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PubMed2001

Slow ATP loss and the defense of ion homeostasis in the anoxic frog brain.

For most vertebrates, cutting off the oxygen supply to the brain results in a rapid (within minutes) loss of ATP, the failure of ATP-dependent ion-transport process, subsequent anoxic depolarization of neuronal membrane potential and consequential neuronal death. The few species that survive brain anoxia for days or months, such as the freshwater turtle Trachemys scripta, avoid anoxic depolarization and maintain brain ATP levels through a coordinated downregulation of brain energy demand processes. The frog Rana pipiens represents an intermediate in anoxia-tolerance, being able to survive brain anoxia for hours. However, the anoxic frog brain does not defend its energy stores. Instead, anoxia-tolerance appears to be related to a retarded rate of ATP depletion. To investigate the relationship between this slow ATP depletion and the loss of ionic homeostasis, cerebral extracellular K(+) concentrations were monitored and ATP levels measured during anoxia, during the initial phase of anoxic depolarization and during complete anoxic depolarization. Extracellular K(+) levels were maintained at normoxic levels for at least 3 h of anoxia, while ATP content decreased by 35 %. When ATP levels reached 0.33+/-0.06 mmol l(-1) (mean +/- S.E.M., N=5), extracellular K(+) levels slowly started to increase. This value is thought to represent a critical ATP concentration for the maintenance of ion homeostasis. When extracellular [K(+)] reached an inflection value of 4.77+/-0.84 mmol l(-1) (mean +/- S.E.M., N=5), approximately 1 h later, the brain quickly depolarized. Part of the reduction in ATP demand was attributable to an approximately 50 % decrease in the rate of K(+) efflux from the anoxic frog brain, which would also contribute to the retarded rate of increase in extracellular [K(+)] during the initial phase of anoxic depolarization. However, unlike the anoxia-tolerant turtle brain, adenosine did not appear to be involved in the downregulation of K(+) leakage in the frog brain. The increased anoxia-tolerance of the frog brain is thought to be a matter more of slow death than of enhanced protective mechanisms.

Adenosine Triphosphate↗
PubMed2002

Adaptive plasticity of skeletal muscle energetics in hibernating frogs: mitochondrial proton leak during metabolic depression.

The common frog (Rana temporaria) spends the coldest months of each year overwintering in ice-covered ponds where temperatures can vary from 0.5 to 4.0 degrees C. Over the course of a winter season, the animals enter progressively into a state of metabolic depression that relies almost exclusively on aerobic production of ATP. However, if aerobic metabolism is threatened, for example by increasingly hypoxic conditions, decreases in the animal's metabolic rate can reach upwards of 75% compared with the 50% decrease seen during normoxia. Under these conditions, the major proportion of the overall reduction in whole-animal metabolic rate can be accounted for by metabolic suppression of the skeletal muscle (which makes up approximately 40% of body mass). Little is known about the properties of mitochondria during prolonged periods of metabolic depression, so we have examined several aspects of mitochondrial metabolism in the skeletal muscle of frogs over periods of hibernation of up to 4 months. Mitochondria isolated from the skeletal muscle of frogs hibernating in hypoxic water show a considerable reorganisation of function compared with those isolated from normoxic submerged animals at the same temperature (3 degrees C). Both the active (state 3) and resting (state 4) respiration rates of mitochondria decrease during hypoxic, but not normoxic, hibernation. In addition, the affinity of mitochondria for oxygen increases during periods of acute hypoxic stress during normoxic hibernation as well as during long-term hibernation in hypoxic water. The decrease in mitochondrial state 4 respiration rates during hypoxic hibernation evidently occurs through a reduction in electron-transport chain activity, not through a lowered proton conductance of the mitochondrial inner membrane. The reduced aerobic capacity of frog skeletal muscle during hypoxic hibernation is accompanied by lowered activities of key enzymes of mitochondrial metabolism caused by changes in the intrinsic properties of the mitochondria. In the absence of oxygen, the mitochondrial F(1)F(o)-ATPase (the ATP synthase) begins to run backwards as it actively pumps protons from the matrix in an attempt to maintain the mitochondrial membrane potential. At this time, the ATP synthase functions as an ATPase to preserve a certain proton-motive force. Frogs limit ATP wastage during anoxia by a profound inhibition of the ATP synthase. Taken together, our studies show that protonmotive force is lowered aerobically by restricting electron supply and during anoxia by restricting mitochondrial ATPase activity.

