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At least 523 records · Page 29Linked to original sources
PubMed2002

ACTIN2 is essential for bulge site selection and tip growth during root hair development of Arabidopsis.

Root hairs develop as long extensions from root epidermal cells. After the formation of an initial bulge at the distal end of the epidermal cell, the root hair structure elongates by tip growth. Because root hairs are not surrounded by other cells, root hair formation provides an excellent system for studying the highly complex process of plant cell growth. Pharmacological experiments with actin filament-interfering drugs have provided evidence that the actin cytoskeleton is an important factor in the establishment of cell polarity and in the maintenance of the tip growth machinery at the apex of the growing root hair. However, there has been no genetic evidence to directly support this assumption. We have isolated an Arabidopsis mutant, deformed root hairs 1 (der1), that is impaired in root hair development. The DER1 locus was cloned by map-based cloning and encodes ACTIN2 (ACT2), a major actin of the vegetative tissue. The three der1 alleles develop the mutant phenotype to different degrees and are all missense mutations, thus providing the means to study the effect of partially functional ACT2. The detailed characterization of the der1 phenotypes revealed that ACT2 is not only involved in root hair tip growth, but is also required for correct selection of the bulge site on the epidermal cell. Thus, the der1 mutants are useful tools to better understand the function of the actin cytoskeleton in the process of root hair formation.

Actins↗
PubMed2002

Genetic identification and genomic organization of factors affecting fruit texture.

Fleshy fruits are an essential part of the human diet providing vital vitamins, minerals and other health-promoting compounds. The texture of the ripe fruit has a significant effect on quality and influences consumer acceptance, shelf-life, resistance, and transportability. The development of rational approaches to improve texture and shelf-life depend on understanding the biological basis of fruit ripening. Until recently, work has focused on the isolation of ripening-related genes from a variety of fleshy fruits. However, little is known about the genes that regulate this complex developmental process or whether similar regulatory genes are active in all fruiting species. A major breakthrough would be the identification of generic genes associated with texture and other aspects of ripening in fleshy fruits. In tomato, a small number of single gene mutations exist, such as ripening-inhibitor (rin), non-ripening (nor), Never-ripe (Nr), and Colourless non-ripening (Cnr) which have pleiotropic effects resulting in the reduction or almost complete abolition of ripening. These mutations probably represent lesions in regulatory genes. The cloning of the wild-type alleles of RIN and NOR is reported by Moore et al. in this issue. This review focuses on the texture characteristics of the Cnr mutant. A possible framework for the molecular regulation of fruit texture is discussed and quantitative genetic approaches to determining the generic attributes of fruit texture are explored.

Cell Wall↗
PubMed1986

The zygotic mutant tailless affects the anterior and posterior ectodermal regions of the Drosophila embryo.

The recessive zygotic lethal mutation tailless maps to region 100A5,6-B1,2 at the tip of the right arm of chromosome 3, and results in shortened pharyngeal ridges in the head skeleton of the mature embryo and the elimination of the eighth abdominal segment and telson. Although they have a normal body length, tailless embryos have a smaller number of abdominal segments, some of which are larger than normal. The mutant phenotype is seen as early as 8 hr postfertilization, when tailless embryos are observed to have fewer tracheal pits than wildtype. At 9 hr, tailless embryos appear to be missing segments A8, A9, and A10 and have an abnormal clypeolabrum, optic lobes, and procephalic lobe. Segments A4, A5, A6, and A7 appear larger in tailless embryos than wildtype at this stage. The tailless mutation, although affecting anterior and posterior ectodermal structures in the mature embryo, does not affect the formation of pole cells, the posterior midgut, or the proctodeum, which arise from the most posterior region of the embryo. The mutation does result, however, in the failure of Malpighian tubule formation. Consistent with its effect on ectodermal segments, tailless leads to a reduction in the number of segmented, paired ganglia in the ventral nerve cord as well as to an abrupt alteration in the posterior region of the tracheal system. The role the tailless gene may play in the formation of the most anterior and posterior regions of the embryo's ectodermal body plan is discussed.

