Stem cell-based models of embryos: The need for improved naming conventions

Stem cell-based models of embryos are known by various names, with different naming conventions, leading to confusion regarding their composition and potential. We propose the need for a general term for the field to promote public engagement and the development of a systematic nomenclature system to differentiate between specific models.

Rethinking Human Embryo Research Policies

It now seems technically feasible to culture human embryos beyond the "fourteen-day limit," which has the potential to increase scientific understanding of human development and perhaps improve infertility treatments. The fourteen-day limit was adopted as a compromise but subsequently has been considered an ethical line. Does it remain relevant in light of technological advances permitting embryo maturation beyond it? Should it be changed and, if so, how and why? What justifications would be necessary to expand the limit, particularly given that doing so would violate some people's moral commitments regarding human embryos? Robust stakeholder engagement preceded adoption of the fourteen-day limit and should arguably be part of efforts to reassess it. Such engagement could also consider the need for enhanced oversight of human embryo research. In the meantime, developing and implementing reliable oversight systems should help foster high-quality research and public confidence in it.

AIBP-mediated cholesterol efflux instructs hematopoietic stem and progenitor cell fate

Hypercholesterolemia, the driving force of atherosclerosis, accelerates the expansion and mobilization of hematopoietic stem and progenitor cells (HSPCs). The molecular determinants connecting hypercholesterolemia with hematopoiesis are unclear. Here, we report that a somite-derived prohematopoietic cue, AIBP, orchestrates HSPC emergence from the hemogenic endothelium, a type of specialized endothelium manifesting hematopoietic potential. Mechanistically, AIBP-mediated cholesterol efflux activates endothelial Srebp2, the master transcription factor for cholesterol biosynthesis, which in turn transactivates Notch and promotes HSPC emergence. Srebp2 inhibition impairs hypercholesterolemia-induced HSPC expansion. Srebp2 activation and Notch up-regulation are associated with HSPC expansion in hypercholesterolemic human subjects. Genome-wide chromatin immunoprecipitation followed by sequencing (ChIP-seq), RNA sequencing (RNA-seq), and assay for transposase-accessible chromatin using sequencing (ATAC-seq) indicate that Srebp2 transregulates Notch pathway genes required for hematopoiesis. Our studies outline an AIBP-regulated Srebp2-dependent paradigm for HSPC emergence in development and HPSC expansion in atherosclerotic cardiovascular disease.

Tuning the dynamic range of bacterial promoters regulated by ligand-inducible transcription factors

One challenge for synthetic biologists is the predictable tuning of genetic circuit regulatory components to elicit desired outputs. Gene expression driven by ligand-inducible transcription factor systems must exhibit the correct ON and OFF characteristics: appropriate activation and leakiness in the presence and absence of inducer, respectively. However, the dynamic range of a promoter (i.e., absolute difference between ON and OFF states) is difficult to control. We report a method that tunes the dynamic range of ligand-inducible promoters to achieve desired ON and OFF characteristics. We build combinatorial sets of AraC-and LasR-regulated promoters containing -10 and -35 sites from synthetic and Escherichia coli promoters. Four sequence combinations with diverse dynamic ranges were chosen to build multi-input transcriptional logic gates regulated by two and three ligand-inducible transcription factors (LacI, TetR, AraC, XylS, RhlR, LasR, and LuxR). This work enables predictable control over the dynamic range of regulatory components.

Role of WNT10A in failure of tooth development in humans and zebrafish

BACKGROUND

Oligodontia is a severe form of tooth agenesis characterized by the absence of six or more permanent teeth. Oligodontia has complex etiology and variations in numerous genes have been suggested as causal for the condition.

METHODS

We applied whole-exome sequencing (WES) to identify the cause of oligodontia in a 9-year-old girl missing 11 permanent teeth. Protein modeling and functional analysis in zebrafish were also performed to understand the impact of identified variants on the phenotype.

RESULTS

We identified a novel compound heterozygous missense mutation in WNT10A (c.637G>A:p.Gly213Ser and c.1070C>T:p.Thr357Ile) as the likely cause of autosomal recessive oligodontia in the child. Affected residues are located in conserved regions and variants are predicted to be highly deleterious for potentially destabilizing the protein fold and inhibiting normal protein function. Functional studies in zebrafish embryos showed that wnt10a is expressed in the craniofacies at critical time points for tooth development, and that perturbations of wnt10a expression impaired normal tooth development and arrested tooth development at 5 days postfertilization (dpf). Furthermore, mRNA expression levels of additional tooth development genes were directly correlated with wnt10a expression; expression of msx1, dlx2b, eda, and axin2 was decreased upon wnt10a knockdown, and increased upon wnt10a overexpression.

CONCLUSIONS

Our results reveal a novel compound heterozygous variant in WNT10A as pathogenic for oligodontia, and demonstrate that perturbations of wnt10a expression in zebrafish may directly and/or indirectly affect tooth development recapitulating the agenesis phenotype observed in humans.

RICE CRISPR: Rapidly increased cut ends by an exonuclease Cas9 fusion in zebrafish

Application of CRISPR-Cas9 technology in diverse organisms has resulted in an explosion of genome modification efforts. To expand the toolbox of applications, we have created an E. coli Exonuclease I (sbcB)-Cas9 fusion that has altered enzymatic activity in zebrafish embryos. This Cas9 variant has increased mutation efficiency and favors longer deletions relative to wild-type Cas9. We anticipate that this variant will allow for more efficient screening for F0 phenotypes and mutation of a larger spectrum of genomic targets including deletion of regulatory regions and creating loss of function mutations in transcription units with poor sequence conservation such as lncRNAs where larger deletions may be required for loss of function.

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.

Endothelial cells decode VEGF-mediated Ca2+ signaling patterns to produce distinct functional responses

A single extracellular stimulus can promote diverse behaviors among isogenic cells by differentially regulated signaling networks. We examined Ca(2+) signaling in response to VEGF (vascular endothelial growth factor), a growth factor that can stimulate different behaviors in endothelial cells. We found that altering the amount of VEGF signaling in endothelial cells by stimulating them with different VEGF concentrations triggered distinct and mutually exclusive dynamic Ca(2+) signaling responses that correlated with different cellular behaviors. These behaviors were cell proliferation involving the transcription factor NFAT (nuclear factor of activated T cells) and cell migration involving MLCK (myosin light chain kinase). Further analysis suggested that this signal decoding was robust to the noisy nature of the signal input. Using probabilistic modeling, we captured both the stochastic and deterministic aspects of Ca(2+) signal decoding and accurately predicted cell responses in VEGF gradients, which we used to simulate different amounts of VEGF signaling. Ca(2+) signaling patterns associated with proliferation and migration were detected during angiogenesis in developing zebrafish.

