Cleft Structure Research Articles

Are cleft sentence structures more difficult to process?

This study compares the processing of cleft structures against that of monoclausal sentences using event-related potential (ERP). We aim to understand how syntactic complexity is processed by comparing the neural response to cleft and single-clause sentences with identical verb phrases, controlling for verb bias frequency effects. Sixty participants were tested, and we presented 100 cleft and 100 monoclausal sentences, balanced for active and passive verb usage. We examined the P600 component, an ERP associated with syntactic complexity, to assess the processing of cleft structures. Results showed that cleft structures incur a greater processing load, as indicated by a larger P600, compared to monoclausal sentences. The P600 response indicates that processing cleft sentences requires additional syntactic operations, consistent with behavioral studies showing that clinical populations have difficulty comprehending complex sentences.

Transsynaptic Assemblies Link Domains of Presynaptic and Postsynaptic Intracellular Structures across the Synaptic Cleft.

The chemical synapse is a complex machine separated into three parts: presynaptic, postsynaptic, and cleft. Super-resolution light microscopy has revealed alignment of presynaptic vesicle release machinery and postsynaptic neurotransmitter-receptors and scaffolding components in synapse spanning nanocolumns. Cryo-electron tomography confirmed that postsynaptic glutamate receptor-like structures align with presynaptic structures in proximity to synaptic vesicles into transsynaptic assemblies. In our electron tomographic renderings, nearly all transcleft structures visibly connect to intracellular structures through transmembrane structures to form transsynaptic assemblies, potentially providing a structural basis for transsynaptic alignment. Here, we describe the patterns of composition, distribution, and interactions of all assemblies spanning the synapse by producing three-dimensional renderings of all visibly connected structures in excitatory and inhibitory synapses in dissociated rat hippocampal neuronal cultures of both sexes prepared by high-pressure freezing and freeze-substitution. The majority of transcleft structures connect to material in both presynaptic and postsynaptic compartments. We found several instances of assemblies connecting to both synaptic vesicles and postsynaptic density scaffolding. Each excitatory synaptic vesicle within 30 nm of the active zone contacts one or more assembly. Further, intracellular structures were often shared between assemblies, entangling them to form larger complexes or association domains, often in small clusters of vesicles. Our findings suggest that transsynaptic assemblies physically connect the three compartments, allow for coordinated molecular organization, and may combine to form specialized functional association domains, resembling the light-level nanocolumns.SIGNIFICANCE STATEMENT A recent tomographic study uncovered that receptor-like cleft structures align across the synapse. These aligned structures were designated as transsynaptic assemblies and demonstrate the coordinated organization of synaptic transmission molecules between compartments. Our present tomographic study expands on the definition of transsynaptic assemblies by analyzing the three-dimensional distribution and connectivity of all cleft-spanning structures and their connected intracellular structures. While one-to-one component alignment occurs across the synapse, we find that many assemblies share components, leading to a complex entanglement of assemblies, typically around clusters of synaptic vesicles. Transsynaptic assemblies appear to form domains which may be the structural basis for alignment of molecular nanodomains into synapse spanning nanocolumns described by super-resolution light microscopy.

Canonicity Effect on Sentence Processing of Persian-speaking Broca's Patients.

Fundamental notions of mapping hypothesis and canonicity were scrutinized in Persian-speaking aphasics. To this end, the performance of four age-, education-, and gender matched Persian-speaking Broca's patients and eight matched healthy controls in diverse complex structures were compared via the conduction of two tasks of syntactic comprehension and grammaticality judgment. The tested structures included subject agentive, agentive passive, object experience, subject experience, subject cleft, and object cleft constructions. Our results, while corroborating the predictions of the mapping hypothesis, showed that in structures, in which linguistic elements were substituted and dislocated out of their canonical syntactic positions, namely, agentive passive, subject experiencer, object experiencer, and object cleft constructions, Broca's problems escalated. In contrast, in those structures whose constituent concatenations were aligned with canonical syntactic structures, namely subject agentive, and cleft structures, patients had above the chance performance. Ultimately, the theoretical and clinical implications of the study were discussed. The number of predicates in a sentence, predicate types (psychological and agentive), as well as semantic heuristics and canonicity all by all could be regarded as the major culprits for aphasics' poor performance.

