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E Coen

Publications and source records attributed to E Coen.

At least 19 recordsLinked to original sources
PubMed2001

Ancient asymmetries in the evolution of flowers.

Dorsoventral asymmetry in flowers is thought to have evolved many times independently as a specialized adaptation to animal pollinators. To understand how such a complex trait could have arisen repeatedly, we have compared the expression of a gene controlling dorsoventral asymmetry in Antirrhinum with its counterpart in Arabidopsis, a distantly related species with radially symmetrical flowers. We found that the Arabidopsis gene is expressed asymmetrically in floral meristems, even though they are destined to form symmetrical flowers. This suggests that, although the flowers of the common ancestor were probably radially symmetrical, they may have had an incipient asymmetry, evident at the level of early gene activity, which could have been recruited many times during evolution to generate asymmetric flowers.

Arabidopsis↗
PubMed2001

Goethe and the ABC model of flower development.

About 10 years ago, the ABC model for the genetic control of flower development was proposed. This model was initially based on the analysis of mutant flowers but has subsequently been confirmed by molecular analysis. This paper describes the 200-year history behind this model, from the late 18th century when Goethe arrived at his idea of plant metamorphosis, to the genetic studies on flower mutants carried out on Arabidopsis and Antirrhinum in the late 20th century.

Botany↗
PubMed2001

The gene fimbriata interacts non-cell autonomously with floral regulatory genes.

In Antirrhinum majus, one proposed role of the gene fimbriata (fim) is as a mediator between the floral meristem identify gene floricaula (flo) and floral organ identity genes such as deficiens (def) and plena (ple). The mechanism of fim activity is probably unique as, while the other genes in the hierarchy are thought to be transcription factors, fim is thought to target proteins to a ubiquitin-mediated destruction pathway. Both flo and def have been shown to act non-cell autonomously. We tested the hypotheses that (i) fim acts in a non-cell autonomous manner; and (ii) non-cell autonomy of flo might be through activation and subsequent non-cell autonomous activity of fim. Plants bearing an unstable fim allele were monitored for revertant shoots. Analysis of fim RNA expression in plants derived from revertant shoots, and segregation of revertant phenotype in progeny from revertant plants, indicated that all were periclinal chimeras with wild-type fim expression only in subepidermal layers. Despite the absence of fim in the epidermal layer, expression of downstream genes was normal, suggesting non-cell autonomous activity of fim. Subsequently, we tested the hypothesis that fim is the mediator of flo non-cell autonomy by examining fim expression in flo periclinal chimeras. In these chimeras, fim is activated in cells where flo is not expressed, indicating that fim cannot be the sole mediator of flo non-cell autonomy.

Chimera↗
PubMed2000

The expression of D-cyclin genes defines distinct developmental zones in snapdragon apical meristems and is locally regulated by the Cycloidea gene.

Three D-cyclin genes are expressed in the apical meristems of snapdragon (Antirrhinum majus). The cyclin D1 and D3b genes are expressed throughout meristems, whereas cyclin D3a is restricted to the peripheral region of the meristem, especially the organ primordia. During floral development, cyclin D3b expression is: (a) locally modulated in the cells immediately surrounding the base of organ primordia, defining a zone between lateral organs that may act as a developmental boundary; (b) locally modulated in the ventral petals during petal folding; and (c) is specifically repressed in the dorsal stamen by the cycloidea gene. Expression of both cyclin D3 genes is reduced prior to the cessation of cell cycle activity, as judged by histone H4 expression. Expression of all three D-cyclin genes is modulated by factors that regulate plant growth, particularly sucrose and cytokinin. These observations may provide a molecular basis for understanding the local regulation of cell proliferation during plant growth and development.

Amino Acid Sequence↗
PubMed1999

Control of organ asymmetry in flowers of Antirrhinum.

Organ asymmetry is thought to have evolved many times independently in plants. In Antirrhinum, asymmetry of the flower and its component organs requires cyc and dich gene activity. We show that, like cyc, the dich gene encodes a product belonging to the TCP family of DNA-binding proteins that is first expressed in the dorsal domain of early floral meristems. However, whereas cyc continues to be expressed throughout dorsal regions, expression of dich eventually becomes restricted to the most dorsal half of each dorsal petal. This correlates with the effects of dich mutations and ectopic cyc expression on petal shape, providing an indication that plant organ asymmetry can reflect subdomains of gene activity. Taken together, the results indicate that plant organ asymmetry can arise through a series of steps during which early asymmetry in the developing meristem is progressively built upon.