Neuropilin 1 balances β8 integrin-activated TGFβ signaling to control sprouting angiogenesis in the brain

Angiogenesis in the developing central nervous system (CNS) is regulated by neuroepithelial cells, although the genes and pathways that couple these cells to blood vessels remain largely uncharacterized. Here, we have used biochemical, cell biological and molecular genetic approaches to demonstrate that β8 integrin (Itgb8) and neuropilin 1 (Nrp1) cooperatively promote CNS angiogenesis by mediating adhesion and signaling events between neuroepithelial cells and vascular endothelial cells. β8 integrin in the neuroepithelium promotes the activation of extracellular matrix (ECM)-bound latent transforming growth factor β (TGFβ) ligands and stimulates TGFβ receptor signaling in endothelial cells. Nrp1 in endothelial cells suppresses TGFβ activation and signaling by forming intercellular protein complexes with β8 integrin. Cell type-specific ablation of β8 integrin, Nrp1, or canonical TGFβ receptors results in pathological angiogenesis caused by defective neuroepithelial cell-endothelial cell adhesion and imbalances in canonical TGFβ signaling. Collectively, these data identify a paracrine signaling pathway that links the neuroepithelium to blood vessels and precisely balances TGFβ signaling during cerebral angiogenesis.

Summary: Neuropilin 1 and β8 integrin cooperatively promote cerebral angiogenesis by mediating adhesion and signaling events between neuroepithelial cells and vascular endothelial cells in the mouse brain.

Crispld2 is required for neural crest cell migration and cell viability during zebrafish craniofacial development

The CAP superfamily member, CRISPLD2, has previously been shown to be associated with nonsyndromic cleft lip and palate (NSCLP) in human populations and to be essential for normal craniofacial development in the zebrafish. Additionally, in rodent models, CRISPLD2 has been shown to play a role in normal lung and kidney development. However, the specific role of CRISPLD2 during these developmental processes has yet to be determined. In this study, it was demonstrated that Crispld2 protein localizes to the orofacial region of the zebrafish embryo and knockdown of crispld2 resulted in abnormal migration of neural crest cells (NCCs) during both early and late time points. An increase in cell death after crispld2 knockdown as well as an increase in apoptotic marker genes was also shown. This data suggests that Crispld2 modulates the migration, differentiation, and/or survival of NCCs during early craniofacial development. These results indicate an important role for Crispld2 in NCC migration during craniofacial development and suggests involvement of Crispld2 in cell viability during formation of the orofacies.

The impact of cerebral embolization during infant cardiac surgery on neurodevelopmental outcomes at intermediate follow-up

Cerebral embolization during pediatric cardiac surgery may be an underappreciated source of subsequent neurodevelopmental impairment. Transcranial Doppler ultrasound is a neuromonitoring tool that can provide intraoperative surveillance for cerebral embolization. We hypothesized that increased cerebral embolic signals detected during infant cardiac surgery would be associated with worse neurodevelopmental outcomes at follow-up. A study group of 24 children who underwent infant cardiac surgery with transcranial Doppler detection of cerebral embolic signals returned at intermediate follow-up for standardized neurodevelopmental assessment. The children were evaluated using two neurocognitive tests and the parents completed two questionnaires regarding observed behavior. Statistical analysis assessed for correlation between the number of cerebral embolic signals at surgery and the results of the neurodevelopmental assessment. Of the 67 test parameters analyzed, five showed a significant association with the number of embolic signals, yet, all in the contrary direction of the clinical hypothesis, likely representing a Type I error. Thus, in this small cohort of patients, the number of cerebral embolic signals detected during infant cardiac surgery was not shown to be associated with worse neurodevelopmental outcomes at intermediate follow-up. A larger study is probably necessary to ascertain the potential influence of cerebral embolic signals on eventual neurologic outcomes in children. The clinical relevance of cerebral embolic signals during pediatric cardiac surgery remains undetermined and deserves further investigation.

Biochar and microbial signaling: production conditions determine effects on microbial communication

Charcoal has a long soil residence time, which has resulted in its production and use as a carbon sequestration technique (biochar). A range of biological effects can be triggered by soil biochar that can positively and negatively influence carbon storage, such as changing the decomposition rate of organic matter and altering plant biomass production. Sorption of cellular signals has been hypothesized to underlie some of these effects, but it remains unknown whether the binding of biochemical signals occurs, and if so, on time scales relevant to microbial growth and communication. We examined biochar sorption of N-3-oxo-dodecanoyl-L-homoserine lactone, an acyl-homoserine lactone (AHL) intercellular signaling molecule used by many gram-negative soil microbes to regulate gene expression. We show that wood biochars disrupt communication within a growing multicellular system that is made up of sender cells that synthesize AHL and receiver cells that express green fluorescent protein in response to an AHL signal. However, biochar inhibition of AHL-mediated cell-cell communication varied, with the biochar prepared at 700 °C (surface area of 301 m(2)/g) inhibiting cellular communication 10-fold more than an equivalent mass of biochar prepared at 300 °C (surface area of 3 m(2)/g). These findings provide the first direct evidence that biochars elicit a range of effects on gene expression dependent on intercellular signaling, implicating the method of biochar preparation as a parameter that could be tuned to regulate microbial-dependent soil processes, like nitrogen fixation and pest attack of root crops.

Interferon regulatory factor 6 promotes differentiation of the periderm by activating expression of Grainyhead-like 3

Interferon Regulatory Factor 6 (IRF6) is a transcription factor that, in mammals, is required for the differentiation of skin, breast epithelium, and oral epithelium. However, the transcriptional targets that mediate these effects are currently unknown. In zebrafish and frog embryos Irf6 is necessary for differentiation of the embryonic superficial epithelium, or periderm. Here we use microarrays to identify genes that are expressed in the zebrafish periderm and whose expression is inhibited by a dominant-negative variant of Irf6 (dnIrf6). These methods identify Grhl3, an ancient regulator of the epidermal permeability barrier, as acting downstream of Irf6. In human keratinocytes, IRF6 binds conserved elements near the GHRL3 promoter. We show that one of these elements has enhancer activity in human keratinocytes and zebrafish periderm, suggesting that Irf6 directly stimulates Grhl3 expression in these tissues. Simultaneous inhibition of grhl1 and grhl3 disrupts periderm differentiation in zebrafish, and, intriguingly, forced grhl3 expression restores periderm markers in both zebrafish injected with dnIrf6 and frog embryos depleted of Irf6. Finally, in Irf6 deficient mouse embryos, Grhl3 expression in the periderm and oral epithelium is virtually absent. These results indicate that Grhl3 is a key effector of Irf6 in periderm differentiation.

