The stomatal fates: Understanding initiation and enforcement of stomatal cell fate transitions.

In the stomatal lineage, repeated arcs of initiation, stem-cell proliferation, and terminal cell fate commitment are displayed on the surface of aerial organs. Over the past two decades, the core transcription and signaling elements that guide cell divisions, patterning, and fate transitions were defined. Here we highlight recent work that extends the core using a variety of cutting-edge techniques in different plant species. New work has discovered transcriptional circuits that initiate and reinforce stomatal fate transitions, while also enabling the lineage to interpret and respond to environmental inputs. Recent developments show that some key stomatal factors are more flexible or potentially even interchangeable, opening up avenues to explore stomatal fates and regulatory networks.

A cell size threshold triggers commitment to stomatal fate in Arabidopsis.

How flexible developmental programs integrate information from internal and external factors to modulate stem cell behavior is a fundamental question in developmental biology. Cells of the Arabidopsis stomatal lineage modify the balance of stem cell proliferation and differentiation to adjust the size and cell type composition of mature leaves. Here, we report that meristemoids, one type of stomatal lineage stem cell, trigger the transition from asymmetric self-renewing divisions to commitment and terminal differentiation by crossing a critical cell size threshold. Through computational simulation, we demonstrate that this cell size-mediated transition allows robust, yet flexible termination of stem cell proliferation, and we observe adjustments in the number of divisions before the differentiation threshold under several genetic manipulations. We experimentally evaluate several mechanisms for cell size sensing, and our data suggest that this stomatal lineage transition is dependent on a nuclear factor that is sensitive to DNA content.

Extensive embryonic patterning without cellular differentiation primes the plant epidermis for efficient post-embryonic stomatal activities.

Plant leaves feature epidermal stomata that are organized in stereotyped patterns. How does the pattern originate? We provide transcriptomic, imaging, and genetic evidence that Arabidopsis embryos engage known stomatal fate and patterning factors to create regularly spaced stomatal precursor cells. Analysis of embryos from 36 plant species indicates that this trait is widespread among angiosperms. Embryonic stomatal patterning in Arabidopsis is established in three stages: first, broad SPEECHLESS (SPCH) expression; second, coalescence of SPCH and its targets into discrete domains; and third, one round of asymmetric division to create stomatal precursors. Lineage progression is then halted until after germination. We show that the embryonic stomatal pattern enables fast stomatal differentiation and photosynthetic activity upon germination, but it also guides the formation of additional stomata as the leaf expands. In addition, key stomatal regulators are prevented from driving the fate transitions they can induce after germination, identifying stage-specific layers of regulation that control lineage progression during embryogenesis.

De novo stem cell establishment in meristems requires repression of organ boundary cell fate.

Stem cells play important roles in animal and plant biology, as they sustain morphogenesis and tissue replenishment following aging or injury. In plants, stem cells are embedded in multicellular structures called meristems. The formation of new meristems is essential for the plastic expansion of the highly branched shoot and root systems. In particular, axillary meristems (AMs) that produce lateral shoots arise from the division of boundary domain cells at the leaf base. The CUP-SHAPED COTYLEDON (CUC) genes are major determinants of the boundary domain and are required for AM initiation. However, how AMs get structured and how stem cells become established de novo remain elusive. Here, we show that two NGATHA-LIKE (NGAL) transcription factors, DEVELOPMENT-RELATED PcG TARGET IN THE APEX4 (DPA4)/NGAL3 and SUPPRESSOR OF DA1-1 7 (SOD7)/NGAL2, redundantly repress CUC expression in initiating AMs of Arabidopsis thaliana. Ectopic boundary fate leads to abnormal growth and organization of the AM and prevents de novo stem cell establishment. Floral meristems of the dpa4 sod7 double mutant show a similar delay in de novo stem cell establishment. Altogether, while boundary fate is required for the initiation of AMs, our work reveals how it is later repressed to allow proper meristem establishment and de novo stem cell niche formation.

A network of transcriptional repressors modulates auxin responses.

The regulation of signalling capacity, combined with the spatiotemporal distribution of developmental signals themselves, is pivotal in setting developmental responses in both plants and animals1. The hormone auxin is a key signal for plant growth and development that acts through the AUXIN RESPONSE FACTOR (ARF) transcription factors2-4. A subset of these, the conserved class A ARFs5, are transcriptional activators of auxin-responsive target genes that are essential for regulating auxin signalling throughout the plant lifecycle2,3. Although class A ARFs have tissue-specific expression patterns, how their expression is regulated is unknown. Here we show, by investigating chromatin modifications and accessibility, that loci encoding these proteins are constitutively open for transcription. Through yeast one-hybrid screening, we identify the transcriptional regulators of the genes encoding class A ARFs from Arabidopsis thaliana and demonstrate that each gene is controlled by specific sets of transcriptional regulators. Transient transformation assays and expression analyses in mutants reveal that, in planta, the majority of these regulators repress the transcription of genes encoding class A ARFs. These observations support a scenario in which the default configuration of open chromatin enables a network of transcriptional repressors to regulate expression levels of class A ARF proteins and modulate auxin signalling output throughout development.