Acetylcholinesterase↗
PubMed2006

p27(Kip1) deficiency causes organ of Corti pathology and hearing loss.

p27(Kip1) (p27) has been shown to inhibit several cyclin-dependent kinase molecules and to play a central role in regulating entry into the cell cycle. Once hair cells in the cochlea are formed, p27 is expressed in non-sensory cells of the organ of Corti and prevents their re-entry into the cell cycle. In one line of p27 deficient mice (p27(-/-)), cell division in the organ of Corti continues past its normal embryonic time, leading to continual production of cells in the organ of Corti. Here we report on the structure and function of the inner ear in another line of p27 deficient mice originating from the Memorial Sloan-Kettering Cancer Center. The deficiency in p27 expression of these mice is incomplete, as they retain expression of amino acids 52-197. We determined that mice homozygote for this mutation had severe hearing loss and their organ of Corti exhibited an increase in the number of inner and outer hair cells. There also was a marked increase in the number of supporting cells, with severe pathologies in pillar cells. These data show similarities between this p27(Kip1) mutation and another, previously reported null allele of this gene, and suggest that reducing the inhibition on the cell cycle in the organ of Corti leads to pathology and dysfunction. Manipulations to regulate the time and place of p27 inhibition will be necessary for inducing functionally useful hair cell regeneration.

Animals↗
PubMed2005

Cellular invasion by Staphylococcus aureus reveals a functional link between focal adhesion kinase and cortactin in integrin-mediated internalisation.

Nosocomial infections by Staphylococcus aureus, a Gram-positive pathogen colonising human skin and mucosal surfaces, are an increasing health care problem. Clinical isolates almost invariably express fibronectin-binding proteins that, by indirectly linking the bacteria with host integrin alpha5beta1, can promote uptake of the microorganisms by eukaryotic cells. Integrin engagement by pathogenic fibronectin-binding S. aureus, but not by non-pathogenic S. carnosus, triggered the recruitment of focal contact-associated proteins vinculin, tensin, zyxin and FAK to the sites of bacterial attachment. Moreover, dominant-negative versions of FAK-blocked integrin-mediated internalisation and FAK-deficient cells were severely impaired in their ability to internalise S. aureus. Pathogen binding induced tyrosine phosphorylation of several host proteins associated with bacterial attachment sites, including FAK and the Src substrate cortactin. In FAK-deficient cells, local recruitment of cortactin still occurred, whereas the integrin- and Src-dependent tyrosine phosphorylation of cortactin was abolished. As siRNA-mediated gene silencing of cortactin or mutation of critical amino acid residues within cortactin interfered with uptake of S. aureus, our results reveal a novel functional connection between integrin engagement, FAK activation and Src-mediated cortactin phosphorylation. Cooperation between FAK, Src and cortactin in integrin-mediated internalisation of bacteria also suggests a molecular scenario of how engagement of integrins could be coupled to membrane endocytosis.

Actins↗
PubMed2005

ABERRANT PANICLE ORGANIZATION 1 temporally regulates meristem identity in rice.

We report a recessive mutation of rice, aberrant panicle organization 1 (apo1), which severely affects inflorescence architecture, floral organ identity, and leaf production rate. In the wild-type inflorescence, the main-axis meristem aborts after forming 10-12 primary branch primordia. However, in apo1, the main-axis meristem was converted to a spikelet meristem after producing a small number of branch primordia. In addition, the branch meristems in apo1 became spikelet meristems earlier than in wild type. Therefore, in the inflorescence, the apo1 mutation caused the precocious conversion of the meristem identity. In the apo1 flower, lodicules were increased at the expense of stamens, and carpels were formed indeterminately by the loss of meristem determinacy. Vegetative development is also affected in the apo1. Leaves were formed rapidly throughout the vegetative phase, indicating that APO1 is also involved in temporal regulation of leaf production. These phenotypes suggest that the APO1 plays an important role in the temporal regulation of both vegetative and reproductive development.

Cell Differentiation↗
PubMed2004

The phenotype of Arabidopsis ovule mutants mimics the morphology of primitive seed plants.