Cell-specific transmembrane injection of molecular cargo with gold nanoparticle-generated transient plasmonic nanobubbles

Optimal cell therapies require efficient, selective and rapid delivery of molecular cargo into target cells without compromising their viability. Achieving these goals ex vivo in bulk heterogeneous multi-cell systems such as human grafts is impeded by low selectivity and speed of cargo delivery and by significant damage to target and non-target cells. We have developed a cell level approach for selective and guided transmembrane injection of extracellular cargo into specific target cells using transient plasmonic nanobubbles (PNB) as cell-specific nano-injectors. As a technical platform for this method we developed a laser flow cell processing system. The PNB injection method and flow system were tested in heterogeneous cell suspensions of target and non-target cells for delivery of Dextran-FITC dye into squamous cell carcinoma HN31 cells and transfection of human T-cells with a green fluorescent protein-encoding plasmid. In both models the method demonstrated single cell type selectivity, high efficacy of delivery (96% both for HN31 cells T-cells), speed of delivery (nanoseconds) and viability of treated target cells (96% for HN31 cells and 75% for T-cells). The PNB injection method may therefore be beneficial for real time processing of human grafts without removal of physiologically important cells.

Pronephric tubulogenesis requires Daam1-mediated planar cell polarity signaling

Canonical β-catenin-mediated Wnt signaling is essential for the induction of nephron development. Noncanonical Wnt/planar cell polarity (PCP) pathways contribute to processes such as cell polarization and cytoskeletal modulation in several tissues. Although PCP components likely establish the plane of polarization in kidney tubulogenesis, whether PCP effectors directly modulate the actin cytoskeleton in tubulogenesis is unknown. Here, we investigated the roles of Wnt PCP components in cytoskeletal assembly during kidney tubule morphogenesis in Xenopus laevis and zebrafish. We found that during tubulogenesis, the developing pronephric anlagen expresses Daam1 and its interacting Rho-GEF (WGEF), which compose one PCP/noncanonical Wnt pathway branch. Knockdown of Daam1 resulted in reduced expression of late pronephric epithelial markers with no apparent effect upon early markers of patterning and determination. Inhibiting various points in the Daam1 signaling pathway significantly reduced pronephric tubulogenesis. These data indicate that pronephric tubulogenesis requires the Daam1/WGEF/Rho PCP pathway.

Mutations in zebrafish lrp2 result in adult-onset ocular pathogenesis that models myopia and other risk factors for glaucoma

The glaucomas comprise a genetically complex group of retinal neuropathies that typically occur late in life and are characterized by progressive pathology of the optic nerve head and degeneration of retinal ganglion cells. In addition to age and family history, other significant risk factors for glaucoma include elevated intraocular pressure (IOP) and myopia. The complexity of glaucoma has made it difficult to model in animals, but also challenging to identify responsible genes. We have used zebrafish to identify a genetically complex, recessive mutant that shows risk factors for glaucoma including adult onset severe myopia, elevated IOP, and progressive retinal ganglion cell pathology. Positional cloning and analysis of a non-complementing allele indicated that non-sense mutations in low density lipoprotein receptor-related protein 2 (lrp2) underlie the mutant phenotype. Lrp2, previously named Megalin, functions as an endocytic receptor for a wide-variety of bioactive molecules including Sonic hedgehog, Bone morphogenic protein 4, retinol-binding protein, vitamin D-binding protein, and apolipoprotein E, among others. Detailed phenotype analyses indicated that as lrp2 mutant fish age, many individuals—but not all—develop high IOP and severe myopia with obviously enlarged eye globes. This results in retinal stretch and prolonged stress to retinal ganglion cells, which ultimately show signs of pathogenesis. Our studies implicate altered Lrp2-mediated homeostasis as important for myopia and other risk factors for glaucoma in humans and establish a new genetic model for further study of phenotypes associated with this disease.

Complex genetic inheritance, including variable penetrance and severity, underlies many common eye diseases. In this study, we present analysis of a zebrafish mutant, bugeye, which shows complex inheritance of multiple ocular phenotypes that are known risk factors for glaucoma, including high myopia, elevated intraocular pressure, and up-regulation of stress-response genes in retinal ganglion cells. Molecular genetic analysis revealed that mutations in low density lipoprotein receptor-related protein 2 (lrp2) underlie the mutant phenotypes. Lrp2 is a large transmembrane protein expressed in epithelia of the eye. It facilitates transport and clearance of multiple secreted bioactive factors through receptor-mediated endocytosis. Glaucoma, a progressive blinding disorder, usually presents in adulthood and is characterized by optic nerve damage followed by ganglion cell death. In bugeye/lrp2 mutants, ganglion cell death was significantly elevated, but surprisingly moderate, and therefore they do not model this endpoint of glaucoma. As such, bugeye/lrp2 mutants should be considered valuable as a genetic model (A) for buphthalmia, myopia, and regulated eye growth; (B) for identifying genes and pathways that modify the observed ocular phenotypes; and (C) for studying the initiation of retinal ganglion cell pathology in the context of high myopia and elevated intraocular pressure.

Tunable plasmonic nanoprobes for theranostics of prostate cancer

Theranostic applications require coupling of diagnosis and therapy, a high degree of specificity and adaptability to delivery methods compatible with clinical practice. The tunable physical and biological effects of selective targeting and activation of plasmonic nanobubbles (PNB) were studied in a heterogeneous biological microenvironment of prostate cancer and stromal cells. All cells were targeted with conjugates of gold nanoparticles (NPs) through an antibody-receptor-endocytosis-nanocluster mechanism that produced NP clusters. The simultaneous pulsed optical activation of intracellular NP clusters at several wavelengths resulted in higher optical contrast and therapeutic selectivity of PNBs compared with those of gold NPs alone. The developed mechanism was termed "rainbow plasmonic nanobubbles." The cellular effect of rainbow PNBs was tuned in situ in target cells, thus supporting a theranostic algorithm of prostate cancer cell detection and follow-up guided destruction without damage to collateral cells. The specificity and tunability of PNBs is promising for theranostic applications and we discuss a fiber optic platform that will capitalize on these features to bring theranostic tools to the clinic.

poky/chuk/ikk1 is required for differentiation of the zebrafish embryonic epidermis

An epidermis surrounds all vertebrates, forming a water barrier between the external environment and the internal space of the organism. In the zebrafish, the embryonic epidermis consists of an outer enveloping layer (EVL) and an inner basal layer that have distinct embryonic origins. Differentiation of the EVL requires the maternal effect gene poky/ikk1 in EVL cells prior to establishment of the basal layer. This requirement is transient and maternal Ikk1 is sufficient to allow establishment of the EVL and formation of normal skin in adults. Similar to the requirement for Ikk1 in mouse epidermis, EVL cells in poky mutants fail to exit the cell cycle or express specific markers of differentiation. In spite of the similarity in phenotype, the molecular requirement for Ikk1 is different between mouse and zebrafish. Unlike the mouse, EVL differentiation requires functioning Poky/Ikk1 kinase activity but does not require the HLH domain. Previous work suggested that the EVL was a transient embryonic structure, and that maturation of the epidermis required replacement of the EVL with cells from the basal layer. We show here that the EVL is not lost during embryogenesis but persists to larval stages. Our results show that while the requirement for poky/ikk1 is conserved, the differences in molecular activity indicate that diversification of an epithelial differentiation program has allowed at least two developmental modes of establishing a multilayered epidermis in vertebrates.

