Gene regulatory networks controlled by FLOWERING LOCUS C that confer variation in seasonal flowering and life history

Responses to environmental cues synchronize reproduction of higher plants to the changing seasons. The genetic basis of these responses has been intensively studied in the Brassicaceae. The MADS-domain transcription factor FLOWERING LOCUS C (FLC) plays a central role in the regulatory network that controls flowering of Arabidopsis thaliana in response to seasonal cues. FLC blocks flowering until its transcription is stably repressed by extended exposure to low temperatures in autumn or winter and, therefore, FLC activity is assumed to limit flowering to spring. Recent reviews describe the complex epigenetic mechanisms responsible for FLC repression in cold. We focus on the gene regulatory networks controlled by FLC and how they influence floral transition. Genome-wide approaches determined the in vivo target genes of FLC and identified those whose transcription changes during vernalization or in flc mutants. We describe how studying FLC targets such as FLOWERING LOCUS T, SQUAMOSA PROMOTER BINDING PROTEIN-LIKE 15, and TARGET OF FLC AND SVP 1 can explain different flowering behaviours in response to vernalization and other environmental cues, and help define mechanisms by which FLC represses gene transcription. Elucidating the gene regulatory networks controlled by FLC provides access to the developmental and physiological mechanisms that regulate floral transition.

Clonal sector analysis and cell ablation confirm a function for DORNROESCHEN-LIKE in founder cells and the vasculature in Arabidopsis

Inducible lineage analysis and cell ablation via conditional toxin expression in cells expressing the DORNRÖSCHEN-LIKE transcription factor represent an effective and complementary adjunct to conventional methods of functional gene analysis. Classical methods of functional gene analysis via mutational and expression studies possess inherent limitations, and therefore, the function of a large proportion of transcription factors remains unknown. We have employed two complementary, indirect methods to obtain functional information for the AP2/ERF transcription factor DORNRÖSCHEN-LIKE (DRNL), which is dynamically expressed in flowers and marks lateral organ founder cells. An inducible, two-component Cre-Lox system was used to express beta-glucuronidase GUS in cells expressing DRNL, to perform a sector analysis that reveals lineages of cells that transiently expressed DRNL throughout plant development. In a complementary approach, an inducible system was used to ablate cells expressing DRNL using diphtheria toxin A chain, to visualise the phenotypic consequences. These complementary analyses demonstrate that DRNL functionally marks founder cells of leaves and floral organs. Clonal sectors also included the vasculature of the leaves and petals, implicating a previously unidentified role for DRNL in provasculature development, which was confirmed in cotyledons by closer analysis of drnl mutants. Our findings demonstrate that inducible gene-specific lineage analysis and cell ablation via conditional toxin expression represent an effective and informative adjunct to conventional methods of functional gene analysis.

Functional dissection of the DORNRÖSCHEN-LIKE enhancer 2 during embryonic and phyllotactic patterning

The Arabidopsis DORNRÖSCHEN-LIKE enhancer 2 comprises a high-occupancy target region in the IM periphery that integrates signals for the spiral phyllotactic pattern and cruciferous arrangement of sepals. Transcription of the DORNRÖSCHEN-LIKE (DRNL) gene marks lateral organ founder cells (LOFCs) in the peripheral zone of the inflorescence meristem (IM) and enhancer 2 (En2) in the DRNL promoter upstream region essentially contributes to this phyllotactic transcription pattern. Further analysis focused on the phylogenetically highly conserved 100-bp En2^core element, which was sufficient to promote the phyllotactic pattern, but was recalcitrant to further shortening. Here, we show that En2^core functions independent of orientation and create a series of mutations to study consequences on the transcription pattern. Their analysis shows that, first, in addition to in the inflorescence apex, En2^core acts in the embryo; second, cis-regulatory target sequences are distributed throughout the 100-bp element, although substantial differences exist in their function between embryo and IM. Third, putative core auxin response elements (AuxREs) spatially activate or restrict DRNL expression, and fourth, according to chromatin configuration data, En2^core enhancer activity in LOFCs correlates with an open chromatin structure at the DRNL transcription start. In combination, mutational and chromatin analyses imply that En2^core comprises a high-occupancy target (HOT) region for transcription factors, which implements phyllotactic information for the spiral LOFC pattern in the IM periphery and coordinates the cruciferous array of floral sepals. Our data disfavor a contribution of activating auxin response factors (ARFs) but do not exclude auxin as a morphogenetic signal.

Spatiotemporal control of axillary meristem formation by interacting transcriptional regulators

Branching is a common feature of plant development. In seed plants, axillary meristems (AMs) initiate in leaf axils to enable lateral shoot branching. AM initiation requires a high level of expression of the meristem marker SHOOT MERISTEMLESS (STM) in the leaf axil. Here, we show that modules of interacting transcriptional regulators control STM expression and AM initiation. Two redundant AP2-type transcription factors, DORNRÖSCHEN (DRN) and DORNRÖSCHEN-LIKE (DRNL), control AM initiation by regulating STM expression. DRN and DRNL directly upregulate STM expression in leaf axil meristematic cells, as does another transcription factor, REVOLUTA (REV). The activation of STM expression by DRN/DRNL depends on REV, and vice versa. DRN/DRNL and REV have overlapping expression patterns and protein interactions in the leaf axil, which are required for the upregulation of STM expression. Furthermore, LITTLE ZIPPER3, another REV-interacting protein, is expressed in the leaf axil and interferes with the DRN/DRNL-REV interaction to negatively modulate STM expression. Our results support a model in which interacting transcriptional regulators fine-tune the expression of STM to precisely regulate AM initiation. Thus, shoot branching recruits the same conserved protein complexes used in embryogenesis and leaf polarity patterning.

Summary: Shoot branching uses interacting transcriptional regulators to fine-tune the spatiotemporal expression of STM and, thus, to precisely regulate axillary meristem initiation.

