Analysis of Fusobacterium persistence and antibiotic response in colorectal cancer

Colorectal cancers comprise a complex mixture of malignant cells, nontransformed cells, and microorganisms. Fusobacterium nucleatum is among the most prevalent bacterial species in colorectal cancer tissues. Here we show that colonization of human colorectal cancers with Fusobacterium and its associated microbiome-including Bacteroides, Selenomonas, and Prevotella species-is maintained in distal metastases, demonstrating microbiome stability between paired primary and metastatic tumors. In situ hybridization analysis revealed that Fusobacterium is predominantly associated with cancer cells in the metastatic lesions. Mouse xenografts of human primary colorectal adenocarcinomas were found to retain viable Fusobacterium and its associated microbiome through successive passages. Treatment of mice bearing a colon cancer xenograft with the antibiotic metronidazole reduced Fusobacterium load, cancer cell proliferation, and overall tumor growth. These observations argue for further investigation of antimicrobial interventions as a potential treatment for patients with Fusobacterium-associated colorectal cancer.

Metabolic plasticity in stem cell homeostasis and differentiation

Plasticity in energy metabolism allows stem cells to match the divergent demands of self-renewal and lineage specification. Beyond a role in energetic support, new evidence implicates nutrient-responsive metabolites as mediators of crosstalk between metabolic flux, cellular signaling, and epigenetic regulation of cell fate. Stem cell metabolism also offers a potential target for controlling tissue homeostasis and regeneration in aging and disease. In this Perspective, we cover recent progress establishing an emerging relationship between stem cell metabolism and cell fate control.

Repair of acute myocardial infarction by human stemness factors induced pluripotent stem cells

BACKGROUND

Nuclear reprogramming provides an emerging strategy to produce embryo-independent pluripotent stem cells from somatic tissue. Induced pluripotent stem cells (iPS) demonstrate aptitude for de novo cardiac differentiation, yet their potential for heart disease therapy has not been tested.

METHODS AND RESULTS

In this study, fibroblasts transduced with human stemness factors OCT3/4, SOX2, KLF4, and c-MYC converted into an embryonic stem cell-like phenotype and demonstrated the ability to spontaneously assimilate into preimplantation host morula via diploid aggregation, unique to bona fide pluripotent cells. In utero, iPS-derived chimera executed differentiation programs to construct normal heart parenchyma patterning. Within infarcted hearts in the adult, intramyocardial delivery of iPS yielded progeny that properly engrafted without disrupting cytoarchitecture in immunocompetent recipients. In contrast to parental nonreparative fibroblasts, iPS treatment restored postischemic contractile performance, ventricular wall thickness, and electric stability while achieving in situ regeneration of cardiac, smooth muscle, and endothelial tissue.

CONCLUSIONS

Fibroblasts reprogrammed by human stemness factors thus acquire the potential to repair acute myocardial infarction, establishing iPS in the treatment of heart disease.

Internal Ca2+ mobilization is altered in fibroblasts from patients with Alzheimer disease

The recent demonstration of K+ channel dysfunction in fibroblasts from Alzheimer disease (AD) patients and past observations of Ca(2+)-mediated K+ channel modulation during memory storage suggested that AD, which is characterized by memory loss and other cognitive deficits, might also involve dysfunction of intracellular Ca2+ mobilization. Bombesin-induced Ca2+ release, which is inositol trisphosphate-mediated, is shown here to be greatly enhanced in AD fibroblasts compared with fibroblasts from control groups. Bradykinin, another activator of phospholipase C, elicits similar enhancement of Ca2+ signaling in AD fibroblasts. By contrast, thapsigargin, an agent that releases Ca2+ by direct action on the endoplasmic reticulum, produced no differences in Ca2+ increase between AD and control fibroblasts. Depolarization-induced Ca2+ influx data previously demonstrated the absence of between-group differences of Ca2+ pumping and/or buffering. There was no correlation between the number of passages in tissue culture and the observed Ca2+ responses. Furthermore, cells of all groups were seeded and analyzed at the same densities. Radioligand binding experiments indicated that the number and affinity of bombesin receptors cannot explain the observed differences. These and previous observations suggest that the differences in bombesin and bradykinin responses in fibroblasts and perhaps other cell types are likely to be due to alteration of inositol trisphosphate-mediated release of intracellular Ca2+.