Towards the copular status of clefts—Evidence from diachrony

Abstract This paper draws attention to a robust grammatical change trajectory, here dubbed the copula-to-cleft pathway. We show that the emergence of the copular clause construction tends to lead to the emergence of the cleft construction, and the decline of one tends to be in tandem with the other. We further propose that the above pattern follows from a syntactic treatment that derives the cleft structure from a copular clause. Such copular syntax can be further combined with a semantic analysis where the focus interpretation of clefts is computed based on a copular structure.

Propagation and Separation of Downslope Gravity Currents over Rigid and Emergent Vegetation Patches in Linearly Stratified Environments

Large eddy simulation (combined with the mixture model) and laboratory experiment were used to investigate the impact of emergent and rigid vegetation on the dynamics of downslope gravity currents in stratified environments. The reliability of the numerical model was assessed with the corresponding laboratory measurements. The results show that the vegetation cylinders lead to severe lateral non-uniformity of the current front, causing more evident lobe and cleft structures. In stratified environments, the smaller driving force leads to less propagating velocity until the current separates from the slope. The transition point (from acceleration to deceleration phases) of current velocity appears earlier as the vegetation becomes denser. The peak value of the bulk entrainment coefficient Ebuik is inversely proportional to the vegetation density, while the final converged value of Ebuik is proportional to the vegetation density. Vegetation patches make the degree of fluctuation of the instantaneous entrainment coefficient Einst more intense, and even negative values appear locally, indicating that the gravity current is detrained into the ambient fluid. The velocity profiles of gravity current develop multi-peak patterns in stratified environments due to fingering intrusive patterns. Our analysis reveals that as the vegetation density increases, the generated wakes behind vegetation cylinders increase local entrainment and mixing, causing the density of current flow from vegetation to decrease and reach the neutral buoyancy layer of ambient fluids earlier, finally leading to a smaller separation depth.

Diagnostic value of computed tomography in Eustachian tube dysfunction

ObjectiveInvestigate radiological findings on temporal bone computed tomography, which are associated with obstructive Eustachian tube dysfunction and determine its diagnostic validity. MethodsThe present study was conducted as a prospective, cross-sectional case series study in a tertiary referral center. Forty patients with clinically diagnosed unilateral Eustachian tube dysfunction and older than 16 years old underwent pre interventional radiological assessment by temporal bone computed tomography while performing a Valsalva-maneuvre to enhance visualization of Eustachian tube lumen. The Eustachian tubes were assessed for intersite morphological differences, presence of mucus in the lumen or middle ear cleft and secretion retention or mucosal swelling in the adjacent sinuses. Image analyses and radiological statements about the side of pathology were delivered blinded to the clinical diagnoses. ResultsThe radiologic detection of mucus/mucosal edema in Eustachian tube or adjacent middle ear cleft structures was associated with the pathological side (t (1, N = 40) = 3.60, p = 0.001 < 0.05). On the contrary, there is no association between radiological findings of sinonasal disease and side of Eustachian tube dysfunction (x2 (1, N = 40) = .00, p = 1.00 > 0.05). The diagnostic value of radiologic assessment in Eustachian tube dysfunction has a sensitivity and specificity of 52,5 and 97,5% respectively. ConclusionThe sensitivity of radiologic assessment is rather low, and hence it is inappropriate as a screening tool for Eustachian tube dysfunction in routine clinical practice. In the case of present CT-scans of the temporal bone, the focus should be laid on the detection of mucus in the Eustachian tube or adjacent structures, as a predictor of disease.

The grammaticalization of term focus structures in Chadic languages: A case of microvariation

Abstract This paper argues that the Chadic languages Bura, South Marghi, Hausa, and Guruntum show different stages of the assumed grammaticalization path from bi-clausal cleft structures to mono-clausal constructions for the expression of term focus. This development is characterized by several syntactic and semantic changes, i.e. the reinterpretation of the cleft copula into a focus marker, the loss of the exhaustive inference typically associated with clefts, as well as the loss of syntactic indicators of embedded structures. Based on a microvariational comparison of the four languages, the paper hypothesizes that clefts are diachronically abandoned in favour of mono-clausal focus structures.