Class VIIIb APETALA2 Ethylene Response Factors in Plant Development

The APETALA2 (AP2) transcription factor superfamily in many plant species is extremely large. In addition to well-documented roles in stress responses, some AP2 members in arabidopsis, such as those of subgroup VIIIb, which includes DORNRÖSCHEN, DORNRÖSCHEN-LIKE, PUCHI, and LEAFY PETIOLE, are also important developmental regulators throughout the plant life cycle. Information is accumulating from orthologs of these proteins in important crop species that they influence key agronomic traits, such as the release of bud-burst in woody perennials and floral meristem identity and branching in cereals, and thereby represent potential for agronomic improvement. Given the increasing recognition of their developmental significance, this review highlights the function of these proteins and addresses their phylogenetic and evolutionary relationships.

DORNRÖSCHEN, DORNRÖSCHEN-LIKE, and PUCHI redundantly control floral meristem identity and organ initiation in Arabidopsis

The biphasic floral transition in Arabidopsis thaliana involves many redundant intersecting regulatory networks. The related AP2 transcription factors DORNRÖSCHEN (DRN), DORNRÖSCHEN-LIKE (DRNL), and PUCHI individually execute well-characterized functions in diverse developmental contexts, including floral development. Here, we show that their combined loss of function leads to synergistic floral phenotypes, including reduced floral merosity in all whorls, which reflects redundant functions of all three genes in organ initiation rather than outgrowth. Additional loss of BLADE-ON-PETIOLE1 (BOP1) and BOP2 functions results in the complete conversion of floral meristems into secondary inflorescence shoots, demonstrating that all five genes define an essential regulatory network for establishing floral meristem identity, and we show that their functions converge to regulate LEAFY expression. Thus, despite their largely discrete spatiotemporal expression domains in the inflorescence meristem and early floral meristem, PUCHI, DRN, and DRNL interdependently contribute to cellular fate decisions. Auxin might represent one potential non-cell-autonomous mediator of their gene functions, because PUCHI, DRN, and DRNL all interact with auxin transport and biosynthesis pathways.

Stem Cell Fate versus Differentiation: the Missing Link

The shoot apical meristem provides a microenvironment that ensures stem cell fate and proliferation via homeostasis between WUSCHEL (WUS) activity and CLAVATA signalling. New data from maize and arabidopsis reveal that an evolutionarily conserved signal deriving from primordium cells links WUS transcription to the morphogenetic programme.

The AP2-type transcription factors DORNRÖSCHEN and DORNRÖSCHEN-LIKE promote G1/S transition

The paralogous genes DORNRÖSCHEN (DRN) and DORNRÖSCHEN-LIKE (DRNL) encode AP2-type transcription factors that are expressed and act cell-autonomously in the central stem-cell zone or lateral organ founder cells (LOFCs) in the peripheral zone of the Arabidopsis shoot meristem (SAM), but their molecular contribution is unknown. Here, we show using the Arabidopsis thaliana MERISTEM LAYER 1 promoter that DRN and DRNL share a common function in cell cycle progression and potentially provide local competence for G1-S transitions in the SAM. Analysis of double transgenic DRN::erGFP and DRNL::erCERULEAN promoter fusion lines suggests that the trajectory of this cellular competence starts with DRN activity in the central stem-cell zone and extends locally via DRNL activity into groups of founder cells at the IM or FM periphery. Our data support the scenario that after gene duplication, DRN and DRNL acquired different transcription domains within the shoot meristem, but retained protein function that affects cell cycle progression, either centrally in stem cells or peripherally in primordial founder cells, a finding that is of general relevance for meristem function.

Founder-cell-specific transcription of the DORNRÖSCHEN-LIKE promoter and integration of the auxin response

Transcription of the DORNRÖSCHEN (DRNL) promoter marks lateral-organ founder cells throughout Arabidopsis development, from cotyledons to flowers or floral organs. In the inflorescence apex, DRNL::GFP depicts incipient floral phyllotaxy, and organs in the four floral whorls are differentially prepatterned: the sepals unidirectionally along an abaxial-adaxial axis, the four petals and two lateral stamens in two putative morphogenetic fields, and the medial stamens subsequently in a ring-shaped domain, before two groups of carpel founder cells are specified. The dynamic DRNL transcription pattern is controlled by three enhancer elements, which redundantly and synergistically control qualitative or quantitative aspects of expression, and differentially integrate the auxin response in Arabidopsis inflorescence and floral meristems. The high sequence conservation of all three enhancer elements among the Brassicaceae is striking, which suggests that densely packed cis-regulatory elements are conserved to recruit multiple transcription factors, including auxin response factors, into higher-order enhanceosome complexes. The spatial organization of the enhancers is also conserved, by a microsynteny that extends beyond the Brassicaceae, which relates to enhancer sharing, as the distal element En1 bidirectionally serves DRNL and the upstream At1g24600 gene; the genes are transcribed in opposite directions and possibly comprise a conserved functional chromatin domain.

Ocular surface involvements in ectrodactyly-ectodermal dysplasia-cleft syndrome

PURPOSE

To present the ocular manifestation of 2 cases of ectrodactyly-ectodermal dysplasia-cleft syndrome, a multiple congenital anomaly syndrome caused by a single point mutation of the p63 gene that controls epidermal development and homeostasis and to present treatment options.

CASE REPORTS AND DISCUSSION

Patient 1 presented with mild signs and symptoms of dry eye and limbal stem cell deficiency with retention of 20/30 vision. Patient 2 presented with severe signs and symptoms of limbal stem cell deficiency with diffuse corneal scarring and counting fingers vision. This second patient's course was complicated by allergic conjunctivitis and advanced steroid-induced glaucoma. The cause of visual loss in ectrodactyly-ectodermal dysplasia-cleft syndrome appears to be multifactorial and likely includes inflammation of the ocular surface, tear film abnormalities, eyelid abnormalities, and limbal stem cell deficiency. Treatment modalities including lubrication, contact lenses, and limbal stem cell transplantation are reviewed.

CONCLUSIONS

The ophthalmic conditions seen in ectrodactyly-ectodermal dysplasia-cleft syndrome frequently lead to vision loss. Early correct diagnosis and appropriate therapy are paramount because p63 gene mutations have a critical role in maintaining the integrity of the ocular surface in the setting of limbal stem cell deficiency, especially if there are other ocular surface insults such as lid disease, meibomian gland dysfunction and toxicity from topical medications. Patients should be monitored at regular, frequent intervals; and particular attention should be taken to avoid adverse secondary effects of these conditions and medications.