ROUGH SHEATH2: a Myb protein that represses knox homeobox genes in maize lateral organ primordia

The regulation of members of the knotted1-like homeobox (knox) gene family is required for the normal initiation and development of lateral organs. The maize rough sheath2 (rs2) gene, which encodes a Myb-domain protein, is expressed in lateral organ primordia and their initials. Mutations in the rs2 gene permit ectopic expression of knox genes in leaf and floral primordia, causing a variety of developmental defects. Ectopic KNOX protein accumulation in rs2 mutants occurs in a subset of the normal rs2-expressing cells. This variegated accumulation of KNOX proteins in rs2 mutants suggests that rs2 represses knox expression through epigenetic means.

Gamma-ray emission concurrent with the nova in the symbiotic binary V407 Cygni

Novae are thermonuclear explosions on a white dwarf surface fueled by mass accreted from a companion star. Current physical models posit that shocked expanding gas from the nova shell can produce x-ray emission, but emission at higher energies has not been widely expected. Here, we report the Fermi Large Area Telescope detection of variable gamma-ray emission (0.1 to 10 billion electron volts) from the recently detected optical nova of the symbiotic star V407 Cygni. We propose that the material of the nova shell interacts with the dense ambient medium of the red giant primary and that particles can be accelerated effectively to produce pi(0) decay gamma-rays from proton-proton interactions. Emission involving inverse Compton scattering of the red giant radiation is also considered and is not ruled out.

The identification of CVP1 reveals a role for sterols in vascular patterning

Vascular cell axialization refers to the uniform alignment of vascular strands. In the Arabidopsis cotyledon vascular pattern1 (cvp1) mutant, vascular cells are not arranged in parallel files and are misshapen, suggesting that CVP1 has a role in promoting vascular cell polarity and alignment. Characterization of an allelic series of cvp1 mutations revealed additional functions of CVP1 in organ expansion and elongation. We identified CVP1 and found that it encodes STEROL METHYLTRANSFERASE2 (SMT2), an enzyme in the sterol biosynthetic pathway. SMT2 and the functionally redundant SMT3 act at a branch point in the pathway that mediates sterol and brassinosteroid levels. The SMT2 gene is expressed in a number of developing organs and is regulated by various hormones. As predicted from SMT2 enzymatic activity, the precursors to brassinosteroid are increased at the expense of sterols in cvp1 mutants, identifying a role for sterols in vascular cell polarization and axialization.

Light-regulated gene expression during maize leaf development

We have established schedules of expression during maize leaf development in light and darkness for the messenger RNAs (mRNAs) and polypeptides for ribulose 1,5-bisphosphate carboxylase (RuBPCase) subunits, phosphoenolpyruvate carboxylase (PEPCase), and the light-harvesting chlorophyll a/b-binding protein (LHCP). Levels of mRNAs were measured by hybridization with cloned probes, and proteins were measured by immunodetection on protein gel blots. The initial synthesis in leaves of all four mRNAs follows a light-independent schedule; illumination influences only the level to which each mRNA accumulates. The synthesis of RuBPCase small and large subunits and of PEPCase polypeptides also follows a light-independent schedule which is modified quantitatively by light. However, the accumulation of LHCP polypeptides absolutely requires illumination. The accumulation of each protein closely follows the accumulation of its mRNA during growth in light. Higher ratios of PEPCase and RuBPCase protein to mRNA occur during dark growth.

The extraneural distribution of gamma-hydroxybutyrate

gamma-Hydroxybutyrate has been found to be widely distributed in both neural and extraneural tissues in the rat. The kidney and brown fat have more than 10 times higher concentrations of gamma-hydroxybutyrate than does the brain. This observation suggests that gamma-hydroxybutyrate may participate in the metabolism of many organs, and that GABA may not be the precursor in extraneural tissues.

Genome-wide analysis of epigenetic silencing identifies BEX1 and BEX2 as candidate tumor suppressor genes in malignant glioma