Animals↗
PubMed2005

Effects of nonylphenol and triclosan on production of plasma vitellogenin and testosterone in male South African clawed frogs (Xenopus laevis).

We investigated the effects of nonylphenol (NP) and triclosan (TCS) on production of vitellogenin (Vg), testosterone (T), and hepatic cytochrome P450 1A and 2B activities in male South African clawed frogs (Xenopus laevis). In a 14-d waterborne exposure test, no significant differences in the level of plasma Vg synthesis in male frogs were observed among the control, 10, 50, and 100 microg/l NP and 20, 100, and 200 microg/l TCS treatment groups. Intraperitoneal injection of male frogs with 2, 20, and 200 microg/g body weight NP resulted in no significant differences in plasma Vg levels among the control and all treatment groups. However, the levels of plasma Vg in all TCS treatment groups (intraperitoneal injection of 4, 40, and 400 microg/g body weight) were lower than that in the solvent control group, and male frogs injected with high doses of NP or TCS had lower T levels than the control group. No significant differences in hepatic cytochrome P450 1A and 2B activities were observed among the all treatment groups. Male frogs injected with 20 microg/g body weight of estradiol-17beta had significantly higher plasma Vg levels than the control group. These results suggest that profiles of plasma Vg and T production in male Xenopus laevis could be useful biomarkers for detecting hormonally active agents.

Animals↗
PubMed1998

Evolutionary relationships among Japanese pond frogs inferred from mitochondrial DNA sequences of cytochrome b and 12S ribosomal RNA genes.

The evolutionary relationships among Japanese pond frogs (Rana nigromaculata, R.porosa porosa, and R. p. brevipoda) were investigated by analyzing nucleotide sequences of mitochondrial cytochrome b (cyt b) and 12S rRNA genes. The nucleotide sequences of 444-bp segment of the cyt b gene and 410-bp segment of 12S rRNA gene were determined by the PCR-direct sequencing method using 18 frogs from 13 populations of Japanese pond frogs, and phylogenetic trees were constructed by the neighbor-joining and maximum likelihood methods using R. catesbeiana as an outgroup. The sequenced 444-bp segment of cyt b gene provided 69 variables sites, and the sequenced 410-bp segment of 12S rRNA gene provided 21 variables sites. The numbers of nucleotide substitutions per site of the cyt b gene within ingroup were 0.0022-0.0205 at the populational level, 0.0368-0.0462 at the racial or subspecific level, and 0.1038-0.1244 at the specific level, whereas those of the 12S rRNA gene were 0-0.0074 at the populational or subspecific level, and 0.0378-0.0456 at the specific level. Most nucleotide substitutions within ingroup occurred at the third codon position of the cyt b gene and were silent mutations. High frequencies of transitions relative to transversions were shown at cyt b and 12S rRNA genes within ingroup. The phylogenetic trees constructed from the nucleotide sequences of the cyt b gene showed that after outgroup R. catesbeiana separated from ingroup frogs, ingroup Japanese pond frogs diverged into R.nigromaculata and R.porosa, then the latter diverged into R.p. porosa, R.p. brevipoda (the typical Okayama race), and the Nagoya race of R.p.porosa. The phylogenetic trees constructed from the nucleotide sequences of the 12S rRNA gene also showed distinct divergence between two species, but not any divergence within species.

Amino Acid Sequence↗
PubMed2000

Sequence variation and structural conservation in the D-loop region and flanking genes of mitochondrial DNA from Japanese pond frogs.