Arabidopsis floral phytomer development: auxin response relative to biphasic modes of organ initiation

In the Arabidopsis inflorescence meristem (IM), auxin is considered a prepatterning signal for floral primordia, whereas a centripetal mode of positional information for floral organ identity is inherent to the ABCE model. However, spatio-temporal patterns of organ initiation in each whorl at the earliest initiation stages are largely unknown. Evidence suggests that initial flower development occurs along an abaxial/adaxial axis and conforms to phytomer theory. Use of the founder cell marker DORNRÖSCHEN-LIKE (DRNL) as a tool in leafy, puchi, and apetala 1 cauliflower mutant backgrounds suggests that bract founder cells are marked at the IM periphery. The DRNL transcription domain in the wild-type IM is spatially discrete from DR5 expression, suggesting that bract initiation is independent of canonical auxin response. When bracts develop in lfy and puchi mutant floral primordia the initiation of lateral sepals precedes the specification of medial sepals compared with wild type, showing an interplay between bract and abaxial sepal founder cell recruitment. In the perianthia (pan) mutant background, DRNL expression indicates that a radial outer whorl arrangement derives from splitting of sepal founder cell populations at abaxial and adaxial positions. This splitting of incipient sepal primordia is partially dependent on PRESSED FLOWER (PRS) activity and implies that sepal specification is independent of WUSCHEL and CLAVATA3 expression, as both marker genes only regain activity in stage-2 flowers, when patterning of inner floral organs switches to a centripetal mode. The transition from an initially abaxial/adaxial into a centripetal patterning programme, and its timing represent an adaptive trait that possibly contributes to variation in floral morphology, especially unidirectional organ initiation.

Live imaging of DORNRÖSCHEN and DORNRÖSCHEN-LIKE promoter activity reveals dynamic changes in cell identity at the microcallus surface of Arabidopsis embryonic suspensions

KEY MESSAGE : Transgenic DRN::erGFP and DRNL::erGFP reporters access the window from explanting Arabidopsis embryos to callus formation and provide evidence for the acquisition of shoot meristem cell fates at the microcalli surface. The DORNRÖSCHEN (DRN) and DORNRÖSCHEN-LIKE (DRNL) genes encode AP2-type transcription factors, which are activated shortly after fertilisation in the zygotic Arabidopsis embryo. We have monitored established transgenic DRN::erGFP and DRNL::erGFP reporter lines using live imaging, for expression in embryonic suspension cultures and our data show that transgenic fluorophore markers are suitable to resolve dynamic changes of cellular identity at the surface of microcalli and enable fluorescence-activated cell sorting. Although DRN::erGFP and DRNL::erGFP are both activated in surface cells, their promoter activity marks different cell identities based on real-time PCR experiments and whole transcriptome microarray data. These transcriptome analyses provide no evidence for the maintenance of embryogenic identity under callus-inducing high-auxin tissue culture conditions but are compatible with the acquisition of shoot meristem cell fates at the surface of suspension calli.

Floral meristem initiation and emergence in plants

Plant development and architecture is regulated by meristems that initiate lateral organs on their flanks. The gene regulatory networks that govern the transition of a vegetative shoot apical meristem into an inflorescence meristem (IM), together with those necessary to specify floral meristem (FM) identity have been elucidated in Arabidopsis thaliana and are highly complex and redundant. FMs are initiated in the axils of cryptic bracts and evidence suggests that FMs emerge and differentiate along an abaxial/adaxial axis, in contrast to existing models of centroradial positional information within FMs. Real-time imaging has revealed dynamic cell division and gene expression patterns associated with incipient primordia in the IM. This review, however, outlines how little is known concerning the identity of these primordia, the timing of FM specification and commitment in relation to the establishment of FM identity, and the interplay between bract and FM founder cell recruitment and development.

Founder cell specification

Lateral organs arise from individual or groups of cells either on the flanks of meristems or within defined cellular positional contexts. The first event in organogenesis is founder cell specification. Auxin is one necessary signal in different organ specification contexts, but it is difficult to distinguish between correlative and causal signals and evidence is emerging that other signals exist and that the interplay between these signals is important for organ initiation. This review analyses the progress in understanding which signals contribute to founder cell specification and outlines the emerging complexities in the perception of positional information that are context-dependent and reliant on the establishment and coordination of different types of competencies.

Nanosized dendritic polyguanidilyated translocators for enhanced solubility, permeability, and delivery of gatifloxacin

PURPOSE

Dendrimeric polyguanidilyated translocators (DPTs) are nanosized novel dendrimers that efficiently translocate molecules across biological barriers. The purpose of this study was to develop a DPT that could serve as an ophthalmic delivery vehicle for gatifloxacin and to evaluate its in vitro and in vivo delivery after topical application.

METHODS

The gatifloxacin (GFX) solubility-enhancing property of a six-guanidine group-containing dendrimer (g6 DPT) was investigated as a function of pH and dendrimer concentration. Mechanisms of drug interaction with the dendrimer were investigated by using isothermal titration calorimetry (ITC), Fourier-transformed infrared spectroscopy (FTIR), and nuclear magnetic resonance spectroscopy (NMR). Permeability of the dendrimer was assessed in human corneal epithelial cells (HCECs) and across isolated bovine sclera-choroid-RPE (SCRPE). In vitro efficacy of the dendrimer formulation was evaluated with a time-to-kill assay for methicillin resistant Staphylococcus aureus (MRSA). In vivo delivery of GFX in a dendrimer eye drop formulation was studied in New Zealand White rabbits after a single dose or multiple doses over 3 weeks. Drug levels in various ocular tissues were analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS).

RESULTS

An optimized DPT-GFX formulation (final pH 5.9, no preservative) increased GFX solubility by fourfold. The dendrimer formed isotonically stable, nanosized (346-nm) complexes with GFX via ionic bond, hydrogen bond, and hydrophobic interactions. The dendrimer gained rapid entry into the HCECs (within 5 minutes) and increased the transport of GFX by 40% across the SCRPE in 6 hours. DPT-GFX exhibited a three times faster killing rate for MRSA when compared with GFX alone. In vivo administration of DPT-GFX (1.2% wt/vol) resulted in ∼13-fold, and ∼2-fold higher areas under the curve (AUCs) for tissue concentrations in conjunctiva and cornea, respectively, when compared with GFX (0.3%) after a single dose. Further, a single dose of DPT-GFX sustained aqueous humor and vitreous humor drug levels during the 24-hour study, with a t(1/2) of 9 and 32 hours, respectively. After multiple doses, similar advantages were seen with DPT-GFX.