Specification and regulation of vascular tissue identity in the Arabidopsis embryo.

Development of plant vascular tissues involves tissue identity specification, growth, pattern formation and cell-type differentiation. Although later developmental steps are understood in some detail, it is still largely unknown how the tissue is initially specified. We used the early Arabidopsis embryo as a simple model to study this process. Using a large collection of marker genes, we found that vascular identity was specified in the 16-cell embryo. After a transient precursor state, however, there was no persistent uniform tissue identity. Auxin is intimately connected to vascular tissue development. We found that, although an AUXIN RESPONSE FACTOR5/MONOPTEROS (ARF5/MP)-dependent auxin response was required, it was not sufficient for tissue specification. We therefore used a large-scale enhanced yeast one-hybrid assay to identify potential regulators of vascular identity. Network and functional analysis of candidate regulators suggest that vascular identity is under robust, complex control. We found that one candidate regulator, the G-class bZIP transcription factor GBF2, can modulate vascular gene expression by tuning MP output through direct interaction. Our work uncovers components of a gene regulatory network that controls the initial specification of vascular tissue identity.

A PXY-Mediated Transcriptional Network Integrates Signaling Mechanisms to Control Vascular Development in Arabidopsis.

The cambium and procambium generate the majority of biomass in vascular plants. These meristems constitute a bifacial stem cell population from which xylem and phloem are specified on opposing sides by positional signals. The PHLOEM INTERCALATED WITH XYLEM (PXY) receptor kinase promotes vascular cell division and organization. However, how these functions are specified and integrated is unknown. Here, we mapped a putative PXY-mediated transcriptional regulatory network comprising 690 transcription factor-promoter interactions in Arabidopsis (Arabidopsis thaliana). Among these interactions was a feedforward loop containing transcription factors WUSCHEL HOMEOBOX RELATED14 (WOX14) and TARGET OF MONOPTEROS6 (TMO6), each of which regulates the expression of the gene encoding a third transcription factor, LATERAL ORGAN BOUNDARIES DOMAIN4 (LBD4). PXY signaling in turn regulates the WOX14, TMO6, and LBD4 feedforward loop to control vascular proliferation. Genetic interaction between LBD4 and PXY suggests that LBD4 marks the phloem-procambium boundary, thus defining the shape of the vascular bundle. These data collectively support a mechanism that influences the recruitment of cells into the phloem lineage, and they define the role of PXY signaling in this context in determining the arrangement of vascular tissue.

[Psychiatric symptoms in a child with gluten sensitivity]. / Psychische klachten bij kind met glutensensitiviteit.

BACKGROUND: Non-celiac gluten sensitivity (NCGS) is a diagnosis that is increasingly being reported. Psychiatric symptoms can be a rare but serious manifestation of this new clinical entity. CASE REPORT: A 13-year-old girl consulted the paediatrician with abdominal pain, diarrhoea, bloating, and compulsive thoughts and fears; these disappeared on a gluten-free diet. Celiac disease and wheat allergy were excluded. Double-blind placebo-controlled gluten challenge confirmed the diagnosis NCGS. CONCLUSION: Consider a diagnosis of NCGS in patients with psychiatric symptoms in combination with abdominal symptoms.

Serious complications after button battery ingestion in children.

Serious and fatal complications after button battery ingestion are increasing worldwide. The aim of this study is to describe serious complications after battery ingestion in children in the Netherlands.All pediatric gastroenterologists in the Netherlands performing upper endoscopies were asked to report all serious complications after battery ingestion in children (0-18 years) between 2008 and 2016 retrospectively.Sixteen serious complications were reported: death after massive bleeding through esophageal-aortal fistula (n = 1), esophageal-tracheal fistula (n = 5), stenosis after (suspected) perforation and mediastinitis (n = 5), (suspected) perforation and mediastinitis (n = 3), vocal cord paralysis (n = 1), and required reintubation for dyspnea and stridor (n = 1). The median time interval between ingestion and presentation was 5 (IQR 2-258) h. All children were ≤ 5 (median 1.4; IQR 0.9-2.1) years. Vomiting (31.3%), swallowing/feeding problems (31.3%), and fever (31.3%) were the most common presenting symptoms; however, 18.8% of the patients were asymptomatic (n = 1 missing). All batteries were button batteries (75% ≥ 20 mm; 18.8% < 20 mm; n = 1 missing). The batteries were removed by esophagogastroduodenoscopy (50%) and rigid endoscopy (37.5%) or surgically (12.5%). CONCLUSION: Sixteen serious complications occurred after small and large button batteries ingestion between 2008 and 2016 in both symptomatic and asymptomatic children in the Netherlands. Therefore, immediate intervention after (suspected) button battery ingestion is required. What is Known: • Button battery ingestion may result in serious and fatal complications. • Serious and fatal complications after button battery ingestion are increasing worldwide. What is New: • Sixteen serious complications after button battery ingestion occurred during 2008-2016 in children in the Netherlands. • Serious complications were also caused by small batteries (< 20 mm) in the Netherlands and also occurred in asymptomatic Dutch children.

