Facial analytics based on a coordinate extrapolation system (zFACE) for morphometric phenotyping of developing zebrafish.

Facial development requires a complex and coordinated series of cellular events that, when perturbed, can lead to structural birth defects. A quantitative approach to quickly assess morphological changes could address how genetic or environmental inputs lead to differences in facial shape and promote malformations. Here, we report on a method to rapidly analyze craniofacial development in zebrafish embryos using facial analytics based on a coordinate extrapolation system, termed zFACE. Confocal images capture facial structures and morphometric data are quantified based on anatomical landmarks present during development. The quantitative morphometric data can detect phenotypic variation and inform on changes in facial morphology. We applied this approach to show that loss of smarca4a in developing zebrafish leads to craniofacial anomalies, microcephaly and alterations in brain morphology. These changes are characteristic of Coffin-Siris syndrome, a rare human genetic disorder associated with mutations in SMARCA4. Multivariate analysis of zFACE data facilitated the classification of smarca4a mutants based on changes in specific phenotypic characteristics. Together, zFACE provides a way to rapidly and quantitatively assess the impact of genetic alterations on craniofacial development in zebrafish.

Polygenic risk impacts PDGFRA mutation penetrance in non-syndromic cleft lip and palate.

Non-syndromic cleft lip with or without cleft palate (NSCL/P) is a common, severe craniofacial malformation that imposes significant medical, psychosocial and financial burdens. NSCL/P is a multifactorial disorder with genetic and environmental factors playing etiologic roles. Currently, only 25% of the genetic variation underlying NSCL/P has been identified by linkage, candidate gene and genome-wide association studies. In this study, whole-genome sequencing and genome-wide genotyping followed by polygenic risk score (PRS) and linkage analyses were used to identify the genetic etiology of NSCL/P in a large three-generation family. We identified a rare missense variant in PDGFRA (c.C2740T; p.R914W) as potentially etiologic in a gene-based association test using pVAAST (P = 1.78 × 10-4) and showed decreased penetrance. PRS analysis suggested that variant penetrance was likely modified by common NSCL/P risk variants, with lower scores found among unaffected carriers. Linkage analysis provided additional support for PRS-modified penetrance, with a 7.4-fold increase in likelihood after conditioning on PRS. Functional characterization experiments showed that the putatively causal variant was null for signaling activity in vitro; further, perturbation of pdgfra in zebrafish embryos resulted in unilateral orofacial clefting. Our findings show that a rare PDGFRA variant, modified by additional common NSCL/P risk variants, have a profound effect on NSCL/P risk. These data provide compelling evidence for multifactorial inheritance long postulated to underlie NSCL/P and may explain some unusual familial patterns.

A protocol to evaluate epithelial regeneration after inducing cell loss in zebrafish larvae.

Epithelial tissues sustain barrier function by removing and replacing aberrant or unfit cells. Here, we describe approaches to evaluate epithelial restorative capacity after inducing cell loss in zebrafish larvae. We provide details to quantify morphological changes to the tail fin epithelium after cell loss, and instructions to interrogate changes in gene expression and proliferation associated with replacement of the lost cells. Together, this approach establishes an in vivo vertebrate model for the rapid assessment of molecular pathways controlling epithelial regeneration. For complete details on the use and execution of this profile, please refer to Wurster et al. (2021).

Protocol for fungal infection following the induction of epithelial cell loss in larval zebrafish.

Epithelia provide the first line of defense against foreign pathogens, and disruption of tissue homeostasis frequently allows for opportunistic infections. Here we provide a protocol for induction of epithelial cell loss in zebrafish larvae, followed by infection with fungal pathogens. Details are provided for monitoring larval survival after infection, assessment of fungal burden, and prophylactic treatment with antifungal compounds. Limitations of the protocol include potential antifungal toxicity and high fungal inoculums to induce lethal infection with some pathogenic fungal species. For complete details on the use and execution of this protocol, please refer to Wurster et al. (2021).