CONCLUSIONS

The DPT forms stable complexes with GFX and enhances its solubility, permeability, anti-MRSA activity, and in vivo delivery, potentially allowing a once-daily dose regimen.

Auxin as compère in plant hormone crosstalk

The architecture of many hormone perceptions and signalling pathways has been recently well established, together with an awareness that plant hormone responses are the product of networks of interactions involving multiple hormones. As growth is quantitative, so are hormone responses, which underlie a systems approach to development and response. Auxin is arguably one of the best characterised hormones in plant development, and despite many excellent reviews on auxin perception, polar transport, and signal transduction, too little attention has been given to auxin crosstalk. This review, therefore, gives a précis of recent developments in hormone crosstalk involving auxin. For decades, the literature has described the involvement of multiple hormones in particular processes, although the mechanistic bases underlying points of crosstalk have been harder to pinpoint. Crosstalk falls into different categories, such as direct, indirect, or co-regulation. One conclusion for auxin crosstalk is that crosstalk operates extensively via the metabolism of other hormones, however, microarray approaches are increasingly identifying co-regulated genes and nodes of crosstalk at shared signalling components. Auxin crosstalk is often local, and is spatially and temporally regulated to provide adaptive value to environmental conditions and fine-tuning of responses.

Local auxin production: a small contribution to a big field

Auxin is a plant growth regulator involved in diverse fundamental developmental responses. Much is now known about auxin transport, via influx and efflux carriers, and about auxin perception and its role in gene regulation. Many developmental processes are dependent on peaks of auxin concentration and, to date, attention has been directed at the role of polar auxin transport in generating and maintaining auxin gradients. However, surprisingly little attention has focussed on the role and significance of auxin biosynthesis, which should be expected to contribute to active auxin pools. Recent reports on the function of the YUCCA flavin monooxygenases and a tryptophan aminotransferase in Arabidopsis have caused us to look again at the importance of local biosynthesis in developmental processes. Many alternative and redundant pathways of auxin synthesis exist in many plants and it is emerging that they may function in response to environmental cues.

BIM1, a bHLH protein involved in brassinosteroid signalling, controls Arabidopsis embryonic patterning via interaction with DORNROSCHEN and DORNROSCHEN-LIKE

The BIM1 protein which has been implicated in brassinosteroid (BR) signal transduction was identified from a two hybrid screen using the N-terminus, including the AP2 domain, of the transcription factors DORNROESCHEN (DRN) and DORNROESCHEN-LIKE (DRNL) which control embryonic patterning. The protein-protein interaction between BIM1 and DRN or DRNL was confirmed by co-immunoprecipitation and for DRN also in vivo by bimolecular fluorescence complementation. BIM1 can also physically interact with PHAVOLUTA (PHV), another interaction partner of DRN and DRNL. Loss of BIM1 function results in embryo patterning defects at low penetrance, including cell division defects in the hypophyseal region and apical domain defects such as cotyledon fusion and polycotyledony, in addition to polyembryony. BIM1 expression overlaps with that of DRN and DRNL from early globular embryo stages onwards. Higher order mutants between bim1, drn, drnl and phv suggest that although BIM1 may act partially redundantly with DRN in early embryo development, all genes function within the same pathway determining cotyledon development, supporting the hypothesis that they participate in a multimeric transcription factor complex. A role of BIM1 in embryonic development not only implicates a function for brassinosteroids in this process, but the interaction of BIM1 with DRN, involved with auxin signalling, represents a possible point of hormonal crosstalk in embryonic patterning and the first example of an interaction of components of the auxin and BR signalling pathways.

The role of DORNROESCHEN (DRN) and DRN-LIKE (DRNL) in Arabidopsis embryonic patterning

Appropriate embryonic patterning is amongst the most fundamental processes in plant development, necessary for the correct specification of root and shoot apical meristems which generate all post-germination organs of a plant. Many mutations have been characterized which disrupt embryonic pattern formation and many recent studies have focussed on the role of auxin in establishing apical-basal polarity. Our recent work has demonstrated the role of two redundant AP2 transcription factors, DORNROESCHEN (DRN) and DORNROESCHEN-LIKE (DRNL) in the control of embryo patterning, upstream of auxin perception and/or response and that DRN in turn, is regulated by auxin. We also suggest both genes are involved in the change from radial to bilateral symmetry in the globular embryo and are responsible for positional information of meristem-specific genes such as STM. The promiscuous interaction of DRN and DRNL proteins with the redundant family of class III HD-ZIP partners may represent a way by which embryonic cell specification can be controlled by combinations of transcription factor complexes, together with auxin.

Cotyledon organogenesis

The cotyledon represents one of the bases of classification within the plant kingdom, providing the name-giving difference between dicotyledonous and monocotyledonous plants. It is also a fundamental organ and there have been many reports of cotyledon mutants in many species. The use of these mutants where they have arisen in Arabidopsis has allowed us to unravel some of the complexities of embryonic patterning and cotyledon development with a high degree of resolution. The cloning of genes involved in cotyledon development from other species, together with physiological work, has supported the hypothesis that there exists a small number of orthologous gene hierarchies, particularly those involving auxin. The time is therefore appropriate for a summary of the regulation of cotyledon development gleaned from cotyledon mutants and regulatory pathways in the model species Arabidopsis and what can be inferred from cotyledon mutants in other species. There is an enormous variation in cotyledon form and development throughout the plant kingdom and this review focuses on debates about the phylogenetic relationship between mono- and dicotyledony, discusses gymnosperm cotyledon development and pleiocotyly in natural populations, and explores the limits of homology between cotyledons and leaves.