E-Healthcare for Celiac Disease-A Multicenter Randomized Controlled Trial.

OBJECTIVE: To evaluate the (cost-)effectiveness of online consultations in follow-up of patients with celiac disease (CD). STUDY DESIGN: Multicenter randomized, controlled trial involving 304 patients aged ≤25 years with CD for ≥1 year, randomized to an online (n = 156) or outpatient consultation (n = 148). An online consultation included questionnaires for symptom and growth measurement. Antitransglutaminase-type-2 antibodies were determined using a point-of-care (POC) test. Controls had a traditional consultation with antitransglutaminase-type-2 antibodies testing in laboratories. Both groups completed questionnaires concerning CD-specific health-related quality of life (HRQOL), gluten-free diet adherence, and patient satisfaction. Six months later, participants repeated HRQOL and patient satisfaction questionnaires and the POC test. The primary outcome was anti-transglutaminase-type-2 antibodies after 6 months, and the secondary outcomes were health problems, dietary adherence, HRQOL, patient satisfaction, and costs. RESULTS: The performance of the POC test was inferior to laboratory testing (2/156 positive POC tests vs 13/148 positive laboratory tests; P = .003). Health problems were detected significantly more frequently using online consultation. The detection of growth problems and dietary transgressions was similar. HRQOL (from 1 [good] to 5 [poor]) improved after online consultation (from 3.25 to 3.16 [P = .013] vs controls from 3.10 to 3.23; P = .810). Patient satisfaction (from 1 [low] to 10 [high]) was 7.6 (online) vs 8.0 (controls; P = .001); 58% wished to continue online consultations. Mean costs per participant during the studied period were €202 less for the online group (P < .001). CONCLUSIONS: The primary outcome could not be tested because the POC test was unreliable. Nevertheless, our results indicate that online consultations for children and young adults with CD are cost saving, increase CD-specific HRQOL, and are satisfactory for the majority. TRIAL REGISTRATION: Trialregister.nl: NTR3688.

Auxin response cell-autonomously controls ground tissue initiation in the early Arabidopsis embryo.

Plant organs are typically organized into three main tissue layers. The middle ground tissue layer comprises the majority of the plant body and serves a wide range of functions, including photosynthesis, selective nutrient uptake and storage, and gravity sensing. Ground tissue patterning and maintenance in Arabidopsis are controlled by a well-established gene network revolving around the key regulator SHORT-ROOT (SHR). In contrast, it is completely unknown how ground tissue identity is first specified from totipotent precursor cells in the embryo. The plant signaling molecule auxin, acting through AUXIN RESPONSE FACTOR (ARF) transcription factors, is critical for embryo patterning. The auxin effector ARF5/MONOPTEROS (MP) acts both cell-autonomously and noncell-autonomously to control embryonic vascular tissue formation and root initiation, respectively. Here we show that auxin response and ARF activity cell-autonomously control the asymmetric division of the first ground tissue cells. By identifying embryonic target genes, we show that MP transcriptionally initiates the ground tissue lineage and acts upstream of the regulatory network that controls ground tissue patterning and maintenance. Strikingly, whereas the SHR network depends on MP, this MP function is, at least in part, SHR independent. Our study therefore identifies auxin response as a regulator of ground tissue specification in the embryonic root, and reveals that ground tissue initiation and maintenance use different regulators and mechanisms. Moreover, our data provide a framework for the simultaneous formation of multiple cell types by the same transcriptional regulator.

A brief history of the TDIF-PXY signalling module: balancing meristem identity and differentiation during vascular development.