Promoter hypermethylation and histone deacetylation are common epigenetic mechanisms implicated in the transcriptional silencing of tumor suppressor genes in human cancer. We treated two immortalized glioma cell lines, T98 and U87, and 10 patient-derived primary glioma cell lines with trichostatin A (TSA), a histone deacetylase inhibitor, or 5-aza-2'-deoxycytidine (5-AzaC), a DNA methyltransferase inhibitor, to comprehensively identify the cohort of genes reactivated through the pharmacologic reversal of these distinct but related epigenetic processes. Whole-genome microarray analysis identified genes induced by TSA (653) or 5-AzaC treatment (170). We selected a subset of reactivated genes that were markedly induced (greater than two-fold) after treatment with either TSA or 5-AzaC in a majority of glioma cell lines but not in cultured normal astrocytes. We then characterized the degree of promoter methylation and transcriptional silencing of selected genes in histologically confirmed human tumor and nontumor brain specimens. We identified two novel brain expressed genes, BEX1 and BEX2, which were silenced in all tumor specimens and exhibited extensive promoter hypermethylation. Viral-mediated reexpression of either BEX1 or BEX2 led to increased sensitivity to chemotherapy-induced apoptosis and potent tumor suppressor effects in vitro and in a xenograft mouse model. Using an integrated approach, we have established a novel platform for the genome-wide screening of epigenetically silenced genes in malignant glioma. This experimental paradigm provides a powerful new method for the identification of epigenetically silenced genes with potential function as tumor suppressors, biomarkers for disease diagnosis and detection, and therapeutically reversible modulators of critical regulatory pathways important in glioma pathogenesis.

The sterol methyltransferases SMT1, SMT2, and SMT3 influence Arabidopsis development through nonbrassinosteroid products

Plant sterols are structural components of cell membranes that provide rigidity, permeability, and regional identity to membranes. Sterols are also the precursors to the brassinosteroid signaling molecules. Evidence is accumulating that specific sterols have roles in pattern formation during development. COTYLEDON VASCULAR PATTERNING1 (CVP1) encodes C-24 STEROL METHYLTRANSFERASE2 (SMT2), one of three SMTs in Arabidopsis (Arabidopsis thaliana). SMT2 and SMT3, which also encodes a C-24 SMT, catalyze the reaction that distinguishes the synthesis of structural sterols from signaling brassinosteroid derivatives and are highly regulated. The deficiency of SMT2 in the cvp1 mutant results in moderate developmental defects, including aberrant cotyledon vein patterning, serrated floral organs, and reduced stature, but plants are viable, suggesting that SMT3 activity can substitute for the loss of SMT2. To test the distinct developmental roles of SMT2 and SMT3, we identified a transcript null smt3 mutant. Although smt3 single mutants appear wild type, cvp1 smt3 double mutants show enhanced defects relative to cvp1 mutants, such as discontinuous cotyledon vein pattern, and produce novel phenotypes, including defective root growth, loss of apical dominance, sterility, and homeotic floral transformations. These phenotypes are correlated with major alterations in the profiles of specific sterols but without significant alterations to brassinosteroid profiles. The alterations to sterol profiles in cvp1 mutants affect auxin response, demonstrated by weak auxin insensitivity, enhanced axr1 auxin resistance, ectopically expressed DR5:beta-glucuronidase in developing embryos, and defective response to auxin-inhibited PIN2-green fluorescent protein endocytosis. We discuss the developmental roles of sterols implied by these results.

Arabidopsis thickvein mutation affects vein thickness and organ vascularization, and resides in a provascular cell-specific spermine synthase involved in vein definition and in polar auxin transport

Polar auxin transport has been implicated in the induction of vascular tissue and in the definition of vein positions. Leaves treated with chemical inhibitors of polar auxin transport exhibited vascular phenotypes that include increased vein thickness and vascularization. We describe a recessive mutant, thickvein (tkv), which develops thicker veins in leaves and in inflorescence stems. The increased vein thickness is attributable to an increased number of vascular cells. Mutant plants have smaller leaves and shorter inflorescence stems, and this reduction in organ size and height is accompanied by an increase in organ vascularization, which appears to be attributable to an increase in the recruitment of cells into veins. Furthermore, although floral development is normal, auxin transport in the inflorescence stem is significantly reduced in the mutant, suggesting that the defect in auxin transport is responsible for the vascular phenotypes. In the primary root, the veins appear morphologically normal, but root growth in the tkv mutant is hypersensitive to exogenous cytokinin. The tkv mutation was found to reside in the ACL5 gene, which encodes a spermine synthase and whose expression is specific to provascular cells. We propose that ACL5/TKV is involved in vein definition (defining the boundaries between veins and nonvein regions) and in polar auxin transport, and that polyamines are involved in this process.