The AP2 transcription factors DORNROSCHEN and DORNROSCHEN-LIKE redundantly control Arabidopsis embryo patterning via interaction with PHAVOLUTA

DORNROSCHEN (DRN) (also known as ENHANCER OF SHOOT REGENERATION1; ESR1) and DRN-LIKE (DRNL; also known as ESR2) are two linked paralogues encoding AP2 domain-containing proteins. drn mutants show embryo cell patterning defects and, similarly to drnl mutants, disrupt cotyledon development at incomplete penetrance. drn drnl double mutants with weak or strong drnl alleles show more highly penetrant and extreme phenotypes, including a pin-like embryo without cotyledons, confirming a high degree of functional redundancy for the two genes in embryo patterning. Altered expression of PIN1::PIN1-GFP and DR5::GFP in drn mutant embryos places DRN upstream of auxin transport and response. A yeast two-hybrid screen with DRN followed by co-immunoprecipitation and bimolecular fluorescence complementation revealed PHAVOLUTA (PHV) to be a protein interaction partner in planta. drn phv double mutants show an increased penetrance of embryo cell division defects. DRNL can also interact with PHV and both DRN and DRNL can heterodimerise with additional members of the class III HD-ZIP family, PHABULOSA, REVOLUTA, CORONA and ATHB8. Interactions involve the PAS-like C-terminal regions of these proteins and the DRN/DRNL AP2 domain.

The AP2 transcription factors DORNROSCHEN and DORNROSCHEN-LIKE redundantly control Arabidopsis embryo patterning via interaction with PHAVOLUTA

DORNROSCHEN (DRN) (also known as ENHANCER OF SHOOT REGENERATION1; ESR1) and DRN-LIKE (DRNL; also known as ESR2) are two linked paralogues encoding AP2 domain-containing proteins. drn mutants show embryo cell patterning defects and, similarly to drnl mutants, disrupt cotyledon development at incomplete penetrance. drn drnl double mutants with weak or strong drnl alleles show more highly penetrant and extreme phenotypes, including a pin-like embryo without cotyledons, confirming a high degree of functional redundancy for the two genes in embryo patterning. Altered expression of PIN1::PIN1-GFP and DR5::GFP in drn mutant embryos places DRN upstream of auxin transport and response. A yeast two-hybrid screen with DRN followed by co-immunoprecipitation and bimolecular fluorescence complementation revealed PHAVOLUTA (PHV) to be a protein interaction partner in planta. drn phv double mutants show an increased penetrance of embryo cell division defects. DRNL can also interact with PHV and both DRN and DRNL can heterodimerise with additional members of the class III HD-ZIP family, PHABULOSA, REVOLUTA, CORONA and ATHB8. Interactions involve the PAS-like C-terminal regions of these proteins and the DRN/DRNL AP2 domain.

An alpha-crystallin gene, ACD31.2 from Arabidopsis is negatively regulated by FPF1 overexpression, floral induction, gibberellins, and long days

A gene sequence was isolated from a differential display experiment to find transcripts altered in expression by overexpression of FLORAL PROMOTING FACTOR 1 (FPF1) in Arabidopsis thaliana. The gene, ACD31.2, encodes an alpha-crystallin domain containing protein with homology to small heat shock proteins. In addition to down-regulation by FPF1 overexpression, the ACD31.2 transcript is also down-regulated by long days, floral induction, and by gibberellin in wild-type plants. Expression is highest in leaves and stems.

When negative is positive in functional genomics

The post-genomic era has caused classical approaches to analyse gene function to be reviewed and refined. Conventional reverse genetic approaches to predict gene function have drawbacks in terms of genetic redundancy and being limited mainly to well-characterized genomes. The relatively recent use of dominant-negative transgenes has been successful in elaborating certain pathways and it is now possible to extend this technique to convert transcription factors into dominant repressor functions by fusion to repressor domains such as ENGRAILED from Drosophila. This methodology opens up new possibilities to overcome genetic redundancy, to identify novel gene functions and also to apply information on conserved protein domains between species to repress heterologous protein function.

The effect of minoxidil on keratocyte proliferation in cell culture

PURPOSE

To determine if minoxidil inhibits keratocyte proliferation in a nontoxic manner.

METHODS

Rabbit keratocytes were cultured in Eagle's minimum essential medium supplemented with fetal bovine serum. Minoxidil varying in concentration from 10(0) to 10(3) micrograms/ml was added to the culture medium and incubated for 7 days. The cultures were inspected for morphologic appearance and the cell number was determined at 1, 3 and 7 days after the addition of minoxidil. After 7 days of incubation, minoxidil was withdrawn from the cell culture medium and the cells were examined 3 and 7 days thereafter. In addition, a nonradioactive cytotoxic assay was performed to determine if toxicity is associated with the presence of minoxidil.

RESULTS

Minoxidil inhibited keratocyte proliferation in a dose-dependent fashion. 29% of control growth was achieved when keratocytes were cultured for 7 days in 10(3) micrograms/ml, whereas 82% control growth was achieved when keratocytes were cultured in 10(2) micrograms/ml of minoxidil. Intermediate concentrations between 10(2) and 10(3) micrograms/ml produced a linear decline in cell counts in a dose-dependent fashion. The concentration of minoxidil required for 50% control growth at 7 days extrapolated from the dose-response curve was 600 micrograms/ml. Upon withdrawal of minoxidil, cell counts returned to baseline for concentrations of 10(2) micrograms/ml or less. Phase contrast microscopy revealed that the presence of minoxidil was associated with intercellular separation, enlargement of cell bodies and elongated processes. After the withdrawal of minoxidil, the cells in all media reassumed the morphological features of normal keratocytes which included a regular fusiform shape and extensive intercellular contact. The nonradioactive cytotoxic assay revealed the lack of cytotoxicity at all concentrations of minoxidil based on a lack of lactate dehydrogenase release.

CONCLUSIONS

Minoxidil inhibits keratocyte proliferation by a nontoxic mechanism. It might be particularly useful for modulating corneal wound healing following excimer laser photorefractive keratectomy.

Structure and function of the vp1 gene homologue from the resurrection plant Craterostigma plantagineum Hochst

A gene that is homologous to the vp1 genes from maize and rice, the Arabidopsis abi3 gene and PvAlf from Phaseolus vulgaris was isolated from the resurrection plant, Craterostigma plantagineum Hochst, The C. plantagineum gene (epvp1) encodes a protein of 688 amino acids and contains five introns at positions identical to those in the Arabidopsis, maize and rice homologues. The cpvp1 transcript is present in mature seeds and in young seedlings up to 8 days following germination. The ability of the cpvp1 gene product to activate target genes was demonstrated by transient expression experiments in tobacco protoplasts using reporter gene constructs containing the beta-glucuronidase (GUS) gene fused to the promoter of two late embryogenesis abundant (LEA)-like genes, CDeT27-45 and CDeT6-19 from C. plantagineum, or the promoter of a maize gene encoding a 22-kDa zein seed storage protein.