Documenting the Ikpana interrogative system

Abstract This article provides a comprehensive treatment of the interrogative system of Ikpana (ISO 639-3: lgq), an endangered language spoken in the southeastern part of Ghana’s Volta region. The article features a description and analysis of both the morphosyntax and intonation of questions in the language. Polar questions in Ikpana are associated with dedicated prosodic patterns and may be segmentally marked. As for wh- interrogatives, Ikpana allows for optional wh- movement. Interrogative expressions may appear clause-internally in their base-generated positions or in the left periphery followed by one of two optionally droppable particles with distinct syntactic properties. In this way, wh- movement structures are either focus-marked constructions or cleft structures depending on the accompanying particle. We identify an interesting wh- movement asymmetry – unlike all other wh- movement structures, ‘how’ questions may not be formed via the focus-marked or cleft strategy. We document a number of other attested wh- structures in the language, including long-distance wh- movement, partial wh- movement, long-distance wh- in-situ, and multiple wh- questions. We argue that by allowing our documentation efforts to be shaped and guided by theoretically driven research questions, we reach deeper levels of description than would have been possible if approached from a purely descriptive-documentary perspective.

Experimental study on the origin of lobe-cleft structures in a sand storm

Lobes and clefts are characteristic structures at the front of sand storms. In this paper, their original formation mechanism and geometric features are studied experimentally and theoretically. A rotatable lock-exchange tank is utilized to avoid the strong local disturbances existing in the conventional horizontal apparatus, and the original lobe size is selected as the dominant spanwise wavelength by a statistical method instead of the mean lobe size used in the literature. It is shown that at the initial formation stage, the measured lobe sizes for different tank geometries and density differences (or Atwood numbers) have a 1/3 scaling law with the Grashof number (Gr) as predicted by a Rayleigh–Taylor (RT) model, especially at moderate Gr range, and substantially depend on the diffusion effect represented by the Schmidt number. Furthermore, using turbulent Schmidt number and eddy viscosity for atmosphere in the RT model predicts large scale dominant lobes, whose sizes agree qualitatively with those observed in a real sand storm, revealing that the underlying control mechanism for these lobe and cleft structures is intrinsically related to the RT instability.

Structural basis for the core-mannan biosynthesis of cell wall fungal-type galactomannan in Aspergillus fumigatus

Fungal cell walls and their biosynthetic enzymes are potential targets for novel antifungal agents. Recently, two mannosyltransferases, namely core-mannan synthases A (CmsA/Ktr4) and B (CmsB/Ktr7), were found to play roles in the core-mannan biosynthesis of fungal-type galactomannan. CmsA/Ktr4 is an α-(1→2)-mannosyltransferase responsible for α-(1→2)-mannan biosynthesis in fungal-type galactomannan, which covers the cell surface of Aspergillus fumigatus Strains with disrupted cmsA/ktr4 have been shown to exhibit strongly suppressed hyphal elongation and conidiation alongside reduced virulence in a mouse model of invasive aspergillosis, indicating that CmsA/Ktr4 is a potential novel antifungal candidate. In this study we present the 3D structures of the soluble catalytic domain of CmsA/Ktr4, as determined by X-ray crystallography at a resolution of 1.95 Å, as well as the enzyme and Mn2+/GDP complex to 1.90 Å resolution. The CmsA/Ktr4 protein not only contains a highly conserved binding pocket for the donor substrate, GDP-mannose, but also has a unique broad cleft structure formed by its N- and C-terminal regions and is expected to recognize the acceptor substrate, a mannan chain. Based on these crystal structures, we also present a 3D structural model of the enzyme-substrate complex generated using docking and molecular dynamics simulations with α-Man-(1→6)-α-Man-(1→2)-α-Man-OMe as the model structure for the acceptor substrate. This predicted enzyme-substrate complex structure is also supported by findings from single amino acid substitution CmsA/Ktr4 mutants expressed in ΔcmsA/ktr4 A. fumigatus cells. Taken together, these results provide basic information for developing specific α-mannan biosynthesis inhibitors for use as pharmaceuticals and/or pesticides.