The nucleotide sequences of the D-loop region and its flanking genes of the mitochondrial DNA (mtDNA) from Japanese pond frogs were determined by the methods of PCR, cloning, and sequencing. The frogs belonged to two species, one subspecies, and one local race. The gene arrangements adjacent to the D-loop region were analyzed. The frogs shared a unique mitochondrial gene order that was found in Rana catesbeiana; i.e., cyt b--D-loop region--tRNA(Leu(CUN))--tRNA(Thr)--tRNA(Pro)--tRNA(Phe)--12S rRNA. The arrangements of the three tRNA genes of these frogs were different from those of X. laevis, a species which has the same overall structure as in mammals. Highly repetitive sequences with repeat units (16-bp or 17-bp sequence specific for each taxon) were found in the D-loop region. The length of repetitive sequences varied from 0.6 kbp to 1.2 kbp, and caused the extensive size variation in mtDNA. Several short sequence elements such as putative TAS, OH, CSB-1, and CSB-2 were found in the D-loop region of these frogs. The sequences of these short regulatory elements were conserved in R. catesbeiana, X. laevis, and also in human. The comparison of sequence divergences of the D-loop region and its adjacent genes among various taxa revealed that the rates of nucleotide substitutions depend on genes. The nucleotide sequences of the 3'-side segment of the D-loop region were the most variable among taxa, whereas those of the tRNA and 12S rRNA genes were the most conservative.

Animals↗
PubMed2005

Intersexuality and the cricket frog decline: historic and geographic trends.

Exposure to anthropogenic endocrine disruptors has been listed as one of several potential causes of amphibian declines in recent years. We examined gonads of 814 cricket frogs (Acris crepitans) collected in Illinois and deposited in museum collections to elucidate relationships between the decline of this species in Illinois and the spatial and temporal distribution of individuals with intersex gonads. Compared with the preorganochlorine era studied (1852-1929), the percentage of intersex cricket frogs increased during the period of industrial growth and initial uses of polychlorinated biphenyls (PCBs) (1930-1945), was highest during the greatest manufacture and use of p,p-dichlorodiphenyltrichloroethane (DDT) and PCBs (1946-1959), began declining with the increase in public concern and environmental regulations that reduced and then prevented sales of DDT in the United States (1960-1979), and continued to decline through the period of gradual reductions in environmental residues of organochlorine pesticides and PCBs in the midwestern United States (1980-2001). The proportion of intersex individuals among those frogs was highest in the heavily industrialized and urbanized northeastern portion of Illinois, intermediate in the intensively farmed central and northwestern areas, and lowest in the less intensively managed and ecologically more diverse southern part of the state. Records of deposits of cricket frog specimens into museum collections indicate a marked reduction in numbers from northeastern Illinois in recent decades. These findings are consistent with the hypothesis that endocrine disruption contributed to the decline of cricket frogs in Illinois.

Animals↗
PubMed1995

The need for water quality criteria for frogs.

Amphibians are considered reliable indicators of environmental quality. In the western United States, a general decline of frog populations parallels an apparent worldwide decline. The factors thought to be contributing to declines in frog populations include habitat loss, introduction of exotic species, overexploitation, disease, climate change, and decreasing water quality. With respect to water quality, agroecosystems use 80-90% of the water resources in the western United States, frequently resulting in highly eutrophic conditions. Recent investigations suggest that these eutrophic conditions (elevated pH, water temperature, and un-ionized ammonia) may be associated with frog embryo mortality or malformations. However, water quality criteria for frogs and other amphibians do not currently exist. Here, we briefly review data that support the need to develop water quality parameters for frogs in agroecosystems and other habitats.

Abnormalities, Drug-Induced↗
PubMed2003

Inhibition of the basal and oestradiol-stimulated mitotic activity of primary spermatogonia by melatonin in the testis of the frog, Rana esculenta, in vivo and in vitro.