Analysis of cDNA clones encoding sucrose-phosphate synthase in relation to sugar interconversions associated with dehydration in the resurrection plant Craterostigma plantagineum Hochst

Sucrose-phosphate synthase (SPS) is a key enzyme in the regulation of sucrose metabolism, being responsible for the synthesis of sucrose 6-phosphate from fructose 6-phosphate and uridine 5'-diphosphate-glucose. We report on the isolation and characterization of cDNA clones encoding SPS from Craterostigma plantagineum Hochst., a resurrection plant in which the accumulation of sucrose is considered to play an important role in tolerance to severe protoplastic dehydration. Two distinct classes of cDNAs encoding SPS were isolated from C. plantagineum, and are represented by the clones Cpsps1 and Cpsps2. The transcripts corresponding to both cDNAs decrease to very low levels in dehydrating leaves of C. plantagineum. Only the Cpsps1 transcript occurs in the roots, where it is present at a higher level than in leaves and increases upon dehydration of the plant. Higher enzymatic activities have been determined in protein extracts of dehydrated tissues compared with untreated tissues, which correlates with an increase in protein levels. It is suggested that the overall regulation of SPS is strongly influenced by the changing composition of the cytoplasm in C. plantagineum leaves during the dehydration-rehydration cycle.

Polyhexamethylene biguanide (PHMB) in the treatment of experimental Fusarium keratomycosis

PURPOSE

We wanted to determine whether topical polyhexamethylene biguanide (PHMB) 0.02% was effective in the treatment of experimental Fusarium keratomycosis in rabbits.

METHODS

Fusarium solani keratomycosis was induced in the eyes of 12 New Zealand white rabbits. The rabbits were treated with PHMB 0.02% in one eye and placebo in the other eye for 6 days. The rabbits were evaluated in a masked fashion using a standardized system for clinical progression of the disease. Then the corneas were trephined and growth of F. solani in colony-forming units per milliliter (CFU/ml) determined.

RESULTS

Clinical evaluation demonstrated no significant mean difference (p > 0.10) in clinical scores between treated and control eyes on day 6 (0.583 +/- 2.503). There was a significant mean CFU difference (p = 0.06) between treated eyes and control eyes (182.5 +/- 314.44). Seven of 12 eyes (58%) in the PHMB group exhibited no growth, whereas two of 12 (17%) eyes reported no growth in the control group. One of 12 eyes (8%) reported > 100 CFU in the PHMB group, whereas seven of 12 eyes (58%) reported > 100 CFU in the control group.

CONCLUSIONS

PHMB 0.02% was effective in significantly reducing the fungal growth in our rabbit model of Fusarium keratomycosis. The future role of PHMB in the treatment of Fusarium keratitis needs to be further evaluated.

Ketorolac, prednisolone, and dexamethasone for postoperative inflammation

This 6-week, partially masked, three-arm, multicenter study was conducted to evaluate the postoperative anti-inflammatory efficacy of ketorolac, a cyclooxygenase inhibitor. The study setting was the clinical practice of six ophthalmic surgeons. The study enrolled 157 candidates for routine extracapsular cataract extraction or phaco-emulsification and posterior-chamber intraocular lens implantation. Patients who received any glucocorticoid or cyclooxygenase inhibitor within 1 week of surgery were excluded. All patients were treated with solutions of 0.5% ketorolac, 1% prednisolone acetate, or 0.1% dexamethasone instilled into the operative eye three times daily from 1 day before surgery to 4 weeks after surgery. Efficacy variables included the signs of anterior-segment inflammation, primarily cells and flare in the anterior chamber, as observed by slit-lamp biomicroscopy; fluorescein leakage across the blood-aqueous barrier as measured by fluorophotometry; and the rating of efficacy by the investigator. No significant differences were seen between ketorolac and either glucocorticoid in cells and flare. No significant differences were found in other signs of inflammation, except conjunctival hyperemia and Descemet's folds at week 2. Ketorolac showed significantly greater efficacy than the glucocorticoids against blood-aqueous barrier breakdown at day 5 and week 2, as demonstrated by the difference in fluorescein concentration between the operated and nonoperated eyes. Investigators did not detect any significant difference in rating for overall effectiveness and acceptability. These findings support the use of ketorolac as an alternative to glucocorticoids for the treatment of postoperative inflammation.

Dynamic shifts in corneal topography after radial and transverse keratotomy

PURPOSE

The authors aimed to quantitate the dynamic patterns of change in corneal topography after multistaged radial and transverse keratotomy using digitized video-keratography.

METHODS

Single and paired radial and transverse keratotomies, with videokeratoscopy between each stage and at the end of the procedure, were performed on fresh animal cadaver eyes using an artificial orbit system.

RESULTS

All incisions led to central flattening. A single radial keratotomy caused flattening adjacent to the incision, and steepening 180 degrees away. A paired radial keratotomy caused increased flattening in the meridian of the incisions, and less flattening 90 degrees away. A single transverse incision caused steepening adjacent to the incision and diffuse flattening elsewhere. A paired transverse incision caused flattening near the optical center along the meridian bisecting the incisions and steepening 90 degrees away.

CONCLUSION

The authors have demonstrated that computerized videokeratography can be used successfully to systematically quantitate dioptric shifts in multiple hemimeridians and measurement zone diameters after refractive surgery.

