871 research outputs found
The Endoderm Plays an Important Role in Patterning the Segmented Pharyngeal Region in Zebrafish (Danio rerio)
AbstractThe development of the vertebrate head is a highly complex process involving tissues derived from all three germ layers. The endoderm forms pharyngeal pouches, the paraxial mesoderm gives rise to endothelia and muscles, and the neural crest cells, which originate from the embryonic midbrain and hindbrain, migrate ventrally to form cartilage, connective tissue, sensory neurons, and pigment cells. All three tissues form segmental structures: the hindbrain compartmentalizes into rhombomeres, the mesoderm into somitomeres, and the endoderm into serial gill slits. It is not known whether the different segmented tissues in the head develop by the same molecular mechanism or whether different pathways are employed. It is also possible that one tissue imposes segmentation on the others. Most recent studies have emphasized the importance of neural crest cells in patterning the head. Neural crest cells colonize the segmentally arranged arches according to their original position in the brain and convey positional information from the hindbrain into the periphery. During the screen for mutations that affect embryonic development of zebrafish, one mutant, called van gogh (vgo), in which segmentation of the pharyngeal region is absent, was isolated. In vgo, even though hindbrain segmentation is unaffected, the pharyngeal endoderm does not form reiterated pouches and surrounding mesoderm is not patterned correctly. Accordingly, migrating neural crest cells initially form distinct streams but fuse when they reach the arches. This failure to populate distinct pharyngeal arches is likely due to the lack of pharyngeal pouches. The results of our analysis suggest that the segmentation of the endoderm occurs without signaling from neural crest cells but that tissue interactions between the mesendoderm and the neural crest cells are required for the segmental appearance of the neural crest-derived cartilages in the pharyngeal arches. The lack of distinct patches of neural crest cells in the pharyngeal region is also seen in mutants of one-eyed pinhead and casanova, which are characterized by a lack of endoderm, as well as defects in mesodermal structures, providing evidence for the important role of the endoderm and mesoderm in governing head segmentation
Rapid mapping of visual receptive fields by filtered back-projection: application to multi-neuronal electrophysiology and imaging
Neurons in the visual system vary widely in the spatiotemporal properties of their receptive fields (RFs), and understanding these variations is key to elucidating how visual information is processed. We present a new approach for mapping RFs based on the filtered back projection (FBP), an algorithm used for tomographic reconstructions. To estimate RFs, a series of bars were flashed across the retina at pseudo‐random positions and at a minimum of five orientations. We apply this method to retinal neurons and show that it can accurately recover the spatial RF and impulse response of ganglion cells recorded on a multi‐electrode array. We also demonstrate its utility for in vivo imaging by mapping the RFs of an array of bipolar cell synapses expressing a genetically encoded Ca2+ indicator. We find that FBP offers several advantages over the commonly used spike‐triggered average (STA): (i) ON and OFF components of a RF can be separated; (ii) the impulse response can be reconstructed at sample rates of 125 Hz, rather than the refresh rate of a monitor; (iii) FBP reveals the response properties of neurons that are not evident using STA, including those that display orientation selectivity, or fire at low mean spike rates; and (iv) the FBP method is fast, allowing the RFs of all the bipolar cell synaptic terminals in a field of view to be reconstructed in under 4 min. Use of the FBP will benefit investigations of the visual system that employ electrophysiology or optical reporters to measure activity across populations of neurons
Optimizing information flow in small genetic networks. II: Feed forward interactions
Central to the functioning of a living cell is its ability to control the
readout or expression of information encoded in the genome. In many cases, a
single transcription factor protein activates or represses the expression of
many genes. As the concentration of the transcription factor varies, the target
genes thus undergo correlated changes, and this redundancy limits the ability
of the cell to transmit information about input signals. We explore how
interactions among the target genes can reduce this redundancy and optimize
information transmission. Our discussion builds on recent work [Tkacik et al,
Phys Rev E 80, 031920 (2009)], and there are connections to much earlier work
on the role of lateral inhibition in enhancing the efficiency of information
transmission in neural circuits; for simplicity we consider here the case where
the interactions have a feed forward structure, with no loops. Even with this
limitation, the networks that optimize information transmission have a
structure reminiscent of the networks found in real biological systems
Morphological Identification of Parasites Found in Ducks (Family Anatidae) Along the Mississippi River: A Parasitology Class Project