Effects of maximal exercise stress on left ventricular function in patients with coronary artery disease using first pass radionuclide angiocardiography: a rapid, noninvasive technique for determining ejection fraction and segmental wall motion

Angiographically determined changes in segmental wall motion (SWM) and ejection fraction (EF) are sensitive indices of left ventricular (LV) function. To compare the effects of exercise on LV function, first pass radionuclide angiocardiography was used before and during maximal upright bicycle stress in patients with nonsignificantly stenosed coronary arteries, and in those with greater than 75% stenosis. Gamma camera acquisitions were made in the 30 degree RAO projection using a 20 mCi I.V. bolus of 99mTc-pertechnetate. In the control group (seven normals, one nonsignificant (CAD) the EF significantly increased between rest and exercise (0.65 +/- 0.03 to 0.81 +/- 0.03 (mean +/- SEM), p less than 0.005). In this group SWM measured over the two anterior and two inferoposterior segments uniformly increased. In the 11 patients with a history of angina and significant coronary artery obstruction, the EF did not change in three and significantly decreased in the remaining eight (0.57 +/- 0.04 to 0.45 +/- 0.03, p less than 0.005). In all 11 patients SWM either decreased or did not increase in the areas supplied by the significantly stenosed coronary arteries. Upright maximal stress angiocardiography appears to be well-suited for diagnosing ischemic heart disease and localizing the area of ischemic dysfunction.

Cell position and light influence C4 versus C3 patterns of photosynthetic gene expression in maize

C4 plants such as maize partition photosynthetic activities in two morphologically distinct cell types, bundle sheath (BS) and mesophyll (M), which lie as concentric layers around veins. We show that both light and cell position relative to veins influence C4 photosynthetic gene expression. A pattern of gene expression characteristic of C3 plants [ribulose bisphosphate carboxylase (RuBPCase) and light-harvesting chlorophyll a/b binding protein in all photosynthetic cells] is observed in leaf-like organs such as husk leaves, which are sparsely vascularized. This pattern of gene expression reflects direct fixation of CO2 in the C3 photosynthetic pathway, as determined by O2 inhibition assays. Light induces a switch from C3-type to C4-type gene expression patterns in all leaves, primarily in cells that are close to a vein. We propose that light causes repression of RuBPCase expression in M cells, by a mechanism associated with the vascular system, and that this is an essential step in the induction of C4 photosynthesis.

Time domains of neuronal Ca2+ signaling and associative memory: steps through a calexcitin, ryanodine receptor, K+ channel cascade

Synaptic changes that underlie associative learning and memory begin with temporally related activity of two or more independent synaptic inputs to common postsynaptic targets. In turn, temporally related molecular events regulate cytosolic Ca2+ during progressively longer-lasting time domains. Associative learning behaviors of living animals have been correlated with changes of neuronal voltage-dependent K+ currents, protein kinase C-mediated phosphorylation and synthesis of the Ca2+ and GTP-binding protein, calexcitin (CE),and increased expression of the Ca2+-releasing ryanodine receptor (type II). These molecular events, some of which have been found to be dysfunctional in Alzheimer's disease, provide means of altering dendritic excitability and thus synaptic efficacy during induction, consolidation and storage of associative memory. Apparently, such stages of behavioral learning correspond to sequential differences of Ca2+ signaling that could occur in spatially segregated dendritic compartments distributed across brain structures, such as the hippocampus.

Synthesis of hybrid bacterial plasmids containing highly repeated satellite DNA

Hybrid plasmid molecules containing tandemly repeated Drosophila satellite DNA were constructed using a modification of the (dA)-(dT) homopolymer procedure of Lobban and Kaiser (1973). Recombinant plasmids recovered after transformation of recA bacteria contained 10% of the amount of satellite DNA present in the transforming molecules. The cloned plasmids were not homogenous in size. Recombinant plasmids isolated from a single colony contained populations of circular molecules which varied both in the length of the satellite region and in the poly(dA)-(dt) regions linking satellite and vector. While subcloning reduced the heterogeneity of these plasmid populations, continued cell growth caused further variations in the size of the repeated regions. Two different simple sequence satellites of Drosophila melanogaster (1.672 and 1.705 g/cm3) were unstable in both recA and recBC hosts and in both pSC101 and pCR1 vectors. We propose that this recA-independent instability of tandemly repeated sequences is due to unequal intramolecular recombination events in replicating DNA molecules, a mechanism analogous to sister chromatid exchange in eucaryotes.