Localization and characterization of binding sites for endothelin in Harder's gland in rabbits

The characterization and localization of binding sites for endothelin-1 (ET-1) labeled with iodine 125I were investigated in homogenized tissues and sections of Harder's glands of normal rabbits. The membrane of Harder's glands was harvested and incubated with 125I-ET-1 (0.25-1 nmol/L) in 20 +/- 4 mg of protein per 0.25 mL at 37 degrees C for 90 min in the presence of protease inhibitors. Specific labeling was assessed by coincubating unlabeled ET-1, ET-2, ET-3 and other unrelated cytokines. The tissue labeled with 125I-ET-1 was collected by filtration and counted in a gamma counter. For an in vitro autoradiography study, 15 microns cryostat sections were incubated with 125I-ET-1 (0.1 nmol/L). They were fixed, dipped in liquid emulsion and kept for 6 days before development. Membrane counting showed that the binding of 125I-ET-1 to Harder's gland was saturable. Scatchard data analysis revealed one class of binding with a dissociation constant (Kd) of 0.33 nmol/L and a maximal density of binding (Bmax) of 794 attomole/mg of protein. The binding was inhibited most by ET-1, followed by ET-2 and then ET-3 but not by unrelated peptides. Emulsion-dipped slides with sections showed specific high-density labeling mainly over structures identified from serial sections stained by hematoxylin-eosin as the walls of capillaries, arterioles, arteries, and veins of the glands. Less dense binding was found in both white and pink lobes of the gland. No binding was found in fat and connective tissues. The distribution of endothelin action sites in the glandular blood vessels and Harder's gland suggests that the peptide may have a role in the regulation of blood circulation and glandular secretion in the normal rabbit.

Photosynthesis and nutrient supply in needles of Sitka spruce [Picea sitchensis (Bong.) Carr.]

Growth and photosynthetic development were measured for currently developing needles of young trees of Sitka spruce [Picea sitchensis (Bong.) Carr.] throughout their fourth growth season. Treatments included trees that were fully fertilized (control), trees deficient in phosphorus (-P), or nitrogen (-N), and trees initially deficient but then supplied with phosphorus (-PR) or nitrogen (-NR). Growth was measured in terms of needle projected area, and the photosynthetic components measured were pigment concentration, net photosynthetic rate, (P_N ), activity of ribulose-1,5-bisphosphate carboxylase, (RuBPC), stomatal conductance to CO₂ , (G_s ), and the intercellular partial pressure of CO₂ , (C_i ). Needle growth was rapid, beginning in early May and being complete by the end of the month or early in June. Free growth occurred in the -NR treatment. Photosynthesis increased throughout the season, reaching a peak in August, with some variables subsequently showing a decrease in value. P_N increased more rapidly during needle expansion than either chlorophyll concentration or RuBPC activity. Phosphorus deficiency led to a reduction in RuBPC activity, which was restored to the control value following Refertilization with P. Nitrogen deficiency severely reduced values of all variables studied, except C_i , which was higher than for the controls. Refertilization of -N trees caused a very rapid increase in values of all variables, with an increase in C_i , representing a larger increase in mesophyll conductance to CO₂ , (G_M ), than G_S , P_N and RuBPC activity were significantly correlated with total chlorophyll concentration for all treatments, but P_N was not correlated with G_S or RuBPC activity.

Interferon-alpha and interferon-gamma induced modulation of proteins in human corneal fibroblasts

Little is known about the effects of interferon (IFN) on cell function in the eye. We have analyzed the effect of INF-alpha and IFN-gamma on the expression of proteins in cultured human corneal fibroblasts. Treatment with IFN-alpha increased the synthesis of proteins of 84, 76, 52, and 28 kD and decreased the synthesis of a 72-kD protein. Treatment with IFN-gamma increased the synthesis of proteins of 83, 66, 64, 54, and 47 kD. The effect of IFN-alpha and IFN-gamma were first detected at 5-9 h and 9 h, respectively, after the addition of the IFNs and were maximal at 17 and 24 h, respectively. Most of the changes were seen at doses of 1 x 10(1) to 1 x 10(2) U/ml of IFN-alpha or IFN-gamma and were maximal at 1 x 10(2) to 1 x 10(3) U/ml. Thus, each IFN induced distinct proteins based on apparent molecular weight and isoelectric point. These results show that IFN-alpha and IFN-gamma affect the synthesis of small groups of distinct proteins in human corneal fibroblasts.

Conjunctivitis of the newborn

Infectious conjunctivitis of the newborn is caused by a wide variety of microorganisms. The ocular findings may be part of a widespread systemic infection. Clinical presentations are not diagnostic of the cause, and a microbiologic work-up with cytology, cultures, and microbial sensitivities is mandatory. The selection of specific antimicrobial therapy is based on the findings of laboratory studies. Prophylaxis with silver nitrate solution, 1.0% tetracycline, or 0.05% erythromycin ointment is effective for the prevention of gonococcal and chlamydial conjunctivitis in the newborn.

Indications for penetrating keratoplasty: 1980-1988

A retrospective analysis was undertaken of the clinical diagnoses of 1594 eyes that underwent penetrating keratoplasty performed in a private-referral corneal practice over a 9-year period, 1980-1988. The seven most common indications for surgery were keratoconus (24.0%), pseudophakic or aphakic bullous keratopathy (21.2%), corneal scarring (13.9%), Fuchs' endothelial dystrophy (12.5%), regraft (8.1%), and herpetic keratitis (5.3%). Keratoconus was the leading indication from 1980 to 1985. From 1985 to 1988, pseudophakic bullous keratopathy became the leading indication and correlates well with known complications associated with closed-loop anterior chamber lenses, which were widely used during the early 1980s. Less frequent indications for penetrating keratoplasty included the following: infectious (nonviral) keratitis (3.5%); acute or chronic ulcerative keratitis (2.7%); interstitial keratitis (1.8%); mechanical trauma (1.5%); other (non-Fuchs') corneal dystrophies (1.4%); congenital opacities (0.8%); and chemical burns (0.5%).

In vivo induction of Ia expression in murine cornea after intravitreal injection of interferon-gamma

Intravitreal injection of interferon gamma (IFN-gamma) induces increased expression of Class II major histocompatibility complex (Ia) antigen expression on corneal endothelial cells and stromal fibroblasts. In contrast, IFN-gamma has no detectable effect on Ia antigen expression in epithelium. Induction of Ia antigen expression was rapid with increases detectable as early as 6-12 hours after a single injection of 1 x 10(5) units. Expression peaked at 24-48 hours and decreased to background levels by 120 hours. The Ia antigen expression increased in a dose-dependent manner, and IFN-gamma treatment also induced the synthesis of increased amounts of a 65-kilodalton (kD) protein in the cornea. Increased levels of this 65-kd protein are seen as early as 12 hours after treatment and can be induced with as little as 1 x 10(2) units of IFN-gamma. The function of the 65-kd protein is unknown. This model should be useful in studies on in vivo modulation of Ia antigen expression.