Amino Acid Sequence↗
PubMed1999

An epigenetic mutation responsible for natural variation in floral symmetry.

Although there have been many molecular studies of morphological mutants generated in the laboratory, it is unclear how these are related to mutants in natural populations, where the constraints of natural selection and breeding structure are quite different. Here we characterize a naturally occurring mutant of Linaria vulgaris, originally described more than 250 years ago by Linnaeus, in which the fundamental symmetry of the flower is changed from bilateral to radial. We show that the mutant carries a defect in Lcyc, a homologue of the cycloidea gene which controls dorsoventral asymmetry in Antirrhinum. The Lcyc gene is extensively methylated and transcriptionally silent in the mutant. This modification is heritable and co-segregates with the mutant phenotype. Occasionally the mutant reverts phenotypically during somatic development, correlating with demethylation of Lcyc and restoration of gene expression. It is surprising that the first natural morphological mutant to be characterized should trace to methylation, given the rarity of this mutational mechanism in the laboratory. This indicates that epigenetic mutations may play a more significant role in evolution than has hitherto been suspected.

Amino Acid Sequence↗
PubMed1999

The processing of secretogranin II in the peripheral nervous system: release of secretoneurin from porcine sympathetic nerve terminals.

The distribution of secretoneurin (SN), a peptide derived from secretogranin II (SgII), in the coeliac ganglion, the splenic nerve and the spleen was examined by immunohistochemistry. In the ganglion, SN immunoreactivity (IR) was unevenly distributed. Positive nerve terminals densely surrounded some postganglionic perikarya in which also intense SN-IR was present. In the crushed splenic nerves, intense immunoreactivities appeared proximal (but to a less extent also distal) to the crush of the nerve. Analysis by cytofluorimetric scanning (CFS) demonstrated that SN-IR and neuropeptide Y immunoreactivity (NPY-IR) were predominant in the axons proximal to the crush representing anterogradely transported components. Using radioimmunoassay (RIA) we demonstrated that upon electrical stimulation (10 Hz, 1 min) of the splenic nerve, significant amounts of SN-IR (64.2+/-2.3 fmol) were released together with NA (4. 1x106+/-0.2 fmol) and NPY (330.0+/-7.2 fmol) from the isolated perfused porcine spleen. To evaluate the processing of SgII in sympathetic neurons, boiled tissue extracts (coeliac ganglia and splenic nerve) and boiled spleen perfusate (used as a suitable source for vesicle derived peptides) were analysed by gel filtration chromatography followed by SN-RIA. In all cases immunoreactivity was present solely as SN, indicating that SgII was fully processed to the free peptide. The evidence that SN is transported to the nerve terminals and is released from the porcine spleen upon nerve stimulation, suggests that it may modulate adrenergic neurotransmission and may also play a role in the neuroimmune communication.

Animals↗
PubMed1999

The TCP domain: a motif found in proteins regulating plant growth and development.

The cycloidea (cyc) and teosinte branched 1 (tb1) genes code for structurally related proteins implicated in the evolution of key morphological traits. However, the biochemical function of CYC and TB1 proteins remains to be demonstrated. To address this problem, we have analysed the predicted secondary structure of regions conserved between CYC and TB1, and looked for related proteins of known function. One of the conserved regions is predicted to form a non-canonical basic-Helix-Loop-Helix (bHLP) structure. This domain is also found in two rice DNA-binding proteins, PCF1 and PCF2, where it has been shown to be involved in DNA-binding and dimerization. This indicates that the conserved domain most probably defines a new family of transcription factors, which we have termed the TCP family after its first characterised members (TB1, CYC and PCFs). Other plant proteins of unknown function also belong to this family. We have studied two of these in Arabidopsis and have shown that they are expressed in rapidly growing floral primordia. This, together with the proposed involvement of cyc and tb1 in influencing meristem growth, suggests that many members of the TCP family may affect cell division. Some of these genes may have been recruited during plant evolution to generate new morphological traits.

Amino Acid Sequence↗
PubMed1999

Can MRI replace a second look operation in cholesteatoma surgery?