The in vivo performance of plasmonic nanobubbles as cell theranostic agents in zebrafish hosting prostate cancer xenografts

Cell theranostics is a new approach that unites diagnosis, therapy and confirmation (guidance) of the results of therapy in one single process at cell level, thus principally improving both the rapidity and precision of treatment. The ideal theranostic agent will support all three of the above functions in vivo with cellular resolution, allowing individual assessment of disease state and the elimination of diseased cells while leaving healthy cells intact. We have developed and evaluated plasmonic nanobubbles (PNBs) as an in vivo tunable theranostic cellular agent in zebrafish hosting prostate cancer xenografts. PNBs were selectively generated around gold nanoparticles in cancer cells in the zebrafish with short single laser pulses. By varying the energy of the laser pulse, we dynamically tuned the PNB size in a theranostic sequence of two PNBs: an initial small PNB detected a cancer cell through optical scattering, followed by a second bigger PNB, which mechanically ablated this cell without damage to surrounding tissue, while its optical scattering confirmed the destruction of the cell. Thus PNBs supported the diagnosis and guided ablation of individual human cancer cells in a living organism without damage to the host.

Generation and detection of plasmonic nanobubbles in zebrafish

The zebrafish embryo has been evaluated as an in vivo model for plasmonic nanobubble (PNB) generation and detection at nanoscale. The embryo is easily observed and manipulated utilizing the same methodology as for application of PNBs in vitro. Injection and irradiation of gold nanoparticles with a short laser pulse resulted in generation of PNBs in zebrafish with similar parameters as for PNBs generated in water and cultured living cells. These PNBs do not result in systemic damage, thus we demonstrated an in vivo model for rapid and precise testing of plasmonic nanotechnologies.

Sequence and expression of the zebrafish alpha-actinin gene family reveals conservation and diversification among vertebrates

Alpha-actinins are actin microfilament crosslinking proteins. Vertebrate actinins fall into two classes: the broadly-expressed actinins 1 and 4 (actn1 and actn4) and muscle-specific actinins, actn2 and actn3. Members of this family have numerous roles, including regulation of cell adhesion, cell differentiation, directed cell motility, intracellular signaling, and stabilization of f-actin at the sarcomeric Z-line in muscle. Here we identify five zebrafish actinin genes including two paralogs of ACTN3. We describe the temporal and spatial expression patterns of these genes through embryonic development. All zebrafish actinin genes have unique expression profiles, indicating specialization of each gene. In particular, the muscle actinins display preferential expression in different domains of axial, pharyngeal, and cranial musculature. There is no identified avian actn3 and approximately 16% of humans are null for ACTN3. Duplication of actn3 in the zebrafish indicates that variation in actn3 expression may promote physiological diversity in muscle function among vertebrates.

Potency and sterility of anesthetic drugs in obstetric anesthesia

In order to estimate how long a medication can remain prepared before the integrity or concentration of the drug is compromised, we assessed the sterility and potency of medications commonly used in our obstetric anesthesia practice. Our goal was to evaluate the following drugs over a 30-day period: epinephrine, atropine, lidocaine, succinylcholine, and ephedrine. The medications were prepared by various medical staff, drawn into sterile plastic syringes and left at room temperature unprotected from light for the duration of the study. The syringes were collected daily, stored and randomly sampled after 7, 14, 21 and 30 days by research personnel. Potency and sterility of atropine, ephedrine and lidocaine were maintained over the study period. Succinylcholine and epinephrine could not be assayed but the solutions remained sterile for 30 and 14 days respectively. Data were incomplete for epinephrine. These findings suggest that some drugs that are commonly used in obstetric anesthesia are stable for long periods of time. Modification of current standards of practice could result in a significant reduction in drug waste and therefore cost.

Genetic screens for genes controlling motor nerve-muscle development and interactions

Motor growth cones navigate long and complex trajectories to connect with their muscle targets. Experimental studies have shown that this guidance process critically depends on extrinsic cues. In the zebrafish embryo, a subset of mesodermal cells, the adaxial cells, delineates the prospective path of pioneering motor growth cones. Genetic ablation of adaxial cells causes profound pathfinding defects, suggesting the existence of adaxial cell derived guidance factors. Intriguingly, adaxial cells are themselves migratory, and as growth cones approach they migrate away from the prospective axonal path to the lateral surface of the myotome, where they develop into slow-twitching muscle fibers. Genetic screens in embryos stained with an antibody cocktail identified mutants with specific defects in differentiation and migration of adaxial cells/slow muscle fibers, as well as mutants with specific defects in axonal pathfinding, including exit from the spinal cord and pathway selection. Together, the genes underlying these mutant phenotypes define pathways essential for nerve and muscle development and interactions between these two cell types.

Tumor-infiltrating dendritic cell precursors recruited by a beta-defensin contribute to vasculogenesis under the influence of Vegf-A

The involvement of immune mechanisms in tumor angiogenesis is unclear. Here we describe a new mechanism of tumor vasculogenesis mediated by dendritic cell (DC) precursors through the cooperation of beta-defensins and vascular endothelial growth factor-A (Vegf-A). Expression of mouse beta-defensin-29 recruited DC precursors to tumors and enhanced tumor vascularization and growth in the presence of increased Vegf-A expression. A new leukocyte population expressing DC and endothelial markers was uncovered in mouse and human ovarian carcinomas coexpressing Vegf-A and beta-defensins. Tumor-infiltrating DCs migrated to tumor vessels and independently assembled neovasculature in vivo. Bone marrow-derived DCs underwent endothelial-like differentiation ex vivo, migrated to blood vessels and promoted the growth of tumors expressing high levels of Vegf-A. We show that beta-defensins and Vegf-A cooperate to promote tumor vasculogenesis by carrying out distinct tasks: beta-defensins chemoattract DC precursors through CCR6, whereas Vegf-A primarily induces their endothelial-like specialization and migration to vessels, which is mediated by Vegf receptor-2.

Maternal control of vertebrate development before the midblastula transition: mutants from the zebrafish I

Maternal factors control development prior to the activation of the embryonic genome. In vertebrates, little is known about the molecular mechanisms by which maternal factors regulate embryonic development. To understand the processes controlled by maternal factors and identify key genes involved, we embarked on a maternal-effect mutant screen in the zebrafish. We identified 68 maternal-effect mutants. Here we describe 15 mutations in genes controlling processes prior to the midblastula transition, including egg development, blastodisc formation, embryonic polarity, initiation of cell cleavage, and cell division. These mutants exhibit phenotypes not previously observed in zygotic mutant screens. This collection of maternal-effect mutants provides the basis for a molecular genetic analysis of the maternal control of embryogenesis in vertebrates.