Melatonin has a direct inhibitory effect on the basal and oestradiol-stimulated mitotic activity of primary spermatogonia in the testis of the frog, Rana esculenta. In this study oestradiol was used to induce spermatogonial proliferation to verify the anti-proliferative effect of melatonin. The colchicine metaphase arrest technique was used. The results obtained from in vivo experiments confirm that oestradiol increases the mitotic index of primary spermatogonia and, for the first time, indicate that melatonin has an inhibitory role on the proliferation of primary spermatogonia in the frog testis. Similar results were obtained from testes of melatonin-injected frogs that were exposed to oestradiol in vitro; in fact spermatogonia were unresponsive to hormonal stimulation. In addition, in short-term cultured testes, melatonin (at physiological concentration) interferes with the effects of oestradiol on spermatogonial proliferation, supporting the hypothesis that melatonin exerts the inhibitory effect directly via its local action on the frog gonads. Morphological observation after in vivo or in vitro melatonin treatments indicates that Leydig cells display degenerative features, whereas in adjacent germinal tubules, Sertoli cells show heterochromatic nuclei. These results indicate that melatonin may act on Leydig cells and confirm that there is a paracrine interaction between interstitial and germinal compartments. The results of the present study indicate, for the first time, that melatonin may be directly involved in the inhibitory control of spermatogonial proliferation in the testis of the frog, R. esculenta.

Animals↗
PubMed2005

Determining sexual dimorphism in frog measurement data: integration of statistical significance, measurement error, effect size and biological significance.

Several analytic techniques have been used to determine sexual dimorphism in vertebrate morphological measurement data with no emergent consensus on which technique is superior. A further confounding problem for frog data is the existence of considerable measurement error. To determine dimorphism, we examine a single hypothesis (Ho = equal means) for two groups (females and males). We demonstrate that frog measurement data meet assumptions for clearly defined statistical hypothesis testing with statistical linear models rather than those of exploratory multivariate techniques such as principal components, correlation or correspondence analysis. In order to distinguish biological from statistical significance of hypotheses, we propose a new protocol that incorporates measurement error and effect size. Measurement error is evaluated with a novel measurement error index. Effect size, widely used in the behavioral sciences and in meta-analysis studies in biology, proves to be the most useful single metric to evaluate whether statistically significant results are biologically meaningful. Definitions for a range of small, medium, and large effect sizes specifically for frog measurement data are provided. Examples with measurement data for species of the frog genus Leptodactylus are presented. The new protocol is recommended not only to evaluate sexual dimorphism for frog data but for any animal measurement data for which the measurement error index and observed or a priori effect sizes can be calculated.

Analysis of Variance↗
PubMed2003

Helminth community structure of sympatric eastern American toad, Bufo americanus americanus, northern leopard frog, Rana pipiens, and blue-spotted salamander, Ambystoma laterale, from southeastern Wisconsin.

One-hundred twelve amphibians, including 51 blue-spotted salamanders, Ambystoma laterale, 30 eastern American toads, Bufo americanus americanus, and 31 northern leopard frogs, Rana pipiens, were collected during April-October 1996 from Waukesha County, Wisconsin and examined for helminth parasites. The helminth compound community of this amphibian assemblage consisted of at least 10 species: 9 in American toads, 8 in leopard frogs, and 3 in blue-spotted salamanders. American toads shared 7 species with leopard frogs, and 2 species occurred in all 3 host species. Although there was a high degree of helminth species overlap among these sympatric amphibians, statistically significant differences were found among host species and percent of indirect or direct-life cycle parasites of amphibian species individual component communities (chi2 = 1,015, P < 0.001). American toads had a higher relative abundance of nematodes, 59%, than larval cestodes, 31%, and larval and adult trematodes, 10%, whereas leopard frogs had a higher relative abundance of larval cestodes, 71.3%, and larval and adult trematodes, 25.3%, than nematodes 3.4%. This is related to ecological differences in habitat and dietary preferences between these 2 anuran species. Helminth communities of blue-spotted salamanders were depauperate and were dominated by larval trematodes, 94%, and few nematodes, 6%. Low helminth species richness in this host species is related to this salamander's relatively small host body size, smaller gape size, lower vagility, and more fossorial habitat preference than the other 2 anuran species. Adult leopard frogs and toads had significantly higher mean helminth species richness than metamorphs, but there was no significant difference in mean helminth species richness among adult and metamorph blue-spotted salamanders. Considering adult helminths, the low species richness and low vagility of caudatans as compared with anurans suggest that local factors may be more important in structuring caudatan helminth communities of salamanders than of anuran hosts. Helminth species infecting salamanders may be more clumped in their geographic distribution as compared with anurans, and the role of other hosts and their parasites at the compound community level may be important in structuring helminth communities of salamanders.

