spalt-dependent switching between two cell fates that are induced by the Drosophila EGF receptor.
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Signaling from the EGF receptor (EGFR) can trigger the differentiation of a wide variety of cell types in many animal species. We have explored the mechanisms that generate this diversity using the Drosophila peripheral nervous system. In this context, Spitz (SPI) ligand can induce two alternative cell fates from the dorsolateral ectoderm: chordotonal sensory organs and non-neural oenocytes. We show that the overall number of both cell types that are induced is controlled by the degree of EGFR signaling. In addition, the spalt (sal) gene is identified as a critical component of the oenocyte/chordotonal fate switch. Genetic and expression analyses indicate that the SAL zinc-finger protein promotes oenocyte formation and supresses chordotonal organ induction by acting both downstream and in parallel to the EGFR. To explain these findings, we propose a prime-and-respond model. Here, sal functions prior to signaling as a necessary but not sufficient component of the oenocyte prepattern that also serves to raise the apparent threshold for induction by SPI. Subsequently, sal-dependent SAL upregulation is triggered as part of the oenocyte-specific EGFR response. Thus, a combination of SAL in the responding nucleus and increased SPI ligand production sets the binary cell-fate switch in favour of oenocytes. Together, these studies help to explain how one generic signaling pathway can trigger the differentiation of two distinct cell types. (+info)
The novel C. elegans gene sop-3 modulates Wnt signaling to regulate Hox gene expression.
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We describe the properties of a new gene, sop-3, that is required for the regulated expression of a C. elegans Hox gene, egl-5, in a postembryonic neuroectodermal cell lineage. Regulated expression of egl-5 in this cell lineage is necessary for development of the sensory rays of the male tail. sop-3 encodes a predicted novel protein of 1475 amino acids without clear homologs in other organisms. However, the sequence contains motifs consisting of homopolymeric runs of amino acids found in several other transcriptional regulators, some of which also act in Hox gene regulatory pathways. The genetic properties of sop-3 are very similar to those of sop-1, which encodes a component of the transcriptional Mediator complex, and mutations in the two genes are synthetic lethal. This suggests that SOP-3 may act at the level of the Mediator complex in regulating transcription initiation. In a sop-3 loss-of-function background, egl-5 is expressed ectopically in lineage branches that normally do not express this gene. Such expression is dependent on the Hox gene mab-5, as it is in branches where egl-5 is normally expressed. Ectopic egl-5 expression is also dependent on the Wnt pathway. Thus, sop-3 contributes to the combinatorial control of egl-5 by blocking egl-5 activation by MAB-5 and the Wnt pathway in inappropriate lineage branches. (+info)
Strike feeding behavior in the muskellunge, Esox masquinongy: contributions of the lateral line and visual sensory systems.
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The muskellunge, Esox masquinongy, is a predatory esocid fish with well-developed visual and lateral line systems. The purpose of this study was to determine the relative roles of these two sensory modalities in organizing the strike behavior of the animal. Subadult muskellunge were videotaped in a test arena while feeding on fathead minnows (Pimephales promelas). Animals were tested under five conditions: (i) control animals in which the visual and lateral line systems were intact; (ii) animals with lateral line afference suppressed by immersion for 12-24 h in 0.1 mmol l(-1) CoCl2; (iii) animals blinded by bilateral optic nerve transection; (iv) animals that had been unilaterally blinded; and (v) animals in which the lateral line system had been unilaterally denervated. The feeding behavior of the muskellunge consists of two phases: a slow stalk of the prey with minimal body movement followed by an explosive C- or S-start lunge at the prey. Quantitative comparisons of animals in the five test groups indicate that, although vision is used in the initial acquisition of the prey, both vision and the lateral line system play important roles in determining the initiation of the rapid strike. The lateral line system may play a critical role in the final capture of the prey at the end of the strike. In addition, lateral-line-suppressed muskellunge strongly alter their approaches to more distant prey. Bilaterally blinded muskellunge do not stalk their prey, but will lunge only at prey that are at close range. Unilaterally blinded or denervated muskellunge also alter their detection of and approach to prey, attending to a wider region of the intact sensory hemisphere. Our data suggest not only that the visual and lateral line systems play complementary roles in the feeding behavior sequence but also that each system plays a more or less dominant role during consecutive phases of the behavior. (+info)
Costs and the diversification of exaggerated animal structures.
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Sexual selection can favor production of extravagant ornaments and weapons in the contest for access to the opposite sex. Existing explanations for the diversity of sexually selected structures focus on reproductive benefits conferred by particular ornament or weapon morphologies. Here, I show that costs of weapon production also may drive patterns of weapon evolution. In beetles, production of horns reduces the size of neighboring morphological structures (antennae, eyes, or wings, depending on the location of the horns), and these tradeoffs reveal unexpected functional associations between ecology and horn morphology. This study illustrates a critical but overlooked role of costs in sexual selection and has implications for understanding the evolution of animal morphology. (+info)
Neuronal population codes and the perception of object distance in weakly electric fish.