Maternal Control of Development at the Midblastula Transition and beyond

Many maternal factors in the oocyte persist in the embryo. They are required to initiate zygotic transcription but also function beyond this stage, where they interact with zygotic gene products during embryonic development. In a four-generation screen in the zebrafish, we identified 47 maternal-effect and five paternal-effect mutants that manifest their phenotypes at the time of, or after, zygotic genome activation. We propagated a subset of 13 mutations that cause developmental arrest at the midblastula transition, defects in cell viability, embryonic morphogenesis, and establishment of the embryonic body plan. This diverse group of mutants, many not previously observed in vertebrates, demonstrates a substantial maternal contribution to the "zygotic" period of embryogenesis and a surprising degree of paternal control. These mutants provide powerful tools to dissect the maternal and paternal control of vertebrate embryogenesis.

Maternally supplied Smad5 is required for ventral specification in zebrafish embryos prior to zygotic Bmp signaling

We have previously shown that the maternal effect dorsalization of zebrafish embryos from sbn(dtc24) heterozygous mothers is caused by a dominant negative mutation in Smad5, a transducer of ventralizing signaling by the bone morphogenetic proteins Bmp2b and Bmp7. Since sbn(dtc24) mutant Smad5 protein not only blocks wild-type Smad5, but also other family members like Smad1, it remained open to what extent Smad5 itself is required for dorsoventral patterning. Here, we report the identification of novelsmad5 alleles: three new isolates coming from a dominant enhancer screen, and four former isolates initially assigned to the cpt and pgy complementation groups. Overexpression analyses demonstrate that three of the new alleles, m169, fr5, and tc227, are true nulls (amorphs), whereas the initial dtc24 allele is both antimorphic and hypomorphic. We rescued m169 mutant embryos by smad5 mRNA injection. Although adult mutants are smaller than their siblings, the eggs laid by m169(-/-) females are larger than normal eggs. Embryos lacking maternal Smad5 function (Mm169(-/-) embryos) are even more strongly dorsalized thanbmp2b or bmp7 null mutants. They do not respond to injected bmp2b mRNA, indicating that Smad5 is absolutely essential for ventral development and Bmp2/7 signaling. Most importantly, Mm169(-/-) embryos display reducedbmp7 mRNA levels during blastula stages, when bmp2b and bmp7 mutants are still normal. This indicates that maternally supplied Smad5 is already required to mediate ventral specification prior to zygotic Bmp2/7 signaling to establish the initial dorsoventral asymmetry.

Modulation of BMP activity in dorsal-ventral pattern formation by the chordin and ogon antagonists

We analyzed the interactions between mutations in antagonistic BMP pathway signaling components to examine the roles that the antagonists play in regulating BMP signaling activity. The dorsalized mutants swirl/bmp2b, snailhouse/bmp7, lost-a-fin/alk8, and mini fin/tolloid were each analyzed in double mutant combinations with the ventralized mutants chordino/chordin and ogon, whose molecular nature is not known. Similar to the BMP antagonist chordino, we found that the BMP ligand mutants swirl/bmp2b and snailhouse/bmp7 are also epistatic to the putative BMP pathway antagonist, ogon, excluding a class of intracellular antagonists as candidates for ogon. In ogon;mini fin double mutants, we observed a mutual suppression of the ogon and mini fin mutant phenotypes, frequently to a wild type phenotype. Thus, the Tolloid/Mini fin metalloprotease that normally cleaves and inhibits Chordin activity is dispensable, when Ogon antagonism is reduced. These results suggest that Ogon encodes a Tolloid and Chordin-independent antagonistic function. By analyzing genes whose expression is very sensitive to BMP signaling levels, we found that the absence of Ogon or Chordin antagonism did not increase the BMP activity remaining in swirl/bmp2b or hypomorphic snailhouse/bmp7 mutants. These results, together with other studies, suggest that additional molecules or mechanisms are essential in generating the presumptive gastrula BMP activity gradient that patterns the dorsal-ventral axis. Lastly we observed a striking increased penetrance of the swirl/bmp2b dominant dorsalized phenotype, when Chordin function is also absent. Loss of the BMP antagonist Chordin is expected to increase BMP signaling levels in a swirl heterozygote, but instead we observed an apparent decrease in BMP signaling levels and a loss of ventral tail tissue. As has been proposed for the fly orthologue of chordin, short gastrulation, our paradoxical results can be explained by a model whereby Chordin both antagonizes and promotes BMP activity.

Genetic analysis of digestive physiology using fluorescent phospholipid reporters

Zebrafish are a valuable model for mammalian lipid metabolism; larvae process lipids similarly through the intestine and hepatobiliary system and respond to drugs that block cholesterol synthesis in humans. After ingestion of fluorescently quenched phospholipids, endogenous lipase activity and rapid transport of cleavage products results in intense gall bladder fluorescence. Genetic screening identifies zebrafish mutants, such as fat free, that show normal digestive organ morphology but severely reduced phospholipid and cholesterol processing. Thus, fluorescent lipids provide a sensitive readout of lipid metabolism and are a powerful tool for identifying genes that mediate vertebrate digestive physiology.

An outcomes analysis and satisfaction survey of 199 consecutive abdominoplasties

Abdominoplasty is a popular body-contouring procedure. In this study the authors review retrospectively 199 abdominoplasty patients during a 15-year period to identify factors that affect overall outcome. Patients included 190 women and 9 men. The complication rate was 32% with few major complications (1.4%). The revision rate was 43%, and was related to fine-tuning the aesthetic appearance. Patients were divided into four groups based on tobacco use and history of diabetes and hypertension. There was no significant difference in revision rates or major complications between the subgroups. Minor complication rates, however, were significantly higher in smokers and patients with diabetes and/or hypertension. Complication and revision rates in patients undergoing intra-abdominal procedures combined with abdominoplasty were not significantly different from those patients undergoing abdominoplasty alone. A patient survey revealed symptom improvement in 95% of patients. Eighty-six percent of patients were satisfied with their result, and 86% would recommend abdominoplasty to a friend. The authors conclude that abdominoplasty is a safe and satisfying procedure, whether performed alone or in conjunction with another procedure. Patients are pleased with the outcome and have improvement in their symptoms, with minimal health risk. There is, however, a significant incidence of minor complications, related primarily to wound healing. These complications are increased significantly in smokers and patients with diabetes and/or hypertension. Revision rates are not different significantly between the subgroups. When complications do occur or revisions are required, they are minor and managed easily in an office setting.