Ducks (Anatidae) can be found across much of the United States and are hosts to a variety of parasites such as nematodes, trematodes or cestodes. This study focused on identifying the species of the parasites found within ducks based on their morphological features. The morphological structures consisted of body shape, internal organs, mouthparts, and length. The ducks used in this study were legally harvested and donated by hunters from areas across the Mississippi River in Buffalo County and Trempealeau County Wisconsin. A total of 108 ducks have been analyzed for parasites. It is important to identify the types of parasites that use ducks as a host, to see if they are harmful to the ducks so that they can be better managed. Necropsy was performed on different species of ducks to extract endo and ectoparasites. The extracted parasites were stained using carmine borax so they could be viewed using microscopy. While examining the parasites under the microscope, length and width measurements were taken as well as identifying key features like hold fast organs. A published key was used as a guide to identify parasites based on the measurements and key features present. The identified parasites were compared with DNA analysis from another research group to help ensure that the identification of the parasites was correct. Finally, identifications were compared to published articles containing past research found on parasites in ducks
Effect of lighting conditions on zebrafish growth and development
In the underwater environment, the properties of light (intensity and spectrum) change rapidly with depth and water quality. In this article, we have described how and to what extent lighting conditions can influence the development, growth, and survival of zebrafish. Fertilized eggs and the corresponding larvae were exposed to different visible light wavelengths (violet, blue, green, yellow, red, and white) in a 12-h light-12-h dark (LD) cycle until 30 days posthatching (dph), when the expression of morphometric parameters and growth (igf1a, igf2a)- and stress-related (crh and pomca) genes were examined. Another group of larvae was raised under constant darkness (DD) until 5 or 10 dph, after which they were transferred to a LD of white light. A third group remained under DD to investigate the effects of light deprivation upon zebrafish development. The results revealed that the hatching rate was highest under blue and violet light, while total length at 30 dph was greatest under blue, white, and violet light. Red light led to reduced feeding activity and poor survival (100% mortality). Larvae raised under constant white light (LL) showed a higher proportion of malformations, as did larvae raised under LD violet light. The expression of growth and stress factors was upregulated in the violet (igf1a, igf2a, pomca, and chr) and blue (igf2a) groups, which is consistent with the higher growth recorded and the higher proportion of malformations detected under the violet light. All larvae kept under DD died before 18 dph, but the survival rates improved in larvae transferred to LD at 5 dph and at 10 dph. In summary, these findings revealed that lighting conditions are crucial factors influencing zebrafish larval development and growth
Effects of Cyclin Dependent Kinase 9 inhibition on zebrafish larvae
CDK9 is a known regulator of cellular transcription, growth and proliferation. Small molecule inhibitors are currently being developed and assessed in clinical trials as anti-cancer drugs. The zebrafish embryo provides an ideal model to explore the effects of CDK9 inhibition in-vivo. This has not been adequately explored previously at the level of a whole organism. We have compared and contrasted the effects of pharmacological and molecular inhibition of CDK9 on somatic growth, apoptosis and cellular proliferation in zebrafish larvae between 0 to 120 hours post fertilisation (hpf) using flavopiridol, a selective CDK9 antagonist, and CDK9-targeting morpholino. We demonstrate that the inhibition of CDK9 diminishes cellular proliferation and increases apoptosis. Subsequently, it affects somatic growth and development of a number of key embryonic structures including the brain, heart, eye and blood vessels. For the first time, we have localized CDK9 at a subcellular level in whole-mounted larvae. This works shows, at a high-throughput level, that CDK9 clearly plays a fundamental role in early cellular growth and proliferation
Lateral Gene Expression in Drosophila Early Embryos Is Supported by Grainyhead-Mediated Activation and Tiers of Dorsally-Localized Repression
The general consensus in the field is that limiting amounts of the transcription factor Dorsal establish dorsal boundaries of genes expressed along the dorsal-ventral (DV) axis of early Drosophila embryos, while repressors establish ventral boundaries. Yet recent studies have provided evidence that repressors act to specify the dorsal boundary of intermediate neuroblasts defective (ind), a gene expressed in a stripe along the DV axis in lateral regions of the embryo. Here we show that a short 12 base pair sequence (“the A-box”) present twice within the ind CRM is both necessary and sufficient to support transcriptional repression in dorsal regions of embryos. To identify binding factors, we conducted affinity chromatography using the A-box element and found a number of DNA-binding proteins and chromatin-associated factors using mass spectroscopy. Only Grainyhead (Grh), a CP2 transcription factor with a unique DNA-binding domain, was found to bind the A-box sequence. Our results suggest that Grh acts as an activator to support expression of ind, which was surprising as we identified this factor using an element that mediates dorsally-localized repression. Grh and Dorsal both contribute to ind transcriptional activation. However, another recent study found that the repressor Capicua (Cic) also binds to the A-box sequence. While Cic was not identified through our A-box affinity chromatography, utilization of the same site, the A-box, by both factors Grh (activator) and Cic (repressor) may also support a “switch-like” response that helps to sharpen the ind dorsal boundary. Furthermore, our results also demonstrate that TGF-β signaling acts to refine ind CRM expression in an A-box independent manner in dorsal-most regions, suggesting that tiers of repression act in dorsal regions of the embryo