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Weakly electric fish use an electric sense to navigate and capture prey in the dark. Objects in the surroundings of the fish produce distortions in their self-generated electric field; these distortions form a two-dimensional Gaussian-like electric image on the skin surface. To determine the distance of an object, the peak amplitude and width of its electric image must be estimated. These sensory features are encoded by a neuronal population in the early stages of the electrosensory pathway, but are not represented with classic bell-shaped neuronal tuning curves. In contrast, bell-shaped tuning curves do characterize the neuronal responses to the location of the electric image on the body surface, such that parallel two-dimensional maps of this feature are formed. In the case of such two-dimensional maps, theoretical results suggest that the width of neural tuning should have no effect on the accuracy of a population code. Here we show that although the spatial scale of the electrosensory maps does not affect the accuracy of encoding the body surface location of the electric image, maps with narrower tuning are better for estimating image width and those with wider tuning are better for estimating image amplitude. We quantitatively evaluate a two-step algorithm for distance perception involving the sequential estimation of peak amplitude and width of the electric image. This algorithm is best implemented by two neural maps with different tuning widths. These results suggest that multiple maps of sensory features may be specialized with different tuning widths, for encoding additional sensory features that are not explicitly mapped. (+info)
Fluid dynamic design of lobster olfactory organs: high speed kinematic analysis of antennule flicking by Panulirus argus.
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Many organisms use olfactory appendages bearing arrays of microscopic hairs to pick up chemical signals from the surrounding water or air. We report a morphometric and high speed kinematic analysis of the olfactory organs (lateral flagella of the antennules, which bear chemosensory aesthetasc hairs) of the spiny lobster, Panulirus argus. Panulirus argus sample specific locations by executing a rapid series of antennule flicks at one position, moving the antennule to a different spot and then performing another series of flicks. Odorant delivery to an aesthetasc depends on the water motion near it, which depends on its Reynolds number (Re, proportional to both the diameter and speed of the hair). High speed video enabled us to resolve that during a series of flicks, an antennule moves down rapidly (aesthetasc Re = 2) and up more slowly (Re = 0.5), pausing briefly ( approximately 0.54 s) before the next downstroke. The antennules of P. argus operate in a range of Re values and inter-aesthetasc spacings in which penetration of fluid between the hairs in an array is especially sensitive to changes in speed. Therefore, when antennules flick 'old' water is flushed out of the aesthetasc array during the leaky downstroke and is not picked up again during the less leaky upstroke, hence the antennules can take discrete samples. Thus, by operating in this critical Re range these antennules should be particularly effective at sniffing. (+info)
Tantalus, a novel ASX-interacting protein with tissue-specific functions.
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The Drosophila trithorax- and Polycomb-group (trxG and PcG) proteins maintain activated and repressed transcriptional states at specific target gene loci. The Additional sex combs (Asx) gene is of particular interest as it appears to function in both protein complexes and yet its effects on target genes are more restricted. A novel protein, Tantalus (TAN), was identified in a yeast two-hybrid screen for ASX-interacting proteins that might confer tissue-specific ASX functions. TAN contains consensus nuclear localization sites and binds DNA in vitro. However, its subcellular localization varies in a tissue-specific fashion. In salivary glands, TAN is predominantly nuclear and associates with 66 euchromatic sites on polytene chromosomes, more than half of which overlap with ASX. These loci do not include the homeotic genes of the ANT and BX complexes bound by other PcG and trxG proteins. Rather, tan mutant defects are restricted to sensory organs. We show that one of these defects, shared by Asx, is genetically enhanced by Asx. Taken together, the data suggest that TAN is a tissue-specific cofactor for ASX, and that its activity may be partially controlled by subcellular trafficking. (+info)
Spatial regulation of DELTA expression mediates NOTCH signalling for segmentation of Drosophila legs.
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The Notch (N) signalling pathway is recruited for segregation of cell fates in a number of Drosophila tissue types. We show here that N dependent segmentation of Drosophila legs is regulated by a dynamic pattern of expression of its ligand, DELTA (DL). During third larval instar and early stages of pupation, high levels of DL expression is seen in stripes of cells in the leg imaginal discs which later form the proximal borders of leg joints. These domains also displayed heightened Dl enhancer activity. During subsequent stages of pupation, following segmentation of the leg primordium, DL expression becomes uniform throughout these segments barring the joints. We further show that regulatory Dl mutations or mis-expression of DL abolish leg segmentation. Domains of N signalling for segmentation of legs of flies are thus set up by a stringent spatial regulation of expression of its ligand at the segment border. Further, a comparable role of DL in antennal development reveals a common paradigm of DL-N signalling for segmentation of appendages in flies. (+info)