Effect of intravenous versus epidural fentanyl on the minimum local analgesic concentration of epidural bupivacaine in labor

BACKGROUND

The minimum local analgesic concentration (MLAC) has been defined as the median effective local analgesic concentration (EC50) in a 20-ml volume for epidural analgesia in the first stage of labor. The aim of this study was to determine the relative local anesthetic sparing efficacies of intravenous and epidural fentanyl by comparison of their effects on the MLAC of bupivacaine.

METHODS

In this double-blind, randomized, prospective study, 84 parturients at < or = 7-cm cervical dilation who requested epidural analgesia were allocated to one of two groups. After lumbar epidural catheter placement, 20 ml bupivacaine (n = 44) or bupivacaine with 3 microg/ml (60 microg) fentanyl (n = 40) was administered. The plain bupivacaine group then received 60 microg intravenous fentanyl. The bupivacaine-fentanyl group received intravenous saline. The concentration of bupivacaine was determined by the response of the previous patient in that group to a higher or lower concentration using up-down sequential allocation. Analgesic efficacy was assessed using 100-mm visual analog pain scores, with < or = 10 mm within 30 min define as effective.

RESULTS

The MLAC of bupivacaine-intravenous fentanyl was 0.064% wt/vol (95% confidence interval, 0.049-0.080), and the MLAC of bupivacaine-epidural fentanyl was 0.034% wt/vol (95% confidence interval, 0.017-0.050). Epidural fentanyl significantly increased the analgesic potency of bupivacaine by a factor of 1.88 (95% confidence interval, 1.09-3.67) compared with intravenous fentanyl. The epidural fentanyl group demonstrated significantly higher dermatomal spread (P = 0.0064) and increased pruritus (P = 0. 01).

CONCLUSIONS

Epidural fentanyl significantly reduced the MLAC of bupivacaine when compared with intravenous fentanyl for the parturients in this study. The significantly enhanced local anesthetic sparing, dermatomal level, and pruritus with epidural fentanyl suggest a primarily spinal site of action.

Identification of a differentially expressed RNA helicase by gene trapping

A mouse line was generated that expressed a gene trap reporter construct, betageo, in a dynamic pattern during embryonic development. Differential expression was seen within the developing eyes, limbs, heart, neural tube, and skeleton. Two transcripts were cloned that contained endogenous sequences fused to the gene trap vector sequence. Analysis of the endogenous sequences revealed that the reporter integrated within a gene belonging to a small group of eukaryotic superfamily I helicases. Unexpectedly, the majority of transcripts produced from the trapped locus were not affected by the insertion of the reporter. Although the function of the trapped helicase gene is unknown, its complex transcription patterns and widespread spatial-temporal distribution suggest that the gene product plays a role in RNA metabolism in multiple tissues and organs within the developing embryo.

Relative analgesic potencies of ropivacaine and bupivacaine for epidural analgesia in labor: implications for therapeutic indexes

BACKGROUND

The minimum local analgesic concentration (MLAC) has been defined as the median effective local analgesic concentration in a 20-ml volume for epidural analgesia in the first stage of labor. The aim of this study was to assess the relative analgesic potencies of epidural bupivacaine and ropivacaine by determining their respective minimum local analgesic concentrations.

METHODS

Seventy-three parturients at < or = 7 cm cervical dilation who requested epidural analgesia were allocated to one of two groups in this double-blinded, randomized, prospective study. After a lumbar epidural catheter was placed, 20 ml of the test solution was given, either ropivacaine (n = 34) or bupivacaine (n = 39). The concentration of local anesthetic was determined by the response of the previous patient in that group to a higher or lower concentration using up-down sequential allocation. Analgesic efficacy was assessed using 100-mm visual analog pain scores with < or = 10 mm within 30 min defined as effective. An effective result directed a 0.01% wt/vol decrement for the next patient. An ineffective result directed a 0.01% wt/vol increment.

RESULTS

The minimum local analgesic concentration of ropivacaine was 0.111% wt/vol (95% confidence interval, 0.100-0.122), and the minimum local analgesic concentration of bupivacaine was 0.067% wt/vol (95% confidence interval, 0.052-0.082). Ropivacaine was significantly less potent than bupivacaine, with a potency ratio of 0.6 (95% confidence interval, 0.49-0.74). No difference in motor effects was observed.

CONCLUSION

Ropivacaine was significantly less potent than bupivacaine for epidural analgesia in the first stage of labor.

Oral granisetron for strabismus surgery in children

PURPOSE

To determine the efficacy of oral granisetron in preventing postoperative vomiting (POV) following strabismus repair in children.

METHODS

In a randomized, double-blind, placebo-controlled trial, 73 pediatric patients received either placebo, 20 micrograms.kg-1 or 40 micrograms.kg-1 granisetron po 20 min before induction of anesthesia. No premedication was given, induction was with halothane and all children breathed spontaneously via a laryngeal mask airway. Maintenance was with isoflurane without the use of opioids. Ketorolac and acetaminophen were used for analgesia. The number of episodes and the severity of vomiting and retching were recorded for the first 24 hr postoperatively, as was the use of rescue antiemetics.

RESULTS

Granisetron 20 micrograms.kg-1 and 40 micrograms.kg-1 were more effective than placebo in reducing the incidence of POV during the first 24 hr (29% in both the granisetron groups vs 84% in the placebo group, P < 0.05). In addition, the number of children experiencing severe vomiting (> or = 3 episodes) was reduced in the granisetron 20 micrograms.kg-1 and 40 micrograms.kg-1 groups compared with placebo (4%, 8% and 48% respectively, P < 0.05). Patients in the granisetron group were discharged home earlier (105 min vs 124 min, P = 0.04). There was no difference in the incidence of POV between the two granisetron groups.

CONCLUSION

Preoperative oral granisetron in a dose of 20 micrograms.kg-1 provided effective prophylaxis against POV in children undergoing stabismus repair.

Ratio encoding combinatorial libraries with stable isotopes and their utility in pharmaceutical research

Combinatorial libraries are an important tool for lead discovery in the pharmaceutical industry. Advances in high throughput screening coupled with combinatorial chemistry can significantly reduce the time to find lead compounds. A major difficulty in developing large combinatorial libraries is the ability to identify active compounds. This paper describes a rapid and sensitive encoding/decoding methodology that utilizes stable isotopes and mass spectrometry. The ability of mass spectrometry to precisely determine the intensity of isotopic abundances provides a unique encoding strategy employing synthetically generated ratios of stable isotopes in a compound as the code. The application of ratio encoding is demonstrated using peptoid and imidazole chemistries. Supporting data demonstrate that the incorporation of one or more stable isotopes using unique-predetermined ratios can encode chemical libraries. In addition, the presence of a unique isotopic pattern in a ligand can facilitate the pharmacokinetic analysis. Isotope incorporation into a compound and subsequently into its metabolites reliably distinguishes products from other molecules in the mass spectrum. This is illustrated by metabolic analyses of peptoid and imidazole compounds.