474 I. 474 II. 475 III. 475 IV. 477 V. 477 VI. 477 VII. 479 VIII. 481 482 References 482 SUMMARY: A significant proportion of terrestrial biomass is constituted of xylem cells that make up woody plant tissue. Xylem is required for water transport, and is present in the vascular tissue with a second conductive tissue, phloem, required primarily for nutrient transport. Both xylem and phloem are derived from cell divisions in vascular meristems known as the cambium and procambium. One major component that influences several aspects of plant vascular development, including cell division in the vascular meristem, vascular organization and differentiation of vascular cell types, is a signalling module characterized by a peptide ligand called TRACHEARY ELEMENT DIFFERENTIATION INHIBITORY FACTOR (TDIF) and its cognate receptor, PHLOEM INTERCALATED WITH XYLEM (PXY). In this review, we explore the literature that describes signalling components, phytohormones and transcription factors that interact with these two central factors, to control the varying outputs required in vascular tissues for normal organization and elaboration of plant vascular tissue.

The role of auxin signaling in early embryo pattern formation.

Pattern formation of the early Arabidopsis embryo generates precursors to all major cell types, and is profoundly controlled by the signaling molecule auxin. Here we discuss recent milestones in our understanding of auxin-dependent embryo patterning. Auxin biosynthesis, transport and response mechanisms interact to generate local auxin accumulation in the early embryo. New auxin-dependent reporters help identifying these sites, while atomic structures of transcriptional response mediators help explain the diverse outputs of auxin signaling. Key auxin outputs are control of cell identity and cell division orientation, and progress has been made towards understanding the cellular basis of each. Importantly, a number of studies have combined computational modeling and experiments to analyze the developmental role, genetic circuitry and molecular mechanisms of auxin-dependent cell division control.

Plant development. Integration of growth and patterning during vascular tissue formation in Arabidopsis.

Coordination of cell division and pattern formation is central to tissue and organ development, particularly in plants where walls prevent cell migration. Auxin and cytokinin are both critical for division and patterning, but it is unknown how these hormones converge upon tissue development. We identify a genetic network that reinforces an early embryonic bias in auxin distribution to create a local, nonresponding cytokinin source within the root vascular tissue. Experimental and theoretical evidence shows that these cells act as a tissue organizer by positioning the domain of oriented cell divisions. We further demonstrate that the auxin-cytokinin interaction acts as a spatial incoherent feed-forward loop, which is essential to generate distinct hormonal response zones, thus establishing a stable pattern within a growing vascular tissue.

Ring chromosome formation as a novel escape mechanism in patients with inverted duplication and terminal deletion.

Ring chromosomes are rare cytogenetic findings and are associated at phenotypic level with mental retardation and congenital abnormalities. Features specific for ring chromosome syndromes often overlap with the features of terminal deletions for the corresponding chromosomes. Here, we report a case of a ring chromosome 14 which was identified by conventional cytogenetics and shown to have a terminal deletion and an additional inverted duplication with a triplication by using large insert clone and oligo array-comparative genomic hybridization (array-CGH), fluorescence in situ hybridization (FISH) and multiplex ligation-dependent probe amplification (MLPA). The combination of an inverted duplication with a terminal deletion in a ring chromosome is of special interest for the described syndromes of chromosome 14. The presented findings might explain partly overlapping clinical features described in terminal deletion, duplication and ring chromosome 14 cases, as these rearrangements can be easily overlooked when performing GTG-banding only. Furthermore, we suggest that ring chromosome formation can act as an alternative chromosome rescue next to telomere healing and capture, particularly for acrocentric chromosomes. To our knowledge, this is the first time an inverted duplication with a terminal deletion in a ring chromosome is identified and characterized using high-resolution molecular karyotyping. Systematic evaluation of ring chromosomes by array-CGH might be especially useful in distinguishing cases with a duplication/deletion from those with a deletion only.

Appendix in children with cystic fibrosis: US features.

PURPOSE: To evaluate the ultrasonographic (US) appearance of the appendix in children with cystic fibrosis but who were asymptomatic for appendicitis. MATERIALS AND METHODS: Between March 2001 and March 2002, 31 children (14 boys, 17 girls; mean age, 9.5 years; range, 2-16 years) with cystic fibrosis underwent graded-compression US of the appendix. The recordings were analyzed in consensus by two radiologists specialized in US. The overall appendiceal diameter and change in diameter during graded compression, wall dimensions, contents of material in the lumen, and periappendicular fat were evaluated. The exclusion criterion was abdominal pain at the time of investigation. RESULTS: In all but one patient, the appendix was visualized with US. The diameter of the appendix ranged from 4.0 to 14.5 mm (mean, 8.3 mm). In 25 patients (83.3%), the appendix measured more than 6.0 mm. In six patients, the diameter of the appendix changed when graded compression was applied. Mucoid material was found in the lumen in 27 of 30 patients. No wall thickening occurred, and concentric layer structures of the wall were intact. No involvement of the neighboring mesenteric or omental fat was encountered. CONCLUSION: The appendiceal diameter was enlarged in the majority of children examined. The lumen contained mucoid contents. Therefore, the diameter of the appendix alone may not be a parameter for diagnosing appendicitis in patients with cystic fibrosis.