Protocol for quantitative analysis of pulsatile contractions and cell extrusion in epithelial tissues of larval zebrafish.

Cell elimination by extrusion is important for epithelial homeostasis, but knowing when and where cells will extrude has made in vivo studies difficult. Here, we describe a step-by-step protocol for inducing cell extrusion from the larval zebrafish epidermis. We detail how to capture the dynamics of extrusion via time-lapse imaging and describe how existing protocols can be implemented for the analysis of cell shape changes preceding extrusion events and derivation of mechanical measurements associated with these shape changes. For complete details on the use and execution of this protocol, please refer to Atieh et al. (2021).

EGF-mediated suppression of cell extrusion during mucosal damage attenuates opportunistic fungal invasion.

Severe and often fatal opportunistic fungal infections arise frequently following mucosal damage caused by trauma or cytotoxic chemotherapy. Interaction of fungal pathogens with epithelial cells that comprise mucosae is a key early event associated with invasion, and, therefore, enhancing epithelial defense mechanisms may mitigate infection. Here, we establish a model of mold and yeast infection mediated by inducible epithelial cell loss in larval zebrafish. Epithelial cell loss by extrusion promotes exposure of laminin associated with increased fungal attachment, invasion, and larval lethality, whereas fungi defective in adherence or filamentation have reduced virulence. Transcriptional profiling identifies significant upregulation of the epidermal growth factor receptor ligand epigen (EPGN) upon mucosal damage. Treatment with recombinant human EPGN suppresses epithelial cell extrusion, leading to reduced fungal invasion and significantly enhanced survival. These data support the concept of augmenting epithelial restorative capacity to attenuate pathogenic invasion of fungi associated with human disease.

FishNET: An automated relational database for zebrafish colony management.

The zebrafish Danio rerio is a powerful model system to study the genetics of development and disease. However, maintenance of zebrafish husbandry records is both time intensive and laborious, and a standardized way to manage and track the large amount of unique lines in a given laboratory or centralized facility has not been embraced by the field. Here, we present FishNET, an intuitive, open-source, relational database for managing data and information related to zebrafish husbandry and maintenance. By creating a "virtual facility," FishNET enables users to remotely inspect the rooms, racks, tanks, and lines within a given facility. Importantly, FishNET scales from one laboratory to an entire facility with several laboratories to multiple facilities, generating a cohesive laboratory and community-based platform. Automated data entry eliminates confusion regarding line nomenclature and streamlines maintenance of individual lines, while flexible query forms allow researchers to retrieve database records based on user-defined criteria. FishNET also links associated embryonic and adult biological samples with data, such as genotyping results or confocal images, to enable robust and efficient colony management and storage of laboratory information. A shared calendar function with email notifications and automated reminders for line turnover, automated tank counts, and census reports promote communication with both end users and administrators. The expected benefits of FishNET are improved vivaria efficiency, increased quality control for experimental numbers, and flexible data reporting and retrieval. FishNET's easy, intuitive record management and open-source, end-user-modifiable architecture provides an efficient solution to real-time zebrafish colony management for users throughout a facility and institution and, in some cases, across entire research hubs.

Stem cell proliferation is induced by apoptotic bodies from dying cells during epithelial tissue maintenance.

Epithelial tissues require the removal and replacement of damaged cells to sustain a functional barrier. Dying cells provide instructive cues that can influence surrounding cells to proliferate, but how these signals are transmitted to their healthy neighbors to control cellular behaviors during tissue homeostasis remains poorly understood. Here we show that dying stem cells facilitate communication with adjacent stem cells by caspase-dependent production of Wnt8a-containing apoptotic bodies to drive cellular turnover in living epithelia. Basal stem cells engulf apoptotic bodies, activate Wnt signaling, and are stimulated to divide to maintain tissue-wide cell numbers. Inhibition of either cell death or Wnt signaling eliminated the apoptosis-induced cell division, while overexpression of Wnt8a signaling combined with induced cell death led to an expansion of the stem cell population. We conclude that ingestion of apoptotic bodies represents a regulatory mechanism linking death and division to maintain overall stem cell numbers and epithelial tissue homeostasis.