In seed plants, the ovule is the female reproductive structure, which surrounds and nourishes the gametophyte and embryo. This investigation describes the PRETTY FEW SEEDS2 (PFS2) locus, which regulates ovule patterning. The pfs2 mutant exhibited developmental defects in the maternal integuments and gametophyte. This mutation was inherited as a maternal trait, indicating that gametophyte defects resulted from ovule patterning aberrations. Specifically, the boundary between the chalaza and the nucellus, two regions of the ovule primordia, shifted towards the distal end of pfs2 ovule primordia. Results indicated that the PFS2 locus could: (i) be involved in the development of either the nucellus or the chalaza; or (ii) establish a boundary between these two regions. Examination of genetic interactions of the pfs2 mutation with other well-characterized ovule loci indicates that this locus affects integument morphogenesis. Interestingly, the pfs2 inner no outer and pfs2 strubbelig double mutants had inner integuments that appeared similar to their ancestral precursor. The fossil record indicates that the inner integument evolved by fusion of sterilized sporangia or branches around a central megasporangium. The question of whether the structures observed in these double mutants are homologous or merely analogous to the ancestral precursors of the inner integument is discussed.

Arabidopsis↗
PubMed2002

Entopically additive expression of GLABRA2 alters the frequency and spacing of trichome initiation.

GLABRA2 (GL2)/ATHB-10 encodes a homeodomain protein that belongs to the homeodomain-leucine zipper family. Mutant studies have revealed that this gene is involved in trichome, root-hair and seed-coat development. We used reverse genetics to investigate the role of GL2 in trichome development. A transgene consisting of a GL2-coding fragment preceded by the cauliflower mosaic virus 35S promoter (35S::GL2) did not complement defects in the gl2-1 mutant. In the wild-type genetic background, 35S::GL2 caused gl2-mutant-like and scarcely viable phenotypes, suggesting that ectopic overexpression of GL2 interrupts endogenous GL2 function in trichome development and is toxic to plants. On the other hand, another GL2 transgene containing the GL2 promoter (pGL2::GL2) complemented the gl2-1 mutation. Entopically additive expression of GL2 by introduction of pGL2::GL2 in the wild-type genetic background noticably increased the number of trichomes and induced production of adjacent trichomes. Consistent with this result, gl2-1/+ heterozygous leaves, whose GL2 expression was expected to decrease, had fewer trichomes than +/+ leaves. These results indicate that GL2 quantitatively regulates the frequency of trichome initiation and is involved in determining trichome spacing.

Arabidopsis↗
PubMed1990

Epicardial development in the axolotl, Ambystoma mexicanum.

Recent studies on avian and mammalian embryos have established that the epicardium is derived, not from the early heart tube, but from mesothelial tissue overlying the sinus venosus. We tested the validity of this concept for Amphibia by examining normal and cardiac lethal (c/c) mutant axolotl embryos (stages 35-43) by electron microscopy. In axolotl embryos, the myocardial surface of the heart remains exposed to the pericardial fluid through stage 39. At this stage the transverse septum releases into the pericardial cavity mesothelial cells that subsequently flatten over the adjacent ventricular myocardium. However, mesothelial cells observed on the developing epicardium always appear rounded and may extend a filopodium up to 75 microns. This apparent "substrate-dependent" difference in mesothelial cell shape may promote the extension of the epicardium over the rest of the myocardium. The initial site of epicardial formation persists in the adult as the ventricular pericardial stalk that connects the epicardium to the peritoneal lining of the transverse septum. Cardiac lethal (c/c) mutant embryos, despite the non-contractility of their myocardia, form their epicardia in the same way. This suggests that the c/c mutation does not impair those properties of the myocardium that render it a suitable substrate for epicardial spreading. The abnormal pattern of epicardial coverage of the edematous stage 41 c/c mutant heart could be the result of its abnormally large myocardial surface area, the abnormal proximity of the atrium to the transverse septum, and/or the absence of heart contractions which could aid the dispersion of mesothelial cells within the pericardial cavity. Despite species differences, epicardial development in the axolotl is similar to the general pattern described for higher vertebrate embryos.

