Showing 121 - 130 of 257 Items
Hedgehog signaling is required at multiple stages of zebrafish tooth development
Date: 2010-12-02
Creator: William R. Jackman, James J. Yoo, David W. Stock
Access: Open access
- Background. The accessibility of the developing zebrafish pharyngeal dentition makes it an advantageous system in which to study many aspects of tooth development from early initiation to late morphogenesis. In mammals, hedgehog signaling is known to be essential for multiple stages of odontogenesis; however, potential roles for the pathway during initiation of tooth development or in later morphogenesis are incompletely understood. Results. We have identified mRNA expression of the hedgehog ligands shha and the receptors ptc1 and ptc2 during zebrafish pharyngeal tooth development. We looked for, but did not detect, tooth germ expression of the other known zebrafish hedgehog ligands shhb, dhh, ihha, or ihhb, suggesting that as in mammals, only Shh participates in zebrafish tooth development. Supporting this idea, we found that morphological and gene expression evidence of tooth initiation is eliminated in shha mutant embryos, and that morpholino antisense oligonucleotide knockdown of shha, but not shhb, function prevents mature tooth formation. Hedgehog pathway inhibition with the antagonist compound cyclopamine affected tooth formation at each stage in which we applied it: arresting development at early stages and disrupting mature tooth morphology when applied later. These results suggest that hedgehog signaling is required continuously during odontogenesis. In contrast, over-expression of shha had no effect on the developing dentition, possibly because shha is normally extensively expressed in the zebrafish pharyngeal region. Conclusion. We have identified previously unknown requirements for hedgehog signaling for early tooth initiation and later morphogenesis. The similarity of our results with data from mouse and other vertebrates suggests that despite gene duplication and changes in the location of where teeth form, the roles of hedgehog signaling in tooth development have been largely conserved during evolution. © 2010 Jackman et al; licensee BioMed Central Ltd.
The first formed tooth serves as a signalling centre to induce the formation of the dental row in zebrafish
Date: 2019-06-12
Creator: Yann Gibert, Eric Samarut, Megan K. Ellis, William R. Jackman, Vincent, Laudet
Access: Open access
- The diversity of teeth patterns in actinopterygians is impressive with tooth rows in many locations in the oral and pharyngeal regions. The first-formed tooth has been hypothesized to serve as an initiator controlling the formation of the subsequent teeth. In zebrafish, the existence of the first tooth (named 4 V1) is puzzling as its replacement is induced before the opening of the mouth. Functionally, it has been shown that 4 V1 formation requires fibroblast growth factor (FGF) and retinoic acid (RA) signalling. Here, we show that the ablation of 4 V1 prevents the development of the dental row demonstrating its dependency over it. If endogenous levels of FGF and RA are restored after 4 V1 ablation, embryonic dentition starts again by de novo formation of a first tooth, followed by the dental row. Similarly, induction of anterior ectopic teeth induces subsequent tooth formation, demonstrating that the initiator tooth is necessary and sufficient for dental row formation, probably via FGF ligands released by 4 V1 to induce the formation of subsequent teeth. Our results show that by modifying the formation of the initiator tooth it is possible to control the formation of a dental row. This could help to explain the diversity of tooth patterns observed in actinopterygians and more broadly, how diverse traits evolved through molecular fine-tuning.
Identifying a distinct developmental module in the zebrafish dentition
Date: 2018-01-01
Creator: Caleb Matthew Gordon
Access: Open access
- In the zebrafish pharynx, the first three teeth to form, 3V1, 4V1, and 5V1, have distinct adult and embryonic morphologies, suggesting that these teeth may form using different developmental pathways. Previous studies of gene expression profiles and mutant phenotypes in 3V1, 4V1, and 5V1 have identified four genes that might be involved in dissociating these tooth modules: pitx2b, eve1, pbx1a, and pbx1b. To determine how the developmental roles of these four genes differ across 3V1, 4V1, and 5V1, and obtain a better understanding of how these three teeth develop, I performed CRISPR/Cas9– mediated knockouts in each of these genes, or analyzed embryos from a stable transgenic mutant line where available, and observed the resulting tooth germs and mineralized tooth structures via fluorescence and confocal microscopy. Preliminary results implicate pitx2 as being required for tooth mineralization, offer a possible role for pbx1a, pbx1b, and eve1 in distinguishing the developmental pathway of 3V1, and suggest that 3V1 constitutes a distinct developmental module within the early ventral dentition.
