction of cell-free homogenate sedimenting at 35 000×g was studied during the growth and division ofEscherichia coli B. It decreased with the transition to stationary growth phase and after a specific inhibition of cell division. During the reversion of the division of filamentous forms the activity sharply increased; with the end of the reversion it dropped again to the level prior to the inhibition. The possible connection of the activity of Mg²⁺-dependent ATPase with the cell division ofEscherichia coli B is discussed.     

Cell division of the Escherichia coli lon- mutant

Summary Escherichia coli lon ^-cells were subjected to treatments which produced a decrease in the DNA/mass ratio of the cell. Thymine starvation, a shift-up from minimal medium to rich medium, and exposure to BUdR each caused greater inhibition of cell division in lon ^-cells than in lon ⁺cells. DNA metabolism was found to be the same in both lon ⁺and lon ^-cells during these treatments. The results are consistent with the hypothesis that the lon ^-defect leads to inhibition of cell division under conditions which produce a decreased DNA/mass ratio.     

The primitive red algae Cyanidium caldarium and Cyanidioschyzon merolae as model system for investigating the dividing apparatus of mitochondria and plastids

The Cyanidiophyceae species Cyanidium caldarium and Cyanidioschyzon merolae have played important roles in showing the division mechanisms of mitochondria and plastids. The apparatus regulating mitochondrial and plastid divisions was formerly unknown. We first identified the division apparatus of plastids, called the plastid-dividing ring (PD ring), in C. caldarium and the division apparatus of mitochondria, called the mitochondrion-dividing ring (MD ring), in C. merolae. Eukaryotic cell division is therefore controlled by at least three dividing apparati (rings)—a contractile ring, an MD ring, and a PD ring—while bacterial division is controlled by a single bacterial contractile FtsZ ring. BioEssays 20 :344-354, 1998.© 1998 John Wiley & Sons, Inc.     

Brassinolide affects the rate of cell division in isolated leaf protoplasts of Petunia hybrida

Brassinosteroids are known to promote cell elongation in a wide range of plant species but their effect on cell division has not been as extensively studied. We examined the effect of brassinolide on the kinetics and final division frequencies of regenerating leaf mesophyll protoplasts of Petunia hybrida Vilm v. Comanche. Under optimal auxin and cytokinin conditions, 10–100 nM brassinolide accelerated the time of first cell division by 12 h but had little effect on the final division frequencies after 72–120 h of culture. One micromolar brassinolide showed the same acceleration of first cell division but inhibited the final division frequency by approximately 20%. Under sub-optimal auxin conditions, 10–100 nM brassinolide both accelerated the time of first cell division and dramatically increased the 72- to 120-h final division frequencies. Isolated protoplasts may provide a useful model system to investigate the molecular mechanisms of brassinosteroid action on cell proliferation. Received: 1 December 1997 / Revision received: 13 February 1998 / Accepted: 24 April 1998     

DNA SYNTHESIS,CELL DIVISION,AND CELL DIFFERENTIATION DURING LEAF DEVELOPMENT OF XANTHIUM PENNSYLVANICUM

Leaf growth consists of two basic processes, cell division and cell enlargement. DNA synthesis is an integral part of cell division and can be studied with autoradiographic techniques and incorporation of some labeled precursor. Studies were made on the synthesis of nuclear DNA through incorporation of ³H-thymidine in various parts of the lamina during the entire course of leaf development of Xanthium pennsylvanicum. The time course analysis of DNA synthesis was correlated with cell division and rates of cell enlargement. Significant differences in ³H-thymidine incorporation were found in various parts of the lamina. Cell division and DNA synthesis were highest in the early stages of development. Since no ³H-thymidine was incorporated after cessation of cell division (LPI 2.8) in the leaf lamina, it appears that DNA synthesis is not needed for enlargement and differentiation of Xanthium cells. Rates of cell enlargement were negligible in the early development and reached their maximum after cessation of mitoses, between plastochron ages (LPI) 3 and 4. Cells matured between LPI's 5 and 6. Enzymatic activity was correlated with cell division and cell differentiation at various stages of leaf development.     

Differential mitotic rates and patterns of growth in compartments in the Drosophila wing

In the wing disks of Drosophila slowly dividing cells of Minute mutations are progressively eliminated from Minute/Minute⁺ mosaic compartments by a process known as cell competition. From a study of two different Minutes we show here that the intensity of competition is greater in the more extreme Minute with the slowest rate of cell division. The way in which the more rapidly growing Minute⁺ clones grow and overcome the surrounding Minute cells is described and cell competition is shown to be a result of local interactions between slow- and faster-growing cells.     