The purpose of this paper is to investigate whether a magnetic resonance imaging (MRI) examination of the petrous bones could replace the conventional second look surgical procedure when a canal wall up tympanoplasty procedure has been performed during the first look surgery. Eighteen patients were examined with MRI prior to a second look surgical procedure. MRI was performed on a 1.5 T superconducting system. T2 weighted images before contrast and T1 weighted images after contrast (gadopentate dimeglumine) were obtained. Imaging results were compared with surgical findings. The poor radiosurgical correlation (50% and 61% after re-evaluation) suggests that, at the present time, MRI is not a valid alternative to a second look surgical intervention in the case of cholesteatoma treated by canal wall up tympanoplasty. In our study, MRI was not capable of differentiating small pearls of residual cholesteatoma from surrounding scar tissue.

Adolescent↗
PubMed1998

Central sleep apnea after interrupting longterm acetazolamide therapy.

One month administration of acetazolamide (ACET) (at sea level) improves periodic breathing and decreases the number of central apneas (CA) (De Backer et al., 1995 Am. J. Respir. Crit. Care Med. 151, 87-91) in nonhypercapnic central apnea syndrome. It remains unclear whether cessation of therapy would provoke recurrence of symptoms. In the present study we evaluated the number of CA after 1 and 6 months interruption of ACET therapy. Eight patients with central sleep apnea were included [central apnea index (CAI) > 5 or apnea and hypopnea index (AHI) > 10 and obstructive apnea index (OAI) < 5]. Polysomnography was repeated once after 1 month treatment (N2), after 1 month off treatment (N3) and after 6 months off treatment. CAI (25 +/- 10 at N1) decreased during N2 (4 +/- 2) and N3 (5 +/- 3) and remained low after N4 (3 +/- 1). However an increase in the number of obstructive apneas and central hypopneas could be observed together with a shift from central apnea to hypopnea after N4. Maybe ACET induces a long lasting resetting of the CO2 threshold which is still present after interruption of the therapy.

Acetazolamide↗
PubMed1998

Transcription pattern of a FIM homologue in Impatiens during floral development and reversion.

Flowering and reversion in Impatiens are characterised by gradual transitions of organ identity and constitute a unique system for the molecular and physiological study of floral organogenesis. The authors have isolated an Impatiens homologue of the FIM gene of Antirrhinum (UFO in Arabidopsis), Imp-FIM, and analysed its expression in three states of the terminal meristem: vegetative, floral, and reverted. In floral meristems, Imp-FIM transcription is associated with petal identity, as in Antirrhinum and Arabidopsis, but this is achieved through a novel transcription pattern, characterised by a high level of transcript within petal primordia. This novel transcription pattern could contribute to the more diffuse boundaries between organ types in Impatiens. In vegetative meristems, Imp-FIM is expressed in the axils of leaf primordia which are arranged in a spiral. A similar pattern is observed in reverted meristems in which leaf primordia are initiated in a whorled arrangement. This result indicates that the maintenance of floral phyllotaxis is not associated with a specific pattern of Imp-FIM transcription. Transcription of Imp-FIM in a non-reverting line is no different from that in the reverting line. Therefore, the lack of floral commitment in the reverting line does not seem to be responsible for Imp-FIM transcription within petals. The novel transcription pattern in petals, together with features of Impatiens that are reminiscent of fim and ufo mutant phenotypes suggest an evolutionary divergence for Imp-FIM regulation in this species.

Amino Acid Sequence↗
PubMed1997

Inflorescence commitment and architecture in Arabidopsis.

Flowering plants exhibit one of two types of inflorescence architecture: indeterminate, in which the inflorescence grows indefinitely, or determinate, in which a terminal flower is produced. The indeterminate condition is thought to have evolved from the determinate many times, independently. In two mutants in distantly related species, terminal flower 1 in Arabidopsis and centroradialis in Antirrhinum, inflorescences that are normally indeterminate are converted to a determinate architecture. The Antirrhinum gene CENTRORADIALIS (CEN) and the Arabidopsis gene TERMINAL FLOWER 1 (TFL1) were shown to be homologous, which suggests that a common mechanism underlies indeterminacy in these plants. However, unlike CEN, TFL1 is also expressed during the vegetative phase, where it delays the commitment to inflorescence development and thus affects the timing of the formation of the inflorescence meristem as well as its identity.

Amino Acid Sequence↗
PubMed1997

The induction and maintenance of flowering in Impatiens.

