			Home About us Contact

Metamorphic Development (metamorphic + development)

Distribution by Scientific Domains

Life Sciences	83%

Selected Abstracts

Metamorphic inhibition of Xenopus laevis by sodium perchlorate: Effects on development and thyroid histology

ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 4 2005
Joseph E. Tietge
Abstract The perchlorate anion inhibits thyroid hormone (TH) synthesis via inhibition of the sodium-iodide symporter. It is, therefore, a good model chemical to aid in the development of a bioassay to screen chemicals for affects on thyroid function. Xenopus laevis larvae were exposed to sodium perchlorate during metamorphosis, a period of TH-dependent development, in two experiments. In the first experiment, stage 51 and 54 larvae were exposed for 14 d to 16, 63, 250, 1,000, and 4,000 ,g perchlorate/L. In the second experiment, stage 51 larvae were exposed throughout metamorphosis to 8, 16, 32, 63, and 125 ,g perchlorate/L. Metamorphic development and thyroid histology were the primary endpoints examined. Metamorphosis was retarded significantly in the first study at concentrations of 250 ,g/L and higher, but histological effects were observed at 16 ,g/L. In the second study, metamorphosis was delayed by 125 ,g/L and thyroid size was increased significantly at 63 ,g/L. These studies demonstrate that inhibition of metamorphosis readily can be detected using an abbreviated protocol. However, thyroid gland effects occur at concentrations below those required to elicit developmental delay, demonstrating the sensitivity of this endpoint and suggesting that thyroidal compensation is sufficient to promote normal development until perchlorate reaches critical concentrations. [source]

Cell proliferation in the Rana catesbeiana auditory medulla over metamorphic development

DEVELOPMENTAL NEUROBIOLOGY, Issue 2 2006
Judith A. Chapman
Abstract During metamorphic development, bullfrogs (Rana catesbeiana) undergo substantial morphological, anatomical, and physiological changes as the animals prepare for the transition from a fully-aquatic to a semi-terrestrial existence. Using BrdU incorporation and immunohistochemistry, we quantify changes in cell proliferation in two key auditory brainstem nuclei, the dorsolateral nucleus and the superior olivary nucleus, over the course of larval and early postmetamorphic development. From hatchling through early larval stages, numbers of proliferating cells increase in both nuclei, paralleling the overall increase in total numbers of cells available for labeling. Numbers of proliferating cells in the superior olivary nucleus decrease during the late larval and deaf periods, and significantly increase during metamorphic climax. Proliferating cells in the dorsolateral nucleus increase in number from hatchling to late larval stages, decrease during the deaf period, and increase during climax. In both nuclei, numbers of proliferating cells decrease during the postmetamorphic froglet stage, despite increases in the number of cells available for label. Newly generated cells express either glial- or neural-specific phenotypes beginning between 1 week and 1 month post-BrdU injection, respectively, while some new cells express ,-aminobutyric acid within 2 days of mitosis. Our data show that these auditory nuclei dramatically up-regulate mitosis immediately prior to establishment of a transduction system based on atmospheric hearing. © 2005 Wiley Periodicals, Inc. J Neurobiol, 2005 [source]

Critical period of sensitivity for effects of cadmium on frog growth and development,

ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 6 2009
Jackson A. Gross
Abstract Cadmium is a ubiquitous pollutant in aquatic environments that can alter organismal physiology and ecology. Previous experiments found that ecological Cd exposures increased the growth and development of two North American anurans. However, the generality of these effects among species, the time period over which they occur, and the mechanisms responsible remain conjectural. The goal of the present study was to determine the critical period of sensitivity of Rana pipiens exposed to ecologically relevant levels of Cd. We exposed tadpoles to Cd (0 [control], 1.0, and 10.0 ,g/L) from Gosner stage (GS) 25 to metamorphic climax. We assessed effects of Cd on amphibian length, survival, and development during premetamorphosis (GS 25,30) and prometamorphosis (GS 31,42). After 14 d of exposure, we staged tadpoles and recorded snout-vent length. Tadpoles were then pooled according to treatment and stage (GS , 29 or GS , 30) and allowed to undergo metamorphic development. Tadpoles exposed to 10 ,g/L were significantly larger and more advanced in development by 14 d. Survival to forelimb emergence exceeded 90% in all treatments, and time to metamorphic climax was not different from that in controls. Body burdens of Cd were positively correlated with increasing treatment. Early amphibian development (premetamorphosis) was shown to be the critical period of sensitivity for growth and development. Whereas the freshwater criterion for Cd appears to be protective for survival, a lack of knowledge remains about the sublethal effects of chronic exposures of metal pollutants, especially as they relate to tissue concentrations at various stages of amphibian life history. [source]

A teratocyte gene from a parasitic wasp that is associated with inhibition of insect growth and development inhibits host protein synthesis

INSECT MOLECULAR BIOLOGY, Issue 5 2003
D. L. Dahlman
Abstract After parasitization, some wasps induce hosts prematurely to initiate metamorphic development that is then suspended in a postwandering, prepupal state. Following egression of the parasite larva, the host remains in this developmentally arrested state until death. Teratocytes, cells released at egg hatch from extra-embryonic serosal membranes of some wasp parasites, inhibit growth and development when injected into host larvae independent of other parasite factors (e.g. venom, polydnavirus). Synthesis of some developmentally regulated, abundantly expressed Heliothis virescens host proteins is inhibited in hosts parasitized by Microplitis croceipes and by teratocyte injection. A cDNA encoding a 13.9 kDa protein (TSP14) that inhibited protein synthesis, growth and development was isolated from a protein fraction secreted by teratocytes. TSP14 appears to be responsible, in part, for the teratocyte-mediated inhibition of host growth and development. Interestingly, this cDNA encoded a cysteine-rich amino acid motif similar to that described from Campoletis sonorensis polydnavirus, a mutualistic virus that enables wasp parasitization of lepidopteran larvae. Moreover, TSP14 inhibited protein synthesis in a dose-dependent manner in rabbit reticulocyte lysate and wheat germ extract translation systems. We hypothesize that some wasp parasites inhibit translation as a general means to regulate and redirect lepidopteran host physiology to support endoparasite development. [source]

Iodine enrichment of Artemia and enhanced levels of iodine in Atlantic halibut larvae (Hippoglossus hippoglossus L.) fed the enriched Artemia

AQUACULTURE NUTRITION, Issue 2 2006
M. MOREN
Abstract Flatfish metamorphosis is initiated by the actions of thyroid hormones (TH) and iodine is an essential part of these hormones. Hence, an iodine deficiency may lead to insufficient levels of TH and incomplete metamorphosis. In this study, different iodine sources for enrichment of Artemia were evaluated and the levels of iodine obtained in Artemia were within the range of 60,350 ,g g,1 found in copepods. Larval Atlantic halibut was fed Artemia enriched with either normal DC-DHA Selco or DC-DHA Selco (commercial enrichments) supplemented with iodine from days 9 to 60 postfirst feeding. There was no significant difference in growth, mortality or metamorphic development between the groups. The analyses showed that we were able to enrich Artemia with iodine. Further, the larvae-fed iodine-enriched Artemia had higher whole body iodine concentration compared to larvae-fed Artemia without iodine enrichment. [source]