Cell degeneration and elimination in the imaginal wing disc,caused by the mutationsvestigial andUltravestigial ofDrosophila melanogaster

Summary The mutationsvestigial (vg; recessive) andUltravestigial (vg ^U; dominant) ofDrosophila melanogaster give rise to identical mutant adult phenotypes in which much of the cases this results from cell death in the presumptive wing margin of the wing disc in the third larval instar, but the process of cell degeneration is quite different in the two mutants. Invg cell death occurs continuously throughout the third larval instar, while invg ^U it occurs only in the early third instar. Cells fragment and some of the fragments condense, becoming electron dense (apoptosis). Both condensed and ultrastructurally normal cell fragments are extruded to the basal side of thevg disc epithelium. They accumulate under the basal lamina in the wing pouch area until they are phagocytosed by blood cells entering the wing pouch during the six hours following pupariation. Fragments are not extruded from thevg ^U epithelium but are apparently phagocytosed by neighboring epithelial cells. The basal lamina undergoes mophological changes following pupariation and is phagocytosed by blood cells in both wild-type andvestigial, but investigial the degenerated cell fragments are also engulfed by the same blood cells.     

Effect of 12C+5 ion beam irradiation on cell viability and plant regeneration in callus,protoplasts and cell suspensions of Lavatera thuringiaca

Summary The biological effects of irradiation with¹²C⁺⁵ ion beam on plant cells have been analyzed. Protoplasts and cell suspensions ofLavatera thuringiaca, and a somatic hybrid callus (Hibiscus rosa-sinensis +Lavatera thuringiaca), were irradiated with doses from 0.05 to 50 Gy, and the effects on cell growth, cell division, cell viability and embryogenesis rates were analyzed. Irradiation with¹²C⁺⁵ ion beam at relatively very low doses (5.0 Gy) significantly inhibited cell division, yet the survival rate and regeneration capability of the cells through somatic embryogenesis were conserved in more than 70 and 50 %, respectively. These results indicate that cell division is the most sensitive parameter to irradiation, accounting for the inhibition of colony formation and callus growth. The potential use of the¹²C⁺⁵ ion beam in asymmetric protoplast fusion experiments is discussed.     

Action of the cubitus interruptus-wallace mutant in Drosophila melanogaster: A study of leg morphology on mosaic and haplo-4 flies

The fourth chromosome mutant cubitus interruptus-Wallace(ci^W) produces leg, wing, and body bristle aberrations. The effect on the wing is similar to that produced by cubitus interruptus-dominant (ci^D) which also has an influence on larval segmentation indicating that it has a regulatory function. Leg morphology of haplo-4, ci^W, and mosaic haplo-4:diplo-4, ci/ci⁺ flies was examined in an attempt to distinguish between a structural and a regulatory function by ci^W. Aberrations recovered include failure of segment elongation, intersegmental gaps, duplication of bristles, and segments that are shorter than normal and of greater than normal diameter. Many of these effects are localized, suggesting that ci^W may act to maintain cell positional reference. Increased local cell proliferation appears to be one manifestation of loss of the normal function.     

The role of asymmetric cell division in pteridophyte cell differentiation. I. Localized metal accumulation and differentiation inVittaria gemmae andOnoclea prothallia

Summary In gemmae ofVittaria graminifolia and prothallia ofOnoclea sensibilis, cell differentiation is initiated by nuclear migration and geometrically asymmetric cell division. The small daughter cells inVittaria develop into antheridia in the presence of gibberellic acid or into rhizoids or new prothallia in its absence. Antheridial differentiation from asymmetric division is induced inOnoclea byPteridium antheridiogen, whereas rhizoid or vegetative cell formation occurs in its absence. Although asymmetric cytokinesis initiates differentiation, it does not in itself determine the developmental fate of the smaller cell. Several histochemical techniques demonstrate that prior to nuclear migration and cell division, Ca²⁺ accumulates in the cytoplasm and wall of the cell at the site where asymmetric division will occur, regardless of the developmental fate of the small cell. The cytoplasmic localization of Ca²⁺ appears to reflect a mobilization of Ca²⁺ from within the cell that eventually moves into the cell wall. We propose that this internal accumulation of Ca²⁺ leads to a localized decrease in cytosolic [Ca²⁺] which in turn may regulate developmental events such as nuclear migration.Publishing prior to 1984 as Alix R. Bassel.     

Induction of only limited elongation instead of filamentation by inhibition of cell division in Corynebacterium glutamicum

In order to characterize the cell-division mechanism of coryneform bacteria, we tried to isolate cell-division mutants from Corynebacterium glutamicum after N-methyl-N'-nitro-N-nitrosoguanidine mutagenesis, such as Escherichia coli fts mutants, which form long filaments at the restrictive temperatures. At the non-permissive temperature, most of the mutants formed club-shaped or dumbbell-shaped, elongated rod cells, but no filament formers were isolated. Then we examined the effects of cell division inhibitors on this organism. Cephalexin and sparfloxacin, which are the inhibitors of septation and DNA synthesis respectively, and are known to cause cell filamentation in E. coli, did not cause filamentation in C. glutamicum but induced morphological changes that were similar to those observed with the temperature-sensitive ts mutants of C.␣glutamicum. These results suggest that C. glutamicum has a unique regulation mechanism, that is, the inhibition of cell division leads to cessation of cell elongation. Received: 5 February 1998 / Received revision: 6 April 1998 / Accepted: 27 April 1998