Expression of a gene trap reporter construct in a subset of cells in embryonic sites of hematopoiesis: evidence for alternative rRNA production in hematopoietic cells

Three mouse lines were generated from independent gene trap events in embryonic stem cells. These lines express a betageo reporter gene in a subset of cells at sites of embryonic hematopoiesis. The 5' breakpoints of all three lines were found to lie in 45S ribosomal RNA transcription units. Expression was apparently linked to metabolic activity in these cells, since the kinetics of expression during embryogenesis matched that of cycling cells with colony forming unit spleen (CFU-S) potential. Expression was not seen in adult tissues unless the animals were treated with hydroxyurea, inducing synchronous entry of quiescent CFU-S into the cell cycle. Our results suggest that there is a subset of hematopoietic stem cells, which when actively proliferating, express the SAbetageo reporter construct from RNA polymerase I transcription units.

Dose-dependent reduction of the minimum local analgesic concentration of bupivacaine by sufentanil for epidural analgesia in labor

BACKGROUND

The minimum local analgesic concentration (MLAC) has been defined as the median effective local analgesic concentration in a 20-ml volume for epidural analgesia in the first stage of labor. The aim of this study was to determine the local anesthetic-sparing efficacy of epidural sufentanil by its effect on the MLAC of bupivacaine.

METHODS

In this double-blind, randomized, prospective study, 147 parturients at < or = 7 cm cervical dilation who requested epidural analgesia were allocated to one of four study groups. After a lumbar epidural catheter was placed, study participants received 20 ml bupivacaine (n = 38), bupivacaine with sufentanil 0.5 microg/ml (n = 38), bupivacaine with sufentanil 1 microg/ml (n = 33), or bupivacaine with sufentanil 1.5 microg/ml (n = 38). The concentration of bupivacaine was determined by the response of the previous patient using up-down sequential allocation. The analgesic efficacy was assessed using 100-mm visual analog pain scores, with < or = 10 mm within 30 min defined as effective.

RESULTS

The MLAC of bupivacaine alone was 0.104% wt/vol (95% CI, 0.090-0.117). The addition of sufentanil at doses of 0.5 microg/ml, 1 microg/ml, and 1.5 microg/ml resulted in significant reductions (P < 0.0001) in the MLAC of bupivacaine to 0.048% wt/vol (95% CI, 0.030- 0.065), 0.021% wt/vol (95% CI, 0-0.055), and 0.009% wt/vol (95% CI, 0-0.023), respectively.

CONCLUSIONS

This study showed a significant (P < 0.0001) dose-dependent reduction in the MLAC ofbupivacaine by sufentanil.

A multidimensional approach to protein characterization

When mass spectrometry (MS) is used to study protein primary structure, it is used in a "static" mode. That is, the information is derived from a single MS or MS-MS spectrum. Information about more complex protein structure or protein interactions can also be gained via MS. If a series of mass spectra is collected as something else in the experiment is changing, we increase the "dimensionality" of the MS data. For example, measuring mass spectra as a function of time after exposure of a protein to deuterated solvents can provide information about protein structure. Likewise, by measuring mass spectra of a protein as the concentration of a binding ligand is changed, one can infer the stoichiometry of the complex. Another important, but fundamentally different way of increasing the dimensionality of mass spectral data is by coupling the mass spectrometer to a one- or two-dimensional separation technique.

Wild-type myoblasts rescue the ability of myogenin-null myoblasts to fuse in vivo

Skeletal muscle is formed via a complex series of events during embryogenesis. These events include commitment of mesodermal precursor cells, cell migration, cell-cell recognition, fusion of myoblasts, activation of structural genes, and maturation. In mice lacking the bHLH transcription factor myogenin, myoblasts are specified and positioned correctly, but few fuse to form multinucleated fibers. This indicates that myogenin is critical for the fusion process and subsequent differentiation events of myogenesis. To further define the nature of the myogenic defects in myogenin-null mice, we investigated whether myogenin-null myoblasts are capable of fusing with wild-type myoblasts in vivo using chimeric mice containing mixtures of myogenin-null and wild-type cells. Chimeric embryos demonstrated that myogenin-null myoblasts readily fused in the presence of wild-type myoblasts. However, chimeric myofibers did not express wild-type levels of muscle-specific gene products, and myofibers with a high percentage of mutant nuclei appeared abnormal, suggesting that the wild-type nuclei could not fully rescue mutant nuclei in the myofibers. These data demonstrate that myoblast fusion can be uncoupled from complete myogenic differentiation and that myogenin regulates a specific subset of genes with diverse function. Thus, myogenin appears to control not only transcription of muscle structural genes but also the extracellular environment in which myoblast fusion takes place. We propose that myogenin regulates the expression of one or more extracellular or cell surface proteins required to initiate the muscle differentiation program.

Isotope or mass encoding of combinatorial libraries

BACKGROUND

Combinatorial chemistry using solid-phase synthesis is a rapidly developing technology that can result in a significant reduction in the time required to find and optimize lead compounds. The application of this approach to traditional medicinal chemistry has led to the construction of libraries of small organic molecules on resin beads. A major difficulty in developing large combinatorial libraries is the lack of a facile encoding and decoding methodology to identify active compounds.

RESULTS

Several encoding schemes are described which use the ability of mass spectrometry to ascertain isotopic distributions. Molecular tags are attached to resin beads in parallel or on the linker used for chemical library synthesis. The tags are encoded via a controlled ratio of a number of stable isotopes on the tagging molecules, and range from a single to a complex isotopic distribution.

CONCLUSIONS

A novel coding scheme is described that is useful for the generation of large encoded combinatorial libraries. The code can be cleaved after assay and analyzed by mass spectrometry in an automated fashion. An important element of the combinatorial discovery process is the ability to extract the structure-activity relationship (SAR) information made available by library screening. The speed and sensitivity of the mass-encoding scheme has the potential to determine the full SAR for a given library.

POU domain factor Brn-3b is required for the development of a large set of retinal ganglion cells

The three members of the Brn-3 family of POU domain transcription factors are found in highly restricted sets of central nervous system neurons. Within the retina, these factors are present only within subsets of ganglion cells. We show here that in the developing mouse retina, Brn-3b protein is first observed in presumptive ganglion cell precursors as they begin to migrate from the zone of dividing neuroblasts to the future ganglion cell layer, and that targeted disruption of the Brn-3b gene leads in the homozygous state to a selective loss of 70% of retinal ganglion cells. In Brn-3b (-/-) mice other neurons within the retina and brain are minimally or not at all affected. These experiments indicate that Brn-3b plays an essential role in the development of specific ganglion cell types.