Dynamic regulation of VEGF-inducible genes by an ERK/ERG/p300 transcriptional network.

The transcriptional pathways activated downstream of vascular endothelial growth factor (VEGF) signaling during angiogenesis remain incompletely characterized. By assessing the signals responsible for induction of the Notch ligand delta-like 4 (DLL4) in endothelial cells, we find that activation of the MAPK/ERK pathway mirrors the rapid and dynamic induction of DLL4 transcription and that this pathway is required for DLL4 expression. Furthermore, VEGF/ERK signaling induces phosphorylation and activation of the ETS transcription factor ERG, a prerequisite for DLL4 induction. Transcription of DLL4 coincides with dynamic ERG-dependent recruitment of the transcriptional co-activator p300. Genome-wide gene expression profiling identified a network of VEGF-responsive and ERG-dependent genes, and ERG chromatin immunoprecipitation (ChIP)-seq revealed the presence of conserved ERG-bound putative enhancer elements near these target genes. Functional experiments performed in vitro and in vivo confirm that this network of genes requires ERK, ERG and p300 activity. Finally, genome-editing and transgenic approaches demonstrate that a highly conserved ERG-bound enhancer located upstream of HLX (which encodes a transcription factor implicated in sprouting angiogenesis) is required for its VEGF-mediated induction. Collectively, these findings elucidate a novel transcriptional pathway contributing to VEGF-dependent angiogenesis.

A toolbox to study epidermal cell types in zebrafish.

Epithelia provide a crucial protective barrier for our organs and are also the sites where the majority of carcinomas form. Most studies on epithelia and carcinomas use cell culture or organisms where high-resolution live imaging is inaccessible without invasive techniques. Here, we introduce the developing zebrafish epidermis as an excellent in vivo model system for studying a living epithelium. We developed tools to fluorescently tag specific epithelial cell types and express genes in a mosaic fashion using five Gal4 lines identified from an enhancer trap screen. When crossed to a variety of UAS effector lines, we can now track, ablate or monitor single cells at sub-cellular resolution. Using photo-cleavable morpholino oligonucleotides that target gal4, we can also express genes in a mosaic fashion at specific times during development. Together, this system provides an excellent in vivo alternative to tissue culture cells, without the intrinsic concerns of culture conditions or transformation, and enables the investigation of distinct cell types within living epithelial tissues.

Optical Enhancement of Exoskeleton-Based Estimation of Glenohumeral Angles.

In Robot-Assisted Rehabilitation (RAR) the accurate estimation of the patient limb joint angles is critical for assessing therapy efficacy. In RAR, the use of classic motion capture systems (MOCAPs) (e.g., optical and electromagnetic) to estimate the Glenohumeral (GH) joint angles is hindered by the exoskeleton body, which causes occlusions and magnetic disturbances. Moreover, the exoskeleton posture does not accurately reflect limb posture, as their kinematic models differ. To address the said limitations in posture estimation, we propose installing the cameras of an optical marker-based MOCAP in the rehabilitation exoskeleton. Then, the GH joint angles are estimated by combining the estimated marker poses and exoskeleton Forward Kinematics. Such hybrid system prevents problems related to marker occlusions, reduced camera detection volume, and imprecise joint angle estimation due to the kinematic mismatch of the patient and exoskeleton models. This paper presents the formulation, simulation, and accuracy quantification of the proposed method with simulated human movements. In addition, a sensitivity analysis of the method accuracy to marker position estimation errors, due to system calibration errors and marker drifts, has been carried out. The results show that, even with significant errors in the marker position estimation, method accuracy is adequate for RAR.

Upper limb posture estimation in robotic and virtual reality-based rehabilitation.