Structural strengthening of urchin skeletons by collagenous sutural ligaments
Date: 1998-01-01
Creator: Olaf Ellers, Amy S. Johnson, Philip E. Moberg
Access: Open access
- Sea urchin skeletons are strengthened by flexible collagenous ligaments that bind together rigid calcite plates at sutures. Whole skeletons without ligaments (removed by bleaching) broke at lower apically applied forces than did intact, fresh skeletons. In addition, in three-point bending tests on excised plate combinations, sutural ligaments strengthened sutures but not plates. The degree of sutural strengthening by ligaments depended on sutural position; in tensile tests, ambital and adapical sutures were strengthened more than adoral sutures. Adapical sutures, which grow fastest, were also the loosest, suggesting that strengthening by ligaments is associated with growth. In fed, growing urchins, sutures overall were looser than in unfed urchins. Looseness was demonstrated visually and by vibration analysis: bleached skeletons of unfed urchins rang at characteristic frequencies, indicating that sound traveled across tightly fitting sutures; skeletons of fed urchins damped vibrations, indicating loss of vibrational energy across looser sutures. Furthermore, bleached skeletons of fed urchins broke at lower apically applied forces than bleached skeletons of unfed urchins, indicating that the sutures of fed urchins had been held together relatively loosely by sutural ligaments. Thus, the apparently rigid dome-like skeleton of urchins sometimes transforms into a flexible, jointed membrane as sutures loosen and become flexible during growth.
Effects of Arabidopsis wall associated kinase mutations on ESMERALDA1 and elicitor induced ROS
Date: 2021-05-01
Creator: Bruce D. Kohorn, Bridgid E. Greed, Gregory Mouille, Stéphane Verger, Susan L., Kohorn
Access: Open access
- Angiosperm cell adhesion is dependent on interactions between pectin polysaccharides which make up a significant portion of the plant cell wall. Cell adhesion in Arabidopsis may also be regulated through a pectin-related signaling cascade mediated by a putative O-fucosyltransferase ESMERALDA1 (ESMD1), and the Epidermal Growth Factor (EGF) domains of the pectin binding Wall associated Kinases (WAKs) are a primary candidate substrate for ESMD1 activity. Genetic interactions between WAKs and ESMD1 were examined using a dominant hyperactive allele of WAK2, WAK2cTAP, and a mutant of the putative O-fucosyltransferase ESMD1. WAK2cTAP expression results in a dwarf phenotype and activation of the stress response and reactive oxygen species (ROS) production, while esmd1 is a suppressor of a pectin deficiency induced loss of adhesion. Here we find that esmd1 suppresses the WAK2cTAP dwarf and stress response phenotype, including ROS accumulation and gene expression. Additional analysis suggests that mutations of the potential WAK EGF O-fucosylation site also abate the WAK2cTAP phenotype, yet only evidence for an N-linked but not O-linked sugar addition can be found. Moreover, a WAK locus deletion allele has no effect on the ability of esmd1 to suppress an adhesion deficiency, indicating WAKs and their modification are not a required component of the potential ESMD1 signaling mechanism involved in the control of cell adhesion. The WAK locus deletion does however affect the induction of ROS but not the transcriptional response induced by the elicitors Flagellin, Chitin and oligogalacturonides (OGs).
Forces generated during stretch in the heart of the lobster Homarus americanus are anisotropic and are altered by neuromodulators
Date: 2016-01-01
Creator: E. S. Dickinson, A. S. Johnson, O. Ellers, P. S. Dickinson
Access: Open access
- Mechanical and neurophysiological anisotropies mediate three-dimensional responses of the heart of Homarus americanus. Although hearts in vivo are loaded multi-axially by pressure, studies of invertebrate cardiac function typically use uniaxial tests. To generate whole-heart length-tension curves, stretch pyramids at constant lengthening and shortening rates were imposed uniaxially and biaxially along longitudinal and transverse axes of the beating whole heart. To determine whether neuropeptides that are known to modulate cardiac activity in H. americanus affect the active or passive components of these length-tension curves, we also performed these tests in the presence of SGRNFLRFamide (SGRN) and GYSNRNYLRFamide (GYS). In uniaxial and biaxial tests, both passive and active forces increased with stretch along both measurement axes. The increase in passive forces was anisotropic, with greater increases along the longitudinal axis. Passive forces showed hysteresis and active forces were higher during lengthening than shortening phases of the stretch pyramid. Active forces at a given length were increased by both neuropeptides. To exert these effects, neuropeptides might have acted indirectly on the muscle via their effects on the cardiac ganglion, directly on the neuromuscular junction, or directly on the muscles. Because increases in response to stretch were also seen in stimulated motor nerve-muscle preparations, at least some of the effects of the peptides are likely peripheral. Taken together, these findings suggest that flexibility in rhythmic cardiac contractions results from the amplified effects of neuropeptides interacting with the length-tension characteristics of the heart.