Ambystoma↗
PubMed2002

KNAT1 and ERECTA regulate inflorescence architecture in Arabidopsis.

Plant architecture is dictated by morphogenetic factors that specify the number and symmetry of lateral organs as well as their positions relative to the primary axis. Mutants defective in the patterning of leaves and floral organs have provided new insights on the signaling pathways involved, but there is comparatively little information regarding aspects of the patterning of stems, which play a dominant role in architecture. To this end, we have characterized five alleles of the brevipedicellus mutant of Arabidopsis, which exhibits reduced internode and pedicel lengths, bends at nodes, and downward-oriented flowers and siliques. Bends in stems correlate with a loss of chlorenchyma tissue at the node adjacent to lateral organs and in the abaxial regions of pedicels. A stripe of achlorophyllous tissue extends basipetally from each node and is positioned over the vasculature that services the corresponding lateral organ. Map-based cloning and complementation studies revealed that a null mutation in the KNAT1 homeobox gene is responsible for these pleiotropic phenotypes. Our observation that wild-type Arabidopsis plants also downregulate chlorenchyma development adjacent to lateral organs leads us to propose that KNAT1 and ERECTA are required to restrict the action of an asymmetrically localized, vasculature-associated chlorenchyma repressor at the nodes. Our data indicate that it is feasible to alter the architecture of ornamental and crop plants by manipulating these genetically defined pathways.

Alleles↗
PubMed2003

Silencing the Drosophila ribosomal protein L14 gene using targeted RNA interference causes distinct somatic anomalies.

The Drosophila Minutes are haploinsufficient mutations that are defective in ribosomal protein (rp) production, resulting in short, thin bristles, delayed development and recessive lethality. In a Minute fly, the amount of rp gene messenger RNA (mRNA) is reduced to >or=50% of the normal amount of gene product, and becomes rate limiting for ribosome biogenesis, cell proliferation and growth. Haploinsufficiency increases the vulnerability to complete loss of gene function (homozygous null state) if hit by a second mutation. Because of the homozygous lethality, it has only been possible to study the effects of Minute mutations in heterozygous animals. To be able to study the consequences of a loss-of-function of an rp gene (0%>mRNA<50%) in developing and differentiated cells we used heritable RNA interference (RNAi) in combination with the yeast GAL4/UAS binary system to spatiotemporally knock down the ribosomal protein L14 (RpL14) gene. We show, at the RNA and phenotypic levels, that RNAi efficiently reduces RpL14 gene expression throughout development, causing lethality and distinct and dramatic somatic anomalies in both developing and differentiated cells.

Abnormalities, Multiple↗
PubMed1992

Olfactory physiology in the Drosophila antenna and maxillary palp: acj6 distinguishes two classes of odorant pathways.

This article provides characterization of the electrical response to odorants in the Drosophila antenna and provides physiological evidence that a second organ, the maxillary palp, also has olfactory function in Drosophila. The acj6 mutation, previously isolated by virtue of defective olfactory behavior, affects olfactory physiology in the maxillary palp as well as in the antenna. Interestingly, abnormal chemosensory jump 6 (acj6) reduces response in the maxillary palp to all odorants tested except benzaldehyde (odor of almond), as if response to benzaldehyde is mediated through a different type of odorant pathway from the other odorants. In other experiments, different parts of the antenna are shown to differ with respect to odorant sensitivity. Evidence is also provided that antennal response to odorants varies with age, and that odorants differ in their age dependence.

Animals↗
PubMed1994

Zea3: a pleiotropic mutation affecting cotyledon development, cytokinin resistance and carbon-nitrogen metabolism.