Rescue of early embryonic lethality in mdm2-deficient mice by deletion of p53

The gene p53 encodes a transcriptional activator of genes involved in growth arrest, DNA repair and apoptosis. Loss of p53 function contributes to tumour development in vivo. The transcriptional activation function of p53 is inactivated by interaction with the mdm2 gene product. Amplification of mdm2 has been observed in 36% of human sarcomas, indicating that it may represent an alternative mechanism of preventing p53 function in tumour development. To study mdm2 function in vivo, we generated an mdm2 null allele by homologous recombination. Mdm2 null mice are not viable, and further analysis revealed embryonic lethality around implantation. To examine the importance of the interaction of MDM2 with p53 in vivo, we crossed mice heterozygous for mdm2 and p53 and obtained progeny homozygous for both p53 and mdm2 null alleles. Rescue of the mdm2-/- lethality in a p53 null background suggests that a critical in vivo function of MDM2 is the negative regulation of p53 activity.

Reduction mammaplasty: an outcome analysis

Reduction mammaplasty is usually performed to relieve painful symptoms and physical signs of macromastia. Justification for reduction mammaplasty should be based on the probability of relieving these clinical signs and symptoms. This retrospective study involved four surgeons who performed a variety of breast reduction procedures and was designed to determine if preoperative symptoms were resolved after reduction mammaplasty. We surveyed 285 women who had reduction mammaplasties from 1988 to 1993. Data from these surveys and the patients' charts were reviewed. A total of 185 patients (65%) returned completed surveys and were included in this study for analysis. Mean age was 40 years with an average follow-up of 3 years. The most common preoperative complaint was shoulder grooving (90%), followed by back pain (82%), shoulder pain (78%), and neck pain (65%). Average amount of breast tissue removed was 855 gm from each breast. Preoperative complaints were substantially reduced after surgery, regardless of the presurgical body mass. Most patients (97%) had improvement of symptoms, and 59% were asymptomatic. Only 3% had no change in their symptoms and none were worse. The complication rate was 45% with fat necrosis/infection being the most common complication (22%). The majority of patients (95%) were either happy or very happy with the surgery, and 98% would recommend surgery to a friend. Our data indicate that reduction mammaplasty relieves preoperative symptoms associated with macromastia.

A single-bead decode strategy using electrospray ionization mass spectrometry and a new photolabile linker: 3-amino-3-(2-nitrophenyl)propionic acid

A new linker that employs a photosensitive 3-amino-3-(2-nitrophenyl)propionyl functionality (ANP-resin) has been developed for the preparation of C-terminal carboxamides. A wide range of carboxamides were prepared and identified using the ANP-resin and electrospray ionization mass spectrometry. A single bead containing tripeptide Fmoc-Asp-Arg(Tos)-Val-NH2 was isolated, photocleaved and the peptide was characterized by tandem mass spectrometry, thereby verifying a library decode strategy that avoids complex tagging procedures.

Self-association of a synthetic peptide from the N terminus of the hepatitis delta virus protein into an immunoreactive alpha-helical multimer

The formation of hepatitis delta antigen (HDAg) multimers is required for full biologic activity of this protein and for replication of the hepatitis delta virus. To determine the residues responsible for multimerization, three peptides [ delta 12-49, delta 25-60(Y), delta 12-60(Y)] from the putative coiled-coil multimer-forming domain of HDAg were chemically synthesized and biophysically characterized by circular dichroic spectroscopy, deuterium-exchange mass spectrometry, gel filtration, chemical crosslinking, and ultracentrifugation. By circular dichroism the 50-residue peptide delta 12-60(Y) was half-denatured above 80 degrees C and was 97% alpha-helical at 5 degrees C and 84% alpha-helical at 37 degrees C. By deuterium exchange, peptide delta 12-60(Y) was 93% alpha-helical at 25 degrees C. Its high alpha-helicity and melting temperature are due to the formation of an alpha-helical multimer consisting of four or more chains. All three synthetic peptides reacted with human anti-HDAg antibodies in an enzyme-linked immunosorbent assay, but only peptide delta 12-60(Y) was detected in a sandwich radioimmunoassay in which successful antigens must display at least two antibody-binding sites, which correlates with the ability of this peptide to form multimers. Peptide delta 12-60(Y) also interfered with the self-association of natural HDAg into multimers. These results have significant practical implications for development of improved diagnostic tests, antiviral agents, and possibly even vaccines for prevention of hepatitis delta virus disease.

Deuterium exchange of alpha-helices and beta-sheets as monitored by electrospray ionization mass spectrometry

Deuterium exchange was monitored by electrospray ionization mass spectrometry (ESI-MS) to study the slowly exchanging (hydrogen bonded) peptide hydrogens of several alpha-helical peptides and beta-sheet proteins. Polypeptides were synthetically engineered to have mainly disordered, alpha-helical, or beta-sheet structure. For 3 isomeric 31-residue alpha-helical peptides, the number of slowly exchanging hydrogens as measured by ESI-MS in 50% CF3CD2OD (pD 9.5) provided estimates of their alpha-helicities (26%, 40%, 94%) that agreed well with the values (17%, 34%, 98%) measured by circular dichroic spectroscopy in the same nondeuterated solvent. For 3 betabellins containing a pair of beta-sheets and a related disordered peptide, their order of structural stability (12D > 12S > 14D > 14S) shown by their deuterium exchange rates in 10% CD3OD/0.5% CD3CO2D (pD 3.8) as measured by ESI-MS was the same as their order of structural stability to unfolding with increasing temperature or guanidinium chloride concentration as measured by circular dichroic spectroscopy in water. Compared to monitoring deuterium exchange by proton NMR spectrometry, monitoring deuterium exchange by ESI-MS requires much less sample (1-50 micrograms), much shorter analysis time (10-90 min), and no chemical quenching of the exchange reaction.

The mass spectrometry of helical unfolding in peptides

Two model peptides, melittin and a growth hormone releasing factor (GRF) analog, have been studied by mass spectrometry and tandem mass spectrometry during the course of their deuterium exchange. Both peptides are known from previous work to form α-helices in solution. When the peptides are exposed to deuterated solvents, their masses increase as deuterium atoms replace protons in the exchangeable sites of the peptides. The mass spectrometry results clearly indicate multiple populations of exchangeable protons: Some exchange very fast, and are presumably on the surface and not involved in hydrogen bonding; others exchange much more slowly, indicating that they are probably participating in hydrogen bonding.Tandem mass spectrometric experiments were conducted, and the masses of the product (fragment) ions were used to determine where in the peptide the deuterium atoms were incorporated. The results agree very well with NMR studies of the same peptides. Melittin appears as two helical segments with a kink around Pro-14. The GRF analog contains a single long helix, spanning almost the entire length of the peptide. The dynamics of the unfolding of the helices can also be explored by observing how the exchange progresses with time.