Sensory-based niche partitioning in a multiple predator-multiple prey community
Date: 2015-05-20
Creator: Jay J. Falk, Hannah M. Ter Hofstede, Patricia L. Jones, Marjorie M. Dixon, Paul A., Faure, Elisabeth K.V. Kalko, Rachel A. Page
Access: Open access
- Many predators and parasites eavesdrop on the communication signals of their prey. Eavesdropping is typically studied as dyadic predator-prey species interactions; yet in nature, most predators target multiple prey species and most prey must evade multiple predator species. The impact of predator communities on prey signal evolution is not well understood. Predators could converge in their preferences for conspicuous signal properties, generating competition among predators and natural selection on particular prey signal features. Alternatively, predator species could vary in their preferences for prey signal properties, resulting in sensory-based niche partitioning of prey resources. In the Neotropics, many substrate-gleaning bats use the mate-attraction songs of male katydids to locate them as prey. We studied mechanisms of niche partitioning in four substrate- gleaning bat species and found they are similar in morphology, echolocation signal design and prey-handling ability, but each species preferred different acoustic features of male song in 12 sympatric katydid species. This divergence in predator preference probably contributes to the coexistence of many substrate-gleaning bat species in the Neotropics, and the substantial diversity in the mate-attraction signals of katydids. Our results provide insight into how multiple eavesdropping predator species might influence prey signal evolution through sensory-based niche partitioning.
TAKs, thylakoid membrane protein kinases associated with energy transduction
Date: 1999-04-02
Creator: Shaun Snyders, Bruce D. Kohorn
Access: Open access
- The phosphorylation of proteins within the eukaryotic photosynthetic membrane is thought to regulate a number of photosynthetic processes in land plants and algae. Both light quality and intensity influence protein kinase activity via the levels of reductants produced by the thylakoid electron transport chain. We have isolated a family of proteins called TAKs, Arabidopsis thylakoid membrane threonine kinases that phosphorylate the light harvesting complex proteins. TAK activity is enhanced by reductant and is associated with the photosynthetic reaction center II and the cytochrome b6f complex. TAKs are encoded by a gene family that has striking similarity to transforming growth factor β receptors of metazoans. Thus thylakoid protein phosphorylation may be regulated by a cascade of reductant-controlled membrane-bound protein kinases.
The 10kb Drosophila virus 28S rDNA intervening sequence is flanked by a disect repeat of 14 base pairs of coding sequence
Date: 1980-08-25
Creator: Peter M.M. Rae, Bruce D. Kohorn, Robert P. Wade
Access: Open access
- Most repeat units of rDNA in Drosophila virilis are interrupted in the 28S rRNA coding region by an intervening sequence about 10 kb in length; uninterrupted repeats have a length of about 11 kb. We have sequenced the coding/intervening sequence junctions and flanking regions in two independent clones of interrupted rDNA, and the corresponding 28S rRNA coding region in a clone of uninterrupted rDNA. The intervening sequence is terminated at both ends by a direct repeat of a fourteen nucleotide sequence that is present once in the corresponding region of an intact gene. This is a phenomenon associated with transposable elements in other eukaryotes and in prokaryotes, and the Drosophila rDNA intervening sequence is discussed in this context. We have compared more than 200 nucleotides of the D. virilis 28S rRNA gene with sequences of homologous regions of rDNA in Tetrahymena pigmentosa (Wild and Sommer, 1980) and Xenopus laevis (Gourse and Gerbi, 1980): There is 93% sequence homology among the diverse species, so that the rDNA region in question (about two-thirds of the way into the 28S rRNA coding sequence) has been very highly conserved in eukaryote evolution. The intervening sequence in T. pigmentosa is at a site 79 nucleotides upstream from the insertion site of the Drosophila intervening sequence. © 1980 IRL Press Limited.
Disruption of Thylakoid-associated Kinase 1 Leads to Alteration of Light Harvesting in Arabidopsis
Date: 2001-08-24
Creator: Shaun Snyders, Bruce D. Kohorn
Access: Open access
- To survive fluctuations in quality and intensity of light, plants and algae are able to preferentially direct the absorption of light energy to either one of the two photosystems PSI or PSII. This rapid process is referred to as a state transition and has been correlated with the phosphorylation and migration of the light-harvesting complex protein (LHCP) between PSII and PSI. We show here that thylakoid protein kinases (TAKs) are required for state transitions in Arabidopsis. Antisense TAK1 expression leads to a loss of LHCP phosphorylation and a reduction in state transitions. Preferential activation of PSII causes LHCP to accumulate with PSI, and TAK1 mutants disrupt this process. Finally, TAKs also influence the phosphorylation of multiple thylakoid proteins.