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New internal and external structures are described from unusually well-preserved specimens of the acritarch genus Hoegklintia Doming 1981, recovered from the Lower Silurian Osgood and Estill shales of Kentucky and Estill Shale of Ohio (U.S.A.). The morphological variability of internal features ranges from irregularly dispersed organic remains and clusters of circular bodies within the vesicle, to structures congruent with the contours of the vesicle and processes. External bodies are primarily ovoid, and may have a 'tube-like' extension penetrating the vesicle interior. Published studies mention and/or depict Hoegklintia with dispersed internal organic matter, but the specimens illustrated here are the first to exhibit morphologically discernible contents. Evidence suggests that these various entities represent coagulated cell contents, life-cycle stages, or manifestations of parasitism/mutualism. [ABSTRACT FROM AUTHOR]

In 1996, the U.S. Congress mandated the development of a screening program for endocrine-disrupting chemicals (EDCs) using validated test systems. Subsequently, the Endocrine Disruptor Screening and Testing Advisory Committee recommended the development of a standardized amphibian assay for tier 2 testing of EDCs. For that reason, a tier 2 testing protocol using Xenopus (Silurana) tropicalis and a 30-week, flow-through exposure to the antiandrogen flutamide from stage 46 tadpoles through sexually mature adult frogs were developed and evaluated in this pilot study. The endpoints for this study included measurements of frog body lengths and weights, liver weights, ovary/egg mass weights, testicular and ovarian histopathology, plasma vitellogenin levels, and notes on any abnormalities observed at necropsy. Increasing exposure concentrations to flutamide caused significant increases in frogs with no recognizable gonadal tissue and increased body and liver weights in male frogs, whereas the body lengths and weights decreased significantly in female frogs. Important issues must be resolved before a tier 2 amphibian assay can be further developed and validated, including the establishment of baseline values in the controls for the parameters under study; the maintenance, measurement, and timing of exposure concentrations; and the development of additional biomolecular markers of effect. This study demonstrated the feasibility of conducting long-term EDC exposure studies using X. tropicalis. [ABSTRACT FROM AUTHOR]

Evaluates the effect of pond water and sediment extract samples on Xenopus in New Hampshire. Induction of abnormal embryo-larval and hindlimb development; Growth rate of Xenopus; Metamorphic climax of Xenopus.

More than 90% of a breeding colony of clawed frogs (Xenopus tropicalis)imported to the United States from western Africa died in an epizootic of chlamydiosis. Chlamydial inclusions were observed by light and electron microscopy in the liver of an infected frog. Chlamydia pneumoniae was isolated in cell cultures from four frogs. A cutaneous infection by a chytridiomycete fungus observed in two frogs could have been a cofactor in the die-off. [ABSTRACT FROM AUTHOR]

In previously conducted laboratory studies with the South African clawed frog (Xenopus laevis), pond water and sediment samples collectedfrom various sites in Minnesota, USA, were demonstrated to have the potential to induce a variety of developmental abnormalities, including early embryo-larval maldevelopment, abnormal limb development, anddisruption of metamorphosis. The results of exposure of X. laevis tosuspect pond water and sediment samples supported the hypothesis that these samples were capable of inducing these abnormalities as the result of either the presence of developmental toxicants or the absence of essential micronutrients. Physicochemical characterization of the causes of abnormal frog embryo-larval and limb development were performed using the frog embryo teratogenesis assay-Xenopus (FETAX). Specific compounds were subsequently identified within the complex mixture fractions and tested by dilution in a control solution and native reference water using both the 4- and 30-d treatment protocols. Results from these studies suggested that a complex mixture of both naturally occurring and man-made compounds was primarily responsible for the effects observed in X. laevis. The potency of several compounds wasalso enhanced by the site water, thus indicating that the water matrix deserves consideration as a contributing factor for both laboratory and field studies. [ABSTRACT FROM AUTHOR]

Presents news briefs relating to biology. Production of a pharmaceutically valuable human protein in mouse milk, which is considered the first step in creating sheep, goats, or cows which can inexpensively create therapeutic proteins; Addition of the regulatory segment of a mouse milk-protein gene to the human gene for TPA, an anticlotting agent which can treat heart attacks or clotting disorders; Discovery that mucus on the skin of the African clawed frog contains certain peptides and indoleamines, known as neuromodulators, which cause predatory snakes to yawn, and that the frog may be useful in pharmacological studies designed to uncover how these chemicals affect the chemistry of the human brain and address disorders such as Parkinson's disease; Field-tests of the ability of a genetically modified form of Pseudomonas syringae bacteria to reduce frost damage to potatoes at the University of California at Berkeley.