The mechanisms that establish the floral meristem are now becoming clearer, but the way in which flowering is maintained is less well understood. Impatiens balsamina provides a unique opportunity to address this question because reversion to vegetative growth can be obtained in a predictable way by transferring plants from inductive to non-inductive conditions. Following increasing amounts of induction, reversion takes place at progressively later stages of flower development. Partial flower induction and defoliation experiments show that a floral signal is produced in the cotyledon in response to inductive conditions and that this signal progressively diminishes after transfer to non-inductive conditions, during reversion. Therefore reversion in Impatiens is most likely due to the failure of leaves to become permanent sources of inductive signal in addition to the lack of meristem commitment to flowering. Analysis of the expression of the Impatiens homologues of the meristem identity genes floricaula and squamosa indicates that a change in floricaula transcription is not associated with the establishment or maintenance of the floral meristem in this species. Squamosa transcription is associated with floral development and petal initiation, and is maintained in existing petal or petaloid primordia even after the meristem has reverted. However, it is not expressed in the reverted meristem, in which leaves are initiated in whorled phyllotaxis and without axillary meristems, both characteristics usually associated with the floral meristem. These observations show that squamosa expression is not needed for the maintenance of these floral characters. The requirement for the production of the floral signal in the leaf during the process of flower development may reflect an additional function separate to that of squamosa activation; alternatively the signal may be required to ensure continued transcriptional activation in the meristem.

Amino Acid Sequence↗
PubMed1996

Origin of floral asymmetry in Antirrhinum.

Dorsoventral asymmetry in flowers is thought to have evolved many times from a radially symmetrical ancestral condition. The first gene controlling floral asymmetry, cycloidea in Antirrhinum, has been isolated. The cycloidea gene is expressed at a very early stage in dorsal regions of floral meristems, where it affects growth rate and primordium initiation. Expression continues through to later stages in dorsal primordia to affect the asymmetry, size and cell types of petals and stamens.

Alleles↗
PubMed1996

Control of inflorescence architecture in Antirrhinum.

Flowering plants exhibit two types of inflorescence architecture: determinate and indeterminate. The centroradialis mutation causes the normally indeterminate inflorescence of Antirrhinum to terminate in a flower. We show that centroradialis is expressed in the inflorescence apex a few days after floral induction, and interacts with the floral-meristem-identity gene floricaula to regulate flower position and morphology. The protein CEN is similar to animal proteins that associate with lipids and GTP-binding proteins. We propose a model for how different inflorescence structures may arise through the action and evolution of centroradialis.

Amino Acid Sequence↗
PubMed1996

Pathways for inflorescence and floral induction in Antirrhinum.

The presentation of flowers on a modified stem, the inflorescence, requires the integration of several aspects of meristem behaviour. In Antirrhinum, the inflorescence can be distinguished by its flowers, hairy stem, modified leaves, short internodes and spiral phyllotaxy. We show, by a combination of physiological, genetical and morphological analysis, that the various aspects of the inflorescence are controlled by three pathways. The first pathway, depends on expression of the floricaula gene, and is rapidly and discretely induced by exposure to long daylength. Activation of this pathway occurs in very young axillary meristems, resulting in a floral identity. In addition, the length of subtending leaves and hairiness of the stem are partially modified. The second pathway affects leaf size, internode length, and stem hairiness, but does not confer floral meristem identity. This pathway is induced by long daylength, but not as rapidly or discretely as the floricaula-dependent pathway. The third pathway controls the switch in phyllotaxy from decussate to spiral and is activated independently of daylength. The coordination of these three programmes ensures that apical and axillary meristem behaviour is integrated.

Base Sequence↗
PubMed1995

Control of flower development and phyllotaxy by meristem identity genes in antirrhinum.

The flower meristem identity genes floricaula (flo) and squamosa (squa) promote a change in phyllotaxy from spiral to whorled in Antirrhinum. To determine how this might be achieved, we have performed a combination of morphological, genetic, and expression analyses. Comparison of the phenotypes and RNA expression patterns of single and double mutants with the wild type showed that flo and squa act together to promote flower development but that flo is epistatic to squa with respect to early effects on phyllotaxy. We propose that a common process underlies the phyllotaxy of wildtype, flo, and squa meristem development but that the relative timing of primordium initiation or growth is altered. This process depends on two separable events: setting aside zones for potential primordium initiation and partitioning these zones into discrete primordia. Failure of the second event can lead to the formation of continuous double spirals, which are occasionally seen in flo mutants.

Base Sequence↗