Showing papers on "Uca pugilator published in 1999"

Chitobiase activity in the epidermis and hepatopancreas of the fiddler crab Uca pugilator during the molting cycle

Abstract: The activity of chitobiase, also known as N-acetyl-β-glucosaminidase, in the epidermis and hepatopancreas of the fiddler crab Uca pugilator (Bosc, 1802), during the molting cycle, was investigated. A pH optimum of 5 to 6 was found for the enzymatic activity in both the epidermis and hepatopancreas. The temperature optimum for epidermal and hepatopancreatic chitobiase activities was 50 to 60 °C. The K m values for epidermal and hepatopancreatic chitobiase activities at 19 °C were 0.190 ± 0.027 and 0.203 ± 0.016 mM 4-methylumbelliferyl-N-acetyl-β-glucosaminide, respectively. Hepatopancreatic chitobiase activity was significantly higher than epidermal enzymatic activity in all the molt cycle stages tested except Postmolt Stage A-B. Chitobiase activity varied significantly during the molting cycle, with the epidermal enzymatic activity in Premolt Stage D3–4 significantly higher than in Stage C (intermolt) and Premolt Stage D0, whereas hepatopancreatic chitobiase activity in Premolt Stage D3–4 was significantly higher than in all other molt stages tested. The patterns of chitobiase activity in the epidermis and hepatopancreas correlate well with the hemolymph titer of ecdysteroids in U. pugilator during the molting cycle; this suggests that chitobiase activity in both tissues is regulated at least in part by the steroid molting hormones.

Regulatory effects of environmental chemical signals on search behavior and foraging success

Abstract: To appreciate the mechanisms governing olfactory-mediated behavior, pro- cesses of chemical signal production and transmission in fluid media (air or water) must be understood. With new tools becoming available in analytical chemistry and fluid dy- namics, investigators can now quantitatively address the processes governing chemical signals in field habitats. This study identifies the role of amino acids as signal molecules regulating search behavior and foraging success by estuarine mud snails (Ilyanassa ob- soleta). For the first time, methods are described for measuring chemical signal production, release, and transport in field habitats, over temporal and spatial scales consistent with olfactory information processing. Rates of advection and turbulent mixing were determined, and shear velocities and roughness Reynolds numbers were estimated to characterize bottom boundary layer flows. Nearly instantaneous chemical measurements were made using a computerized microprobe system and conservative tracer to establish the environmental distributions of signal molecules at rates similar to those sampled by olfactory receptor neurons. In addition, we determined the dissolved free amino acid (DFAA) compositions (up to 18 amino acids), concentrations, and effluent release rates for live intact and injured fiddler crabs (Uca pugilator) and hard clams (Mercenaria mercenaria), which are common prey from mud snail habitats. The field site populated by mud snails was found to be more conducive at broadcasting stronger chemical signals over longer distances than most other estuarine and ocean habitats. Live fiddler crabs released amino acids at very low fluxes (0.1 nmol-min-'-g (wet tissue aiass)-V), while live intact clams took up amino acids from seawater. Once injured, hard clams and fiddler crabs released DFAAs at 88 and 6804 nmol-min-1-g-1, respectively. Mud snails were significantly attracted to injured clams and crabs, but not to intact prey, as compared with controls. Synthetic mixtures of amino acids, simulating fluids leaking from injured prey, were also highly attractive. When we tested for effects of amino acid composition, concentration, mean volume flow rate (of chemical input), and flux, in separate experiments, only flux directly correlated with the number of mud snails attracted. The attraction of mud snails is thus more tightly coupled to the physical transport of chemical stimuli than to the molecular properties of specific amino acids.

Limb Regeneration in the Fiddler Crab, Uca pugilator: Histological, Physiological and Molecular Considerations

Abstract: Synopsis. This paper summarizes our recent work on the histological, physiolog? ical and molecular aspects of limb regeneration in the fiddler crab Uca pugilator and new information is presented on mitotic activity in the blastema during the first days of blastemal organization. We also report for the first time the locali? zation of vertebrate growth factor immunoreactivity (FGF 2 and FGF 4) in the regenerating blastema. In the first part of this paper we review recent histological findings concerning the physical events that accompany autotomy of limbs and propose a new function for the autotomy membrane?the tethering of the regen? erating pedal nerve to the walls of the coxa. In the second part of the paper we review our recent findings on the identification and characterization of the Uca ecdysteroid receptor (UpEcR, and its potential dimer partner, the retinoid-X-receptor, UpRXR). Using (/ca-specific antibody probes raised in our lab, we have been able to identify specific cells in the early blastema that express receptor pro? teins. The regenerating limb of the fiddler crab is responsive to both steroids and retinoids and mRNA for steroid and retinoid receptors are expressed in the re? generating limb buds during all stages of regeneration. The DNA and deduced amino acid sequences of the ecdysteroid receptor is very similar to the sequences of insect EcRs, while the retinoid receptor is similar to insect protein (ultraspiracle) in the DNA-binding domain, but closer to vertebrate RXRs in the ligand binding domain.

Characterization of ecr and rxr gene homologs and receptor expression during the molt cycle in the crab, uca pugilator

Abstract: Synopsis. Crustaceans have the remarkable ability to regenerate limbs. Unlike insects, crustaceans also continue to increase in body size with age, and new limb regeneration must occur in concert with the growth and reproductive activities of the adult. In the fiddler crab, Uca pugilator, regeneration consists of the formation of a blastema (limb primordium) from cells migrating into the site of the wound. Over a time course related to the physiology and growth cycle of the animal, these cells proliferate and differentiate into an intact miniature limb, which will then increase in size and emerge as a functional appendage with the next molting of the body exoskeleton. In arthropods, changes in gene expression mediating both growth (e.g., cuticular molting) and differentiation (e.g., insect metamorphosis) are regulated by ecdysteroids. We hypothesize that ecdysteroids and their receptors are also involved in the regulation of limb regeneration in crabs. To investigate this hypothesis, clones representing the crustacean ecdysteroid receptor have been isolated and are providing the basis for the development of nucleic acid and immunological probes to identify, at the tissue level, the pattern of receptor expres? sion relative to changes in hormone titer during all stages of regeneration. In support of this hypothesis, we have detected the expression of the nuclear receptor genes encoding the ecdysteroid receptor at the earliest stages of blastemal devel? opment. We have also shown that receptor transcript synthesis can be influenced by external factors (retinoid exposure) which disrupt Uca blastemal differentiation. These studies allow us to identify and characterize putative ecdysteroid target tis? sues. They begin to address the goal of defining how a common signal (e.g., cir? culating hormones) can influence a variety of discrete developmental programs.