Fathers' Perceived Reasons for Their Underrepresentation in Child Health Research and Strategies to Increase Their Involvement

Purpose Examine fathers' perceived reasons for their lack of inclusion in pediatric research and strategies to increase their participation. Description We conducted expert interviews with researchers and practitioners (N = 13) working with fathers to inform the development of an online survey. The survey-which measured fathers' perceived reasons for their underrepresentation in pediatric research, recommended recruitment venues, and research personnel and study characteristics valued by fathers-was distributed online and in-person to fathers. Assessment Respondents included 303 fathers. Over 80 % of respondents reported that fathers are underrepresented in pediatric research because they have not been asked to participate. Frequently recommended recruitment venues included community sports events (52 %), social service programs (48 %) and the internet (60 %). Compared with white fathers, more non-white fathers recommended public transit (19 % vs. 10 %, p = .02), playgrounds (16 % vs. 6 %, p = .007) and barber shops (34 % vs. 14 %, p < .0001) and fewer recommended doctors' offices (31 % vs. 43 %, p = .046) as recruitment venues. Compared with residential fathers (100 % resident with the target child), more non-residential fathers recommended social services programs (45 % vs. 63 %, p = .03) and public transit (10 % vs. 27 %, p = .001) and fewer recommended the workplace (17 % vs. 40 %, p = .002) as recruitment venues. Study brevity, perceived benefits for fathers and their families, and the credibility of the lead organization were valued by fathers. Conclusion Fathers' participation in pediatric research may increase if researchers explicitly invite father to participate, target father-focused recruitment venues, clearly communicate the benefits of the research for fathers and their families and adopt streamlined study procedures.

Disease-causing mitochondrial heteroplasmy segregated within induced pluripotent stem cell clones derived from a patient with MELAS

Mitochondrial diseases display pathological phenotypes according to the mixture of mutant versus wild-type mitochondrial DNA (mtDNA), known as heteroplasmy. We herein examined the impact of nuclear reprogramming and clonal isolation of induced pluripotent stem cells (iPSC) on mitochondrial heteroplasmy. Patient-derived dermal fibroblasts with a prototypical mitochondrial deficiency diagnosed as mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS) demonstrated mitochondrial dysfunction with reduced oxidative reserve due to heteroplasmy at position G13513A in the ND5 subunit of complex I. Bioengineered iPSC clones acquired pluripotency with multilineage differentiation capacity and demonstrated reduction in mitochondrial density and oxygen consumption distinguishing them from the somatic source. Consistent with the cellular mosaicism of the original patient-derived fibroblasts, the MELAS-iPSC clones contained a similar range of mtDNA heteroplasmy of the disease-causing mutation with identical profiles in the remaining mtDNA. High-heteroplasmy iPSC clones were used to demonstrate that extended stem cell passaging was sufficient to purge mutant mtDNA, resulting in isogenic iPSC subclones with various degrees of disease-causing genotypes. On comparative differentiation of iPSC clones, improved cardiogenic yield was associated with iPSC clones containing lower heteroplasmy compared with isogenic clones with high heteroplasmy. Thus, mtDNA heteroplasmic segregation within patient-derived stem cell lines enables direct comparison of genotype/phenotype relationships in progenitor cells and lineage-restricted progeny, and indicates that cell fate decisions are regulated as a function of mtDNA mutation load. The novel nuclear reprogramming-based model system introduces a disease-in-a-dish tool to examine the impact of mutant genotypes for MELAS patients in bioengineered tissues and a cellular probe for molecular features of individual mitochondrial diseases.

Intrinsic Endocardial Defects Contribute to Hypoplastic Left Heart Syndrome

Hypoplastic left heart syndrome (HLHS) is a complex congenital heart disease characterized by abnormalities in the left ventricle, associated valves, and ascending aorta. Studies have shown intrinsic myocardial defects but do not sufficiently explain developmental defects in the endocardial-derived cardiac valve, septum, and vasculature. Here, we identify a developmentally impaired endocardial population in HLHS through single-cell RNA profiling of hiPSC-derived endocardium and human fetal heart tissue with an underdeveloped left ventricle. Intrinsic endocardial defects contribute to abnormal endothelial-to-mesenchymal transition, NOTCH signaling, and extracellular matrix organization, key factors in valve formation. Endocardial abnormalities cause reduced cardiomyocyte proliferation and maturation by disrupting fibronectin-integrin signaling, consistent with recently described de novo HLHS mutations associated with abnormal endocardial gene and fibronectin regulation. Together, these results reveal a critical role for endocardium in HLHS etiology and provide a rationale for considering endocardial function in regenerative strategies.