Resumption as a sluicing source in Saudi Arabic: Evidence from sluicing with prepositional phrases

This paper reports the results of three acceptability judgment experiments on Saudi Arabic elliptical questions (sluicing) with prepositional phrases. We show that in standard cases of merger type sluicing and contrastive sluicing there is no penalty for leaving out the preposition. Under an analysis of sluicing with syntactic identity between antecedent and ellipsis site, such examples require preposition stranding in the ellipsis site. We call this pattern OPUS, which the reader is invited to interpret as an abbreviation, depending on their theoretical predilections, as Ostensible P-stranding Under Sluicing or as Omission of Preposition Under Sluicing. Our findings show that Saudi Arabic violates Merchant’s (2001) second form identity generalization. Further experiments reveal that the status of the examples depends on the status of the most acceptable synonymous source within the ellipsis site; in particular, when neither a cleft structure nor a resumptive structure are grammatically available in the ellipsis site, the acceptability of OPUS decays. We interpret this as evidence that there is syntactic structure at the ellipsis site and that the wh-remnant in these elliptical questions can – and sometimes must – relate to a resumptive pronoun in the ellipsis site.

On the interpretation and processing of exhaustivity: Evidence of variation in English and French clefts

One outstanding issue in the analysis of the meaning of clefts concerns the source of the exhaustive inference they convey. Conventionally-coded semantic accounts predict that this inference is robust and will arise regardless of contextual variation while allowing for cross-linguistic variation. On the contrary, non-conventionally-coded pragmatic accounts predict exhaustivity to be more variable within a language, including cases where it can be cancelled, although (potentially) the inference will be more stable across languages. This article presents an original empirical perspective on the debate by looking both at the interpretative and the processing properties of English compared to French clefts. The combination of offline and online measures reported here show crucial and surprising differences within and across the two languages, findings which are unexpected under all current theories of clefts' meaning. We discuss a preliminary sketch for an analysis, which proposes that the differences between French and English are due to the way the existential presupposition derived from the cleft structure interacts with context (cf. Pollard and Yasavul, in press; De Veaugh-Geiss et al., 2018).

Noncritical Signaling Role of a Kinase–Receptor Interaction Surface in the Escherichia coli Chemosensory Core Complex

In Escherichia coli chemosensory arrays, transmembrane receptors, a histidine autokinase CheA, and a scaffolding protein CheW interact to form an extended hexagonal lattice of signaling complexes. One interaction, previously assigned a crucial signaling role, occurs between chemoreceptors and the CheW-binding P5 domain of CheA. Structural studies showed a receptor helix fitting into a hydrophobic cleft at the boundary between P5 subdomains. Our work aimed to elucidate the in vivo roles of the receptor–P5 interface, employing as a model the interaction between E. coli CheA and Tsr, the serine chemoreceptor. Crosslinking assays confirmed P5 and Tsr contacts in vivo and their strict dependence on CheW. Moreover, the P5 domain only mediated CheA recruitment to polar receptor clusters if CheW was also present. Amino acid replacements at CheA.P5 cleft residues reduced CheA kinase activity, lowered serine response cooperativity, and partially impaired chemotaxis. Pseudoreversion studies identified suppressors of P5 cleft defects at other P5 groove residues or at surface-exposed residues in P5 subdomain 1, which interacts with CheW in signaling complexes. Our results indicate that a high-affinity P5–receptor binding interaction is not essential for core complex function. Rather, P5 groove residues are probably required for proper cleft structure and/or dynamic behavior, which likely impact conformational communication between P5 subdomains and the strong binding interaction with CheW that is necessary for kinase activation. We propose a model for signal transmission in chemotaxis signaling complexes in which the CheW–receptor interface plays the key role in conveying signaling-related conformational changes from receptors to the CheA kinase.

Chinese cleft structures and the dynamics of processing

AbstractThis paper addresses the challenge of Chinese cleft structures, involving a pairing of the particles shi and de, which in different combinations display a variety of focus‐related effects and different potentials for ambiguity: clefts and pseudo‐clefts in particular differ only in order of the elements. We argue that retaining conventional assumptions necessarily involves positing unrelated structures and multiple ambiguities, leaving the systematicity of variation unexplained; and we go on to argue that it is only by turning to a dynamic framework in which syntax is defined as mechanisms for incremental build‐up of interpretation that an integrated characterisation of these effects is made possible. Adopting the Dynamic Syntax framework (Cann et al 2005), we argue that shi and de induce procedures for incremental build‐up of construal which feed and can be fed by other such procedures; and we show how the array of effects both in clefts and pseudo‐clefts can be shown to follow from the dynamics of building up interpretation reflecting online processing.