When photomorphogenesis takes place during early plant development, the cotyledons undergo a metabolic transition from heterotrophic sink metabolism to autotrophic source metabolism. A mutant screen was devised for seedlings affected in the regulation of nitrate assimilation during this early sink-source transition in Nicotiana plumbaginifolia. A mutant (EMS 203.6) was isolated for its inability to grow on low nitrate concentration. In contrast to wild-type (WT) plants, the mutant cotyledons remained tightly attached to each other throughout seedling development. It was found that a low carbon/nitrogen ratio (C/N ratio) in the medium was required for mutant growth. The higher the ratio was, the more the growth was inhibited. Mutant EMS 203.6 accumulated all amino acids in permissive conditions (low C/N ratio), and all amino acids and sugars also in selective (high C/N ratio) conditions. In addition, sucrose in the medium repressed light-regulated genes involved in nitrate assimilation and in photosynthesis in the mutant but not in the WT plants. The mutation was mapped to the Zea3 complementation group which confers resistance to zeatin. This zeatin resistance was associated with a hypertrophy of mutant cotyledons in response to cytokinin. Both cytokinin resistance and sensitivity to a high C/N ratio were not observed in etiolated mutant seedlings and were restricted to the jointed-cotyledon developmental stage. Previous physiological studies showed evidence for a role of cytokinins in the expression of nitrate reductase. Here, the first genetic evidence for a link between carbohydrate/nitrogen metabolism and cytokinin action during early development is provided.

Amino Acids↗
PubMed1987

A mutation affecting basal body duplication and cell shape in Paramecium.

The thermosensitive mutant sm19 of Paramecium tetraurelia undergoes a progressive reduction in cell length and basal body number over successive divisions at the nonpermissive temperature of 35 degrees C. In spite of these defects, sm19 cells retain the same generation time as wild-type cells at 35 degrees C. Cytological observations at both electron and light microscopy levels reveal no other perturbation than the rarefaction of basal bodies and the rare (3%) absence of one or two microtubules in basal bodies or ciliary axonemes. The temperature-sensitive period, during the last 30 min of the cell cycle, corresponds to the phase of basal body duplication. Upon transfer back to the permissive temperature, all basal bodies are normally duplicated. The mutational defect is transiently restored by microinjection of wild-type cytoplasm or of a soluble proteic fraction from wild-type cell homogenates. Altogether, the cytological and physiological data support the conclusion that the sm19+ gene codes for a diffusible product required for the initiation of basal body duplication and would thus be the first identified gene involved in this process. Our data also indicate that in Paramecium basal body number is not coupled with control of the cell cycle, but helps determine the shape of the cell via the organization of the cytoskeleton.

Animals↗
PubMed1994

Arabidopsis floral homeotic gene BELL (BEL1) controls ovule development through negative regulation of AGAMOUS gene (AG).

Ovules are the developmental precursors of seeds. In angiosperms the ovules are enclosed within the central floral organs, the carpels. We have identified a homeotic mutation in Arabidopsis, "bell" (bel1), which causes transformation of ovule integuments into carpels. In situ hybridization analysis shows that this mutation leads to increased expression of the carpel-determining homeotic gene AGAMOUS (AG) in the mutant ovules. Introduction of a constitutively expressed AG transgene into wild-type plants causes the ovules to resemble those of bel1 mutants. We propose that the BEL1 gene product directs normal integument development, in part by suppressing AG expression in this structure. Our results allow expansion of the current model of floral organ identity to include regulation of ovule integument identity.

Arabidopsis↗
PubMed1998

Analysis of a Drosophila cyclin E hypomorphic mutation suggests a novel role for cyclin E in cell proliferation control during eye imaginal disc development.