VH1, a provascular cell-specific receptor kinase that influences leaf cell patterns in Arabidopsis

The formation of the venation pattern in leaves is ideal for examining signaling pathways that recognize and respond to spatial and temporal information, because the pattern is two-dimensional and heritable and the resulting veins influence the three-dimensional spatial organization of the surrounding differentiating leaf cell types. We identified a provascular/procambial cell-specific gene that encodes a Leu-rich repeat receptor kinase, which we named VASCULAR HIGHWAY1 (VH1). A change in the expression domain and level of VH1 marks the transition from an uncommitted provascular state to a committed procambial state in early vascular development. The coding sequence, expression pattern, and transgenic phenotypes together suggest that VH1 transduces extracellular spatial and temporal signals into downstream cell differentiation responses in provascular/procambial cells.

In vivo-like drug responses of human tumors growing in three-dimensional gel-supported primary culture

An in vitro test of cell sensitivity to drugs that indicates in vivo response is an important need in cancer therapy and cancer drug development. Toward this end, we previously developed a collagen gel-supported culture system for growth of human tumors. This three-dimensional culture system is general and grows tumors at high frequency directly from surgery or biopsy that maintain important in vivo properties in vitro, including tissue architecture. We report here that with autoradiographic techniques measuring cellular DNA synthesis the drug responses of individual cells within the tissue structure of in vitro-grown tumors can be determined. Twenty tumor classes, including all the major ones, have been measured in toto at greater than 50% frequency. Quantitative and qualitative results show increasing cell kill with rising cytotoxic drug concentration, differential drug sensitivities of multiple cell types within individual cultured tumors, differential sensitivities of a series of tumors of the same histopathological classification to a single drug, differential sensitivities of individual tumors to a series of drugs, and sensitivity patterns of various tumor types similar to the sensitivities found in vivo. Therefore, the results indicate that potentially important therapeutic data can be obtained from tumor specimens growing in vitro for the individual cancer patient as well as for rational and relevant screening for new agents active against human solid tumors.

iPS programmed without c-MYC yield proficient cardiogenesis for functional heart chimerism

RATIONALE

Induced pluripotent stem cells (iPS) allow derivation of pluripotent progenitors from somatic sources. Originally, iPS were induced by a stemness-related gene set that included the c-MYC oncogene.

OBJECTIVE

Here, we determined from embryo to adult the cardiogenic proficiency of iPS programmed without c-MYC, a cardiogenicity-associated transcription factor.

METHODS AND RESULTS

Transgenic expression of 3 human stemness factors SOX2, OCT4, and KLF4 here reset murine fibroblasts to the pluripotent ground state. Transduction without c-MYC reversed cellular ultrastructure into a primitive archetype and induced stem cell markers generating 3-germ layers, all qualifiers of acquired pluripotency. Three-factor induced iPS (3F-iPS) clones reproducibly demonstrated cardiac differentiation properties characterized by vigorous beating activity of embryoid bodies and robust expression of cardiac Mef2c, alpha-actinin, connexin43, MLC2a, and troponin I. In vitro isolated iPS-derived cardiomyocytes demonstrated functional excitation-contraction coupling. Chimerism with 3F-iPS derived by morula-stage diploid aggregation was sustained during prenatal heart organogenesis and contributed in vivo to normal cardiac structure and overall performance in adult tumor-free offspring.

CONCLUSIONS

Thus, 3F-iPS bioengineered without c-MYC achieve highest stringency criteria for bona fide cardiogenesis enabling reprogrammed fibroblasts to yield de novo heart tissue compatible with native counterpart throughout embryological development and into adulthood.

Leafbladeless1 is required for dorsoventrality of lateral organs in maize

The maize leafbladeless1 (lbl1) mutant displays a variety of leaf and plant phenotypes. The most extreme manifestation in the leaf is the formation of radially symmetric, abaxialized leaves due to a complete loss of adaxial cell types. Less severe phenotypes, resulting from a partial loss of adaxial cell identity, include the formation of ectopic laminae at the boundary between abaxialized, mutant sectors on the adaxial leaf surface and the bifurcation of leaves. Ectopic laminae and bifurcations arise early in leaf development and result in an altered patterning of the leaf along the proximodistal axis, or in complete duplication of the developing organ. Leaf-like lateral organs of the inflorescences and flowers show similar phenotypes. These observations suggest that Lbl1 is required for the specification of adaxial cell identity within leaves and leaf-like lateral organs. Lbl1 is also required for the lateral propagation of leaf founder cell recruitment, and plays a direct or indirect role in the downregulation of the homeobox gene, knotted1, during leaf development. Our results suggest that adaxial/abaxial asymmetry of lateral organs is specified in the shoot apical meristem, and that formation of this axis is essential for marginal, lateral growth and for the specification of points of proximodistal growth. Parallels between early patterning events during lateral organ development in plants and animals are discussed.