Ambystoma↗
PubMed2001

Structural and functional identification of the pituitary adenylate cyclase-activating polypeptide receptor VPAC2 from the frog Rana tigrina rugulosa.

Recently, a frog pituitary adenylate cyclase-activating polypeptide (PACAP)/vasoactive intestinal peptide (VIP) receptor (fPVR) has been characterized, and interestingly, this receptor exhibits characteristics of both mammalian PACAP type II receptors VPAC(1)R and VPAC(2)R. In order to investigate the receptors responsible for mediating the actions of VIP and PACAP in amphibians, in this report, a frog VPAC(2) receptor (fVPAC(2)R) cDNA was isolated. fVPAC(2)R shares 47.7, 46.9 and 62.5% amino acid sequence identity with fPVR, human VPAC(1)R and human VPAC(2)R respectively. Functionally, fVPAC(2)R, when expressed in CHO cells, was responsive to both frog peptides including VIP, PACAP38 and PACAP27 where the EC(50) values of these peptides in intracellular cAMP production were 0.15, 0.18 and 0.16 microM respectively. The pharmacological profiles of human peptides (VIP, PACAP38 and peptide histidine methionine) to stimulate frog and human VPAC(2)Rs were compared, and it was found that these peptides could only activate the frog receptor at micromolar concentrations. fVPAC(2)R was found to be widely distributed in various peripheral tissues as well as several regions of the brain. The presence of the receptor transcripts suggests the functional roles of the receptor in mediating the actions of PACAP and/or VIP in these tissues. As VIP and particularly PACAP27 are highly conserved peptides in vertebrate evolution, comparative studies of these peptides and their receptors in non-mammalian vertebrates should provide clues to better understand the physiology of these important peptides in human and other vertebrates.

Amino Acid Sequence↗
PubMed1993

Localization, characterization and activity of pituitary adenylate cyclase-activating polypeptide in the frog adrenal gland.

Pituitary adenylate cyclase-activating polypeptide (PACAP) has recently been isolated from the frog brain and the sequence of the peptide appears to be strikingly similar to that of mammalian PACAP. In the present study, we have investigated the localization of PACAP in the frog interrenal (adrenal) gland by immunocytochemistry using antisera directed against PACAP 38 or PACAP 27. Two types of PACAP-immunoreactive fibres were observed: thick varicose fibres coursing between adrenal cells and thin processes located in the walls of blood vessels irrigating the gland. Bilateral transection of the splanchnic nerves did not affect the intensity and distribution of PACAP immunoreactivity. The mean +/- S.E.M. concentration of PACAP, measured by radioimmunoassay in crude adrenal extracts, was 0.65 +/- 0.16 nmol/g wet tissue. Two molecular forms of PACAP in the adrenal gland were characterized by reversed phase high-performance liquid chromatography combined with radioimmunoassay quantification. The elution profiles revealed the existence of two peaks exhibiting the same retention times as synthetic frog PACAP 38 (fPACAP 38) and PACAP 27, the predominant form being PACAP 38. The possible involvement of PACAP in the regulation of adrenal steroidogenesis was investigated in vitro using a perifusion system for frog adrenal slices. Graded doses of fPACAP 38 (0.1-10 mumol/l) increased the secretion of both corticosterone and aldosterone in a dose-dependent manner. Administration of repeated pulses of fPACAP 38 (1 mumol/l), at 120-min intervals, led to a reproducible stimulation of corticosteroid secretion without any tachyphylaxis. Prolonged infusion (2 h) of the peptide induced a rapid increase in corticosterone and aldosterone output, followed by a gradual decline in the secretion rate, suggesting the occurrence of a desensitization phenomenon. Synthetic porcine vasoactive intestinal peptide, which is structurally related to PACAP, was about ten times less potent than fPACAP 38 in stimulating steroidogenesis while the [Des-His1]-fPACAP 38 analogue was 100 times less effective. These results demonstrate that a peptide closely related to fPACAP 38 is present in fibres innervating the frog adrenal gland and could participate in the regulation of corticosteroid secretion, particularly during neurogenic stress.