Predicting Phenotypic Diversity and the Underlying Quantitative Molecular Transitions
During development, signaling networks control the formation of multicellular patterns. To what extent quantitative fluctuations in these complex networks may affect multicellular phenotype remains unclear. Here, we describe a computational approach to predict and analyze the phenotypic diversity that is accessible to a developmental signaling network. Applying this framework to vulval development in C. elegans, we demonstrate that quantitative changes in the regulatory network can render ~500 multicellular phenotypes. This phenotypic capacity is an order-of-magnitude below the theoretical upper limit for this system but yet is large enough to demonstrate that the system is not restricted to a select few outcomes. Using metrics to gauge the robustness of these phenotypes to parameter perturbations, we identify a select subset of novel phenotypes that are the most promising for experimental validation. In addition, our model calculations provide a layout of these phenotypes in network parameter space. Analyzing this landscape of multicellular phenotypes yielded two significant insights. First, we show that experimentally well-established mutant phenotypes may be rendered using non-canonical network perturbations. Second, we show that the predicted multicellular patterns include not only those observed in C. elegans, but also those occurring exclusively in other species of the Caenorhabditis genus. This result demonstrates that quantitative diversification of a common regulatory network is indeed demonstrably sufficient to generate the phenotypic differences observed across three major species within the Caenorhabditis genus. Using our computational framework, we systematically identify the quantitative changes that may have occurred in the regulatory network during the evolution of these species. Our model predictions show that significant phenotypic diversity may be sampled through quantitative variations in the regulatory network without overhauling the core network architecture. Furthermore, by comparing the predicted landscape of phenotypes to multicellular patterns that have been experimentally observed across multiple species, we systematically trace the quantitative regulatory changes that may have occurred during the evolution of the Caenorhabditis genus
Homeotic Evolution in the Mammalia: Diversification of Therian Axial Seriation and the Morphogenetic Basis of Human Origins
Despite the rising interest in homeotic genes, little has been known about the course and pattern of evolution of homeotic traits across the mammalian radiation. An array of emerging and diversifying homeotic gradients revealed by this study appear to generate new body plans and drive evolution at a large scale.This study identifies and evaluates a set of homeotic gradients across 250 extant and fossil mammalian species and their antecedents over a period of 220 million years. These traits are generally expressed as co-linear gradients along the body axis rather than as distinct segmental identities. Relative position or occurrence sequence vary independently and are subject to polarity reversal and mirroring. Five major gradient modification sets are identified: (1)--quantitative changes of primary segmental identity pattern that appeared at the origin of the tetrapods ; (2)--frame shift relation of costal and vertebral identity which diversifies from the time of amniote origins; (3)--duplication, mirroring, splitting and diversification of the neomorphic laminar process first commencing at the dawn of mammals; (4)--emergence of homologically variable lumbar lateral processes upon commencement of the radiation of therian mammals and ; (5)--inflexions and transpositions of the relative position of the horizontal septum of the body and the neuraxis at the emergence of various orders of therian mammals. Convergent functional changes under homeotic control include laminar articular engagement with septo-neural transposition and ventrally arrayed lumbar transverse process support systems.Clusters of homeotic transformations mark the emergence point of mammals in the Triassic and the radiation of therians in the Cretaceous. A cluster of homeotic changes in the Miocene hominoid Morotopithecus that are still seen in humans supports establishment of a new "hominiform" clade and suggests a homeotic origin for the human upright body plan
The Drosophila Mitochondrial Translation Elongation Factor G1 Contains a Nuclear Localization Signal and Inhibits Growth and DPP Signaling
Mutations in the human mitochondrial elongation factor G1 (EF-G1) are recessive lethal and cause death shortly after birth. We have isolated mutations in iconoclast (ico), which encodes the highly conserved Drosophila orthologue of EF-G1. We find that EF-G1 is essential during fly development, but its function is not required in every tissue. In contrast to null mutations, missense mutations exhibit stronger, possibly neomorphic phenotypes that lead to premature death during embryogenesis. Our experiments show that EF-G1 contains a secondary C-terminal nuclear localization signal. Expression of missense mutant forms of EF-G1 can accumulate in the nucleus and cause growth and patterning defects and animal lethality. We find that transgenes that encode mutant human EF-G1 proteins can rescue ico mutants, indicating that the underlying problem of the human disease is not just the loss of enzymatic activity. Our results are consistent with a model where EF-G1 acts as a retrograde signal from mitochondria to the nucleus to slow down cell proliferation if mitochondrial energy output is low
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