Lobe‐cleft instability in the buoyant gravity current generated by estuarine outflow

AbstractGravity currents represent a broad class of geophysical flows including turbidity currents, powder avalanches, pyroclastic flows, sea breeze fronts, haboobs, and river plumes. A defining feature in many gravity currents is the formation of three‐dimensional lobes and clefts along the front and researchers have sought to understand these ubiquitous geophysical structures for decades. The prevailing explanation is based largely on early laboratory and numerical model experiments at much smaller scales, which concluded that lobes and clefts are generated due to hydrostatic instability exclusively in currents propagating over a nonslip boundary. Recent studies suggest that frontal dynamics change as the flow scale increases, but no measurements have been made that sufficiently resolve the flow structure in full‐scale geophysical flows. Here we use thermal infrared and acoustic imaging of a river plume to reveal the three‐dimensional structure of lobes and clefts formed in a geophysical gravity current front. The observed lobes and clefts are generated at the front in the absence of a nonslip boundary, contradicting the prevailing explanation. The observed flow structure is consistent with an alternative formation mechanism, which predicts that the lobe scale is inherited from subsurface vortex structures.

The impact of focus on pronoun resolution in native and non-native sentence comprehension

Non-native speakers’ sensitivity to discourse-level cues in pronoun interpretation has not been widely researched. We carried out three antecedent-choice questionnaire experiments which investigate the impact of focus on within-sentence pronoun resolution in native and non-native speakers of German and native speakers of Russian. Focus was realized via cleft structures and focus-sensitive particles (FSPs). Findings show a clear difference between native and non-native speakers that is not attributable to first language (L1) influence. Native speakers of German and Russian were less likely to resolve the pronoun to an antecedent in focus via a cleft compared to a non-focused antecedent in the same position (the ‘anti-focus effect’). Unlike the native speakers, non-native speakers did not show an anti-focus effect with clefts but showed a tendency to resolve a pronoun to an antecedent appearing with an FSP. We argue that non-native speakers do not always complete a detailed analysis of the information structural cues when seeking an antecedent and may instead be influenced by surface-level cues that highlight certain antecedents.

Secondary Structure Preferences of the Anthrax Toxin Protective Antigen Translocase

In order for many proteins to move across hydrophobic membrane bilayers, they must be unfolded and translocated by a membrane-embedded channel. These translocase channels interact with the substrate proteins they translocate via hydrophobic pore loops and cleft structures called clamps. The molecular basis for how clamps facilitate unfolding and translocation is poorly understood. Anthrax toxin is composed of three proteins, a translocase channel-forming subunit, called protective antigen (PA), and two substrate proteins, called lethal factor (LF) and edema factor. Oligomeric PA forms a large channel that contains three types of polypeptide clamp sites: an α clamp, a phenylalanine clamp, and a charge clamp. Currently, it is thought that these clamp sites operate allosterically and promote translocation via an allosteric helix compression mechanism. Here, we report on the substrate secondary structure dependence of the PA channel. Peptides derived from regions of LF with high α-helical content bound cooperatively, but those derived from β-sheet regions in LF did not, suggesting that an allosteric site preferentially recognizes α-helical structure over β-sheet structure. Peptides derived from helical sites in LF showed increasingly longer single-channel blockades as a function of peptide concentration, a result that was consistent with stronger clamping behavior and reduced backsliding. Moreover, peptides derived from helical regions of LF translocated more efficiently than peptides derived from β-sheet regions of LF. Overall, in support of the allosteric helix compression model, we find that the channel prefers α-helical sequences over β-sheet sequences.

Activation of Wnt Signaling in Cortical Neurons Enhances Glucose Utilization through Glycolysis

The Wnt signaling pathway is critical for a number of functions in the central nervous system, including regulation of the synaptic cleft structure and neuroprotection against injury. Deregulation of Wnt signaling has been associated with several brain pathologies, including Alzheimer's disease. In recent years, it has been suggested that the Wnt pathway might act as a central integrator of metabolic signals from peripheral organs to the brain, which would represent a new role for Wnt signaling in cell metabolism. Energy metabolism is critical for normal neuronal function, which mainly depends on glucose utilization. Brain energy metabolism is important in almost all neurological disorders, to which a decrease in the capacity of the brain to utilize glucose has been linked. However, little is known about the relationship between Wnt signaling and neuronal glucose metabolism in the cellular context. In the present study, we found that acute treatment with the Wnt3a ligand induced a large increase in glucose uptake, without changes in the expression or localization of glucose transporter type 3. In addition, we observed that Wnt3a treatment increased the activation of the metabolic sensor Akt. Moreover, we observed an increase in the activity of hexokinase and in the glycolytic rate, and both processes were dependent on activation of the Akt pathway. Furthermore, we did not observe changes in the activity of glucose-6-phosphate dehydrogenase or in the pentose phosphate pathway. The effect of Wnt3a was independent of both the transcription of Wnt target genes and synaptic effects of Wnt3a. Together, our results suggest that Wnt signaling stimulates glucose utilization in cortical neurons through glycolysis to satisfy the high energy demand of these cells.