Adrenal Glands↗
PubMed1990

Histochemical demonstration of NADPH-diaphorase activity in the pineal organ of the frog (Rana esculenta), but not in the pineal organ of the rat.

Using the histochemical method for the demonstration of NADPH-diaphorase activity, the pineal organ of the frog and rat was investigated in serial sections. A positive NADPH-diaphorase activity was demonstrated in pinealocytes and nerve cells in the pineal organ of the frog, but not in the rat. An intense activity existed in the apical portion of the photosensitive pinealocytes of the frog. Large NADPH-diaphorase positive nerve cells (15-20 microns in diameter) were located within the parenchyma of the pineal organ in the frog. Large NADPH-positive nerve cells were more numerous in the rostral than in the caudal portion of the organ, but the intensely stained cells, counting 25-35 in number, showed almost equal distribution and number in the ventral and the dorsal aspect of the pineal organ. In their staining ability, NADPH-diaphorase positive pineal nerve cells resembled retinal amacrine cells. The results in the pineal organ of the frog are discussed in light of previous morphological findings using the acetylcholinesterase reaction, and with electrophysiological results.

Animals↗
PubMed2005

Ontogenic delays in effects of nitrite exposure on tiger salamanders (Ambystoma tigrinum tigrinum) and wood frogs (Rana sylvatica).

Under certain conditions, nitrite can be present in freshwater systems in quantities that are toxic to the fauna. I exposed wood frog (Rana sylvatica) and eastern tiger salamander (Ambystoma tigrinum tigrinum) embryos and young tadpoles and larvae to elevated concentrations of nitrite in chronic toxicity tests: 0, 0.3, 0.6, 1.2, 2.1, 4.6, and 6.1 mg/L NO2-N, exposing individuals as both embryos and larvae. Nitrite caused significant declines in wood frog hatching success (3.4 mg/L NO2-N, wood frog), and lower concentrations caused significant mortality during the early larval stages (4.6 mg/L NO2-N, salamander; 0.5 mg/L NO2-N, wood frog). Later tests exposing individuals to nitrite only after hatching showed that both wood frog and tiger salamander vulnerability to nitrite declined shortly after hatching. Hence, examining a single life-history stage, especially later in development, may miss critical toxic effects on organisms, causing the researcher potentially to underestimate seriously the ecological consequences of nitrite exposure.

Ambystoma↗
PubMed1975

Action site of antagonists of vitamin B6 in the central nervous system of the frogs and cockroaches.

Susceptibility to some antagonists of vitamin B6 was studied in frogs and cockroaches after operational intervention in their central nervous systems, and also in the intack frogs and cockroaches. Thiosemicarbazide, semicarbazide, isoniazide and penicillamine induced wild jumping behavior, and tonic or clonic convulsions in frogs, when the nervous parts posterior to the optic lobe inclusive remained intact. In frog, in which the nervous parts anterior to the diencephalon inclusive had been removed, no convulsions were induced by castrix or 4-deoxypyridoxine in large doses. In cockroaches excessive fluttering of wings and convulsions upon administration of thiosemicarbazide following severance of the central nerve cord between the subesophageal and prothoracic ganglions were induced. Castrix was not a convulsant in the intact frogs and cockroaches.