New motor rehabilitation therapies include virtual reality (VR) and robotic technologies. In limb rehabilitation, limb posture is required to (1) provide a limb realistic representation in VR games and (2) assess the patient improvement. When exoskeleton devices are used in the therapy, the measurements of their joint angles cannot be directly used to represent the posture of the patient limb, since the human and exoskeleton kinematic models differ. In response to this shortcoming, we propose a method to estimate the posture of the human limb attached to the exoskeleton. We use the exoskeleton joint angles measurements and the constraints of the exoskeleton on the limb to estimate the human limb joints angles. This paper presents (a) the mathematical formulation and solution to the problem, (b) the implementation of the proposed solution on a commercial exoskeleton system for the upper limb rehabilitation, (c) its integration into a rehabilitation VR game platform, and (d) the quantitative assessment of the method during elbow and wrist analytic training. Results show that this method properly estimates the limb posture to (i) animate avatars that represent the patient in VR games and (ii) obtain kinematic data for the patient assessment during elbow and wrist analytic rehabilitation.

Drosophila Zpr1 (Zinc finger protein 1) is required downstream of both EGFR and FGFR signaling in tracheal subcellular lumen formation.

The cellular and molecular cues involved in creating branched tubular networks that transport liquids or gases throughout an organism are not well understood. To identify factors required in branching and lumen formation of Drosophila tracheal terminal cells, a model for branched tubular networks, we performed a forward genetic-mosaic screen to isolate mutations affecting these processes. From this screen, we have identified the first Drosophila mutation in the gene Zpr1 (Zinc finger protein 1) by the inability of Zpr1-mutant terminal cells to form functional, gas-filled lumens. We show that Zpr1 defective cells initiate lumen formation, but are blocked from completing the maturation required for gas filling. Zpr1 is an evolutionarily conserved protein first identified in mammalian cells as a factor that binds the intracellular domain of the unactivated epidermal growth factor receptor (EGFR). We show that down-regulation of EGFR in terminal cells phenocopies Zpr1 mutations and that Zpr1 is epistatic to ectopic lumen formation driven by EGFR overexpression. However, while Zpr1 mutants are fully penetrant, defects observed when reducing EGFR activity are only partially penetrant. These results suggest that a distinct pathway operating in parallel to the EGFR pathway contributes to lumen formation, and this pathway is also dependent on Zpr1. We provide evidence that this alternative pathway may involve fibroblast growth factor receptor (FGFR) signaling. We suggest a model in which Zpr1 mediates both EGFR and FGFR signal transduction cascades required for lumen formation in terminal cells. To our knowledge, this is the first genetic evidence placing Zpr1 downstream of EGFR signaling, and the first time Zpr1 has been implicated in FGFR signaling. Finally, we show that down-regulation of Smn, a protein known to interact with Zpr1 in mammalian cells, shows defects similar to Zpr1 mutants.

Mutations in 2 distinct genetic pathways result in cerebral cavernous malformations in mice.

Cerebral cavernous malformations (CCMs) are a common type of vascular malformation in the brain that are a major cause of hemorrhagic stroke. This condition has been independently linked to 3 separate genes: Krev1 interaction trapped (KRIT1), Cerebral cavernous malformation 2 (CCM2), and Programmed cell death 10 (PDCD10). Despite the commonality in disease pathology caused by mutations in these 3 genes, we found that the loss of Pdcd10 results in significantly different developmental, cell biological, and signaling phenotypes from those seen in the absence of Ccm2 and Krit1. PDCD10 bound to germinal center kinase III (GCKIII) family members, a subset of serine-threonine kinases, and facilitated lumen formation by endothelial cells both in vivo and in vitro. These findings suggest that CCM may be a common tissue manifestation of distinct mechanistic pathways. Nevertheless, loss of heterozygosity (LOH) for either Pdcd10 or Ccm2 resulted in CCMs in mice. The murine phenotype induced by loss of either protein reproduced all of the key clinical features observed in human patients with CCM, as determined by direct comparison with genotype-specific human surgical specimens. These results suggest that CCM may be more effectively treated by directing therapies based on the underlying genetic mutation rather than treating the condition as a single clinical entity.