We have generated and characterized a Drosophila cyclin E hypomorphic mutation, DmcycEJP, that is homozygous viable and fertile, but results in adults with rough eyes. The mutation arose from an internal deletion of an existing P[w+lacZ] element inserted 14 kb upstream of the transcription start site of the DmcycE zygotic mRNA. The presence of this deleted P element, but not the P[w+lacZ] element from which it was derived, leads to a decreased level of DmcycE expression during eye imaginal disc development. Eye imaginal discs from DmcycEJP larvae contain fewer S phase cells, both anterior and posterior to the morphogenetic furrow. This results in adults with small rough eyes, largely due to insufficient numbers of pigment cells. Altering the dosage of the Drosophila cdk2 homolog, cdc2c, retinoblastoma, or p21(CIP1) homolog dacapo, which encode proteins known to physically interact with Cyclin E, modified the DmcycEJP rough eye phenotype as expected. Decreasing the dosage of the S phase transcription factor gene, dE2F, enhanced the DmcycEJP rough eye phenotype. Surprisingly, mutations in G2/M phase regulators cyclin A and string (cdc25), but not cyclin B1, B3, or cdc2, enhanced the DmcycEJP phenotype without affecting the number of cells entering S phase, but by decreasing the number of cells entering mitosis. Our analysis establishes the DmcycEJP allele as an excellent resource for searching for novel cyclin E genetic interactors. In addition, this analysis has identified cyclin A and string as DmcycEJP interactors, suggesting a novel role for cyclin E in the regulation of Cyclin A and String function during eye development.

Alleles↗
PubMed2006

Plastidial phosphorylase is required for normal starch synthesis in Chlamydomonas reinhardtii.

Among the three distinct starch phosphorylase activities detected in Chlamydomonas reinhardtii, two distinct plastidial enzymes (PhoA and PhoB) are documented while a single extraplastidial form (PhoC) displays a higher affinity for glycogen as in vascular plants. The two plastidial phosphorylases are shown to function as homodimers containing two 91-kDa (PhoA) subunits and two 110-kDa (PhoB) subunits. Both lack the typical 80-amino-acid insertion found in the higher plant plastidial forms. PhoB is exquisitely sensitive to inhibition by ADP-glucose and has a low affinity for malto-oligosaccharides. PhoA is more similar to the higher plant plastidial phosphorylases: it is moderately sensitive to ADP-glucose inhibition and has a high affinity for unbranched malto-oligosaccharides. Molecular analysis establishes that STA4 encodes PhoB. Chlamydomonas reinhardtii strains carrying mutations at the STA4 locus display a significant decrease in amounts of starch during storage that correlates with the accumulation of abnormally shaped granules containing a modified amylopectin structure and a high amylose content. The wild-type phenotype could be rescued by reintroduction of the cloned wild-type genomic DNA, thereby demonstrating the involvement of phosphorylase in storage starch synthesis.

Algal Proteins↗
PubMed2002

Intimin type influences the site of human intestinal mucosal colonisation by enterohaemorrhagic Escherichia coli O157:H7.

BACKGROUND: Enterohaemorrhagic (EHEC) and enteropathogenic (EPEC) Escherichia coli epithelial cell adhesion is characterised by intimate attachment, and attaching and effacing (A/E) lesion formation. This event is mediated in part by intimin binding to another bacterial protein, Tir (translocated intimin receptor), which is exported by the bacteria and integrated into the host cell plasma membrane. Importantly, EPEC (O127:H6) and EHEC (O157:H7) express antigenically distinct intimin types known as intimin alpha and gamma, respectively. EHEC (O157:H7) colonises human intestinal explants although adhesion is restricted to the follicle associated epithelium of Peyer's patches. This phenotype is also observed with EPEC O127:H6 engineered to express EHEC intimin gamma. AIMS: To investigate the influence of intimin on colonisation of human intestine by E coli O157:H7, and intimin types on tissue tropism in humans. METHODS: Human intestinal in vitro organ culture with wild type and mutant strains of O157:H7 were employed. RESULTS: Introducing a deletion mutation in the eae gene encoding intimin gamma in EHEC (O157:H7) caused the strain (ICC170) to fail to colonise human intestinal explants. However, colonisation of Peyer's patches and A/E lesion formation were restored with intimin gamma expression from a plasmid (ICC170 (pICC55)). In contrast, complementing the mutation with intimin alpha resulted in a strain (ICC170 (pCVD438)) capable of colonising and producing A/E lesions on both Peyer's patch and other small intestinal explants. CONCLUSION: Intimin is necessary for human intestinal mucosal colonisation by E coli O157:H7. Intimin type influences the site of colonisation in a Tir type independent mechanism; intimin gamma appears to restrict colonisation to human follicle associated epithelium.

Adhesins, Bacterial↗