Heparin and infarct coronary artery patency after streptokinase in acute myocardial infarction

Anticoagulant therapy is frequently used after thrombolytic agents in the treatment of acute myocardial infarction (AMI) although it is unclear that such therapy will prevent subsequent infarct vessel reocclusion. The role of duration of heparin therapy in maintaining infarct artery patency was studied retrospectively in 53 consecutive AMI patients who received streptokinase therapy and underwent coronary angiography acutely and at 14 +/- 1 days. Of the 39 patients with initial infarct vessel patency, patency at follow-up angiography was observed in 100% (22 of 22) of those who received greater than or equal to 4 days of intravenous heparin but in only 59% (10 of 17) of those patients who received less than 4 days of heparin (p less than 0.05). Of the 14 patients not initially recanalized after streptokinase, patent infarct-related arteries at follow-up angiography were found in 3 of 8 (38%) treated with greater than or equal to 4 days of heparin therapy but in none of the 6 patients treated for less than 4 days (difference not significant). No significant difference in hemorrhagic complications was noted between the short- and long-term heparin treatment groups. Thus, greater than or equal to 4 days of intravenous heparin therapy after successful streptokinase therapy in AMI is more effective in maintaining short-term infarct vessel patency than a shorter duration of therapy and it may maintain the short-term patency of the infarct vessel in those patients who later spontaneously recanalize.

Needle growth in Sitka spruce (Picea sitchensis): effects of nutrient deficiency and needle position within shoots

Needle development and shoot growth were studied in 14- and 20-year-old Sitka spruce (Picea sitchensis (Bong.) Carr.) planted on an oligotrophic peat and fertilized with N, P and K (control), N and P (-K), N and K (-P) or unfertilized (-NPK). Shoot extension, needle number, and the size and number of needle cells were observed throughout the season. Beginning with bud burst in early May, needle growth continued for nine weeks in the control treatment. Needle growth in the mineral deficiency treatments terminated at the same time as in the controls, although it did not begin until up to three weeks later than in the control trees. Needles developed acropetally along the shoot, with basal needles completing their development first. Cell division in needles of control trees lasted about 3 weeks, with cell expansion continuing for a further 3 weeks. Initial mean cell cycle times were shortest for proximal needles following bud burst, but lengthened as the season progressed. Cell number increased from 6600 in the primordia to 200 000 in mature needles. Final needle dimensions and cell number varied according to the position of the needle on the shoot. The largest needles with the most cells were near the middle of the shoot. Relative to the controls, all mineral deficiency treatments reduced shoot length, bud and needle dimensions, and needle cell number, particularly the -P treatment. Potassium and P deficiency treatments reduced primordial cell number by up to 42%, whereas final mean cell size was 30% greater in the -P treatment, 17% greater in the -NPK treatment, but 14% smaller in the -K treatment. Mean cell size was constant for needles at all positions in any particular treatment at any time, so that final needle size was determined by cell number alone. Needle dry weight/fresh weight ratio continued to increase until early August, with significantly higher ratios in the -K and -P treatments than in the controls.

Lack of T6 induction on human corneal Langerhans cells in vitro

Previous studies have shown that Langerhans cells (LC) in normal human corneas differ from their counterparts in other epithelia (eg, skin, gingival, cervical) by their lack of the thymocyte antigen T6 on their membranes. In those studies only three out of four very young infant corneas (newborn, 3-day-, 8-day-old) have displayed positive T6 staining to date. Corneas from older infants and adults have demonstrated no such staining. This study tested the capacity of corneal LC to express T6 by in vitro induction with several immunomodulating agents. Human gamma interferon (IFN gamma was tested at 1000 U/ml, 500 U/ml and 100 U/ml. Interleukin-1 (IL-1) was tested at 100 U/ml, 50 U/ml and 20 U/ml. Thymopoietin pentapeptide (TP-5) was tested at 10 micrograms/ml, 1 micrograms/ml and 0.1 microgram/ml. Combinations of these agents were also tested in a similar fashion. None of these immunomodulating agents or combinations of them were able to induce T6 expression on normal corneal LC. This may reflect an innate incapacity of these cells to express this antigen or dosage requirements in excess of those tested.

Biocompatibility of hydrogen peroxide in soft contact lens disinfection: antimicrobial activity vs. biocompatibility--the balance

Critical factors of soft contact lens care include adequate disinfection and neutralization of the chemical constituents of the disinfecting system before reinsertion. Three cases of microbial keratitis are described that exemplify the critical nature of disinfection with adequate antimicrobial activity. Disinfection rates are described for a 3% solution of hydrogen peroxide (H2O2) against multiple microorganisms. The results indicate that H2O2 is equivalent to heat disinfection when used for appropriate lengths of time. Problems associated with chemical disinfection include lens fit alterations, which may lead to epithelial trauma. However, unless antimicrobial chemicals can be rinsed, neutralized, or degraded, they can also injure the corneal and conjunctival epithelium. Repeated exposure of the corneal epithelium to oxidizing agents renders it vulnerable to complications.

Therapeutic uses of contact lenses

Therapeutic use of contact lenses is an essential element in ophthalmic care. Materials currently in use include polymethyl methacrylate (PMMA), cellulose acetate butyrate, siloxane-containing polymethacrylates, silicones, and hydrogels. Suitability of a material for therapeutic contact lens use is determined by the physical, chemical, and mechanical properties (notably gas permeability and hydrophilicity, but also lipid absorption and lens movement, among others) and the condition to be treated; fabrication techniques are likewise important, affecting lens diameter and base curve. Selection and fitting of therapeutic contact lenses requires knowledge of how different contact lenses affect corneal physiology, as well as an understanding of the mechanisms whereby a contact lens can be therapeutic. In addition to these topics, general fitting guidelines are discussed, and results of therapeutic lens use in selected clinical situations (including recurrent erosion, metaherpetic ulcers and other epithelial defects, and keratitis sicca, and other dry eye states). Common therapeutic contact lens complications and their treatment are also discussed.