Perinatal exposure to lead (Pb) induces ultrastructural and molecular alterations in synapses of rat offspring.

Lead (Pb), environmentally abundant heavy-metal pollutant, is a strong toxicant for the developing central nervous system. Pb intoxication in children, even at low doses, is found to affect learning and memorizing, with devastating effects on cognitive function and intellectual development. However, the precise mechanism by which Pb impairs synaptic plasticity is not fully elucidated. The purpose of this study was to investigate the effect of pre- and neonatal exposure to low dose of Pb (with Pb concentrations in whole blood below 10μg/dL) on the synaptic structure and the pre- and postsynaptic proteins expression in the developing rat brain. Furthermore, the level of brain-derived neurotrophic factor (BDNF) was analyzed. Pregnant female Wistar rats received 0.1% lead acetate (PbAc) in drinking water from the first day of gestation until weaning of the offspring, while the control animals received drinking water. During the feeding of pups, mothers from the Pb-group were continuously receiving PbAc. Pups of both groups were weaned at postnatal day 21 and then until postnatal day 28 received only drinking water. 28-day old pups were sacrificed and the ultrastructural changes as well as expression of presynaptic (VAMP1/2, synaptophysin, synaptotagmin-1, SNAP25, syntaxin-1) and postsynaptic (PSD-95) proteins were analyzed in: forebrain cortex, cerebellum and hippocampus. Our data revealed that pre- and neonatal exposure to low dose of Pb promotes pathological changes in synapses, including nerve endings swelling, blurred and thickened synaptic cleft structure as well as enhanced density of synaptic vesicles in the presynaptic area. Moreover, synaptic mitochondria were elongated, swollen or shrunken in Pb-treated animals. These structural abnormalities were accompanied by decrease in the level of key synaptic proteins: synaptotagmin-1 in cerebellum, SNAP25 in hippocampus and syntaxin-1 in cerebellum and hippocampus. In turn, increased level of synaptophysin was noticed in the cerebellum, while the expression of postsynaptic PSD-95 was significantly decreased in forebrain cortex and cerebellum, and raised in hippocampus. Additionally, we observed the lower level of BDNF in all brain structures in comparison to control animals. In conclusion, perinatal exposure to low doses of Pb caused pathological changes in nerve endings associated with the alterations in the level of key synaptic proteins. All these changes can lead to synaptic dysfunction, expressed by the impairment of the secretory mechanism and thereby to the abnormalities in neurotransmission as well as to the neuronal dysfunction.

Emergence of dorsal-ventral polarity in ESC-derived retinal tissue.

We previously demonstrated that mouse embryonic stem cell (mESC)-derived retinal epithelium self-forms an optic cup-like structure. In the developing retina, the dorsal and ventral sides differ in terms of local gene expression and morphological features. This aspect has not yet been shown in vitro Here, we demonstrate that mESC-derived retinal tissue spontaneously acquires polarity reminiscent of the dorsal-ventral (D-V) patterning of the embryonic retina. Tbx5 and Vax2 were expressed in a mutually exclusive manner, as seen in vivo Three-dimensional morphometric analysis showed that the in vitro-formed optic cup often contains cleft structures resembling the embryonic optic fissure. To elucidate the mechanisms underlying the spontaneous D-V polarization of mESC-derived retina, we examined the effects of patterning factors, and found that endogenous BMP signaling plays a predominant role in the dorsal specification. Further analysis revealed that canonical Wnt signaling, which was spontaneously activated at the proximal region, acts upstream of BMP signaling for dorsal specification. These observations suggest that D-V polarity could be established within the self-formed retinal neuroepithelium by intrinsic mechanisms involving the spatiotemporal regulation of canonical Wnt and BMP signals.