Animals↗
PubMed2006

The effect of serotonin on epinephrine modulation of transepithelial ion transport in isolated frog skin.

The aim of this study was to examine the effect of serotonin and epinephrine on ion transport of isolated frog skin. The addition of serotonin after incubation in Ringer solution (RH), bumetanide (BUME), and after initial incubation in amiloride and subsequently in RH, reduced hyperpolarization and did not effect the mechanosensitivity of frog skin. Following incubation of the frog skin with amiloride (AMI), serotonin did not affect the value of hyperpolarization and increased mechanosensitivity. The addition of epinephrine (EPI) on frog skin incubated in RH and AMI did not affect hyperpolarization, but repeated application of this compound after serotonin increased hyperpolarization. After incubation with bumetanide, addition of EPI before and after application of serotonin did not affect the value of the examined parameters of the frog skin. Initial incubation with AMI and later in RH caused a drop in reaction to EPI and no effect on mechanosensitivity. Repeated addition of epinephrine in this group did not affect the reaction value, while it decreased the reaction value during mechanical stimulation. The experimental data presented in this study indicate that serotonin inhibits the sodium ion current. Epinephrine inhibits the chloride ion current, however, after the application of serotonin, EPI stimulates sodium ion transport.

Animals↗
PubMed2002

Chytridiomycosis in native Arizona frogs.

Twenty-seven adult/sub-adult lowland leopard frogs (Rana yavapaiensis), two larval lowland leopard frogs, two adult Chirichahua leopard frogs (Rana chiricahuensis), and two adult canyon tree frogs (Hyla arenicolor) collected from populations experiencing mortality events at eight sites were found to have characteristic lesions of chytrid fungus infection (Batrachochytrium dendrobatidis). The mortalities occurred during December 1992 and between October and February in 1997-98 and December and February in 1998-99. Gross lesions varied from none to diffuse reddening of the skin of the abdomen, pelvic area, and legs. Microscopic lesions were characteristic of those previously reported for the disease and included diffuse epidermal hyperplasia, hyperkeratosis, and colonization of the keratinized layers of the epidermis by sporangia of the chytrid. Bacterial cultures did not yield a primary pathogenic agent. Virus isolation from frog tissues was negative. Batrachochytrium dendrobatidis was isolated from the skin of two of 10 R. yavapaiensis and one of two H. arenicolor cultured following necropsy. An additional nine of 11 clinically affected or dead R. yavapaiensis from the same locations, but not necropsied, were culture positive for B. dendrobatidis.

Animals↗
PubMed1999

Molecular cloning, characterization of cDNA, and distribution of mRNA encoding the frog prohormone convertase PC1.

Prohormone convertases (PCs) are calcium-dependent serine endoproteases of the subtilisin/kexin family that play a key role in the posttranslational processing of precursors for biologically active peptides. In this study, we have characterized the cDNA encoding PC1 in the European green frog Rana ridibunda. A frog brain cDNA library was screened by using a heterologous probe at low stringency, and a 2.3-kb cDNA clone encoding PC1 was isolated. This cDNA encodes a 736-residue protein with a 26-amino-acid signal peptide. Comparative structural analysis revealed that frog PC1 exhibits a high degree of amino acid identity with its mammalian counterparts, in particular in the subtilisin-like catalytic domain. Northern blot analysis resolved two major transcripts of 3.0 kb and 5.0 kb that were expressed differentially in the brain and pituitary. In situ hybridization studies showed that, in the frog brain, the highest densities of PC1 mRNA are present in the amygdala, the hypothalamus, and the anterior preoptic area. High concentrations of PC1 mRNA also were found in the pars distalis and pars intermedia of the pituitary, whereas the pars nervosa was devoid of hybridization signal. The wide distribution of PC1 mRNA in the brain and pituitary suggests that, in frog, PC1 is involved in the processing of a number of hormone and neuropeptide precursors.

Amino Acid Sequence↗