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PubMed1998

Antimicrobial peptides from amphibian skin: what do they tell us?

Amphibian skin secretions contain many biologically active compounds, such as biogenic amines, complex alkaloids, or peptides. Within the latter class of molecules, a large number of peptide antibiotics has been isolated and characterized from different amphibian species. Antimicrobial peptides are considered the effector molecules of innate immunity, acting as a first line of defense against bacterial infections, by perturbing the phospholipid bilayer of the target cell membrane. These gene-encoded molecules are synthesized as inactive precursors and in several cases their proparts were shown to have highly conserved structures. It has also been demonstrated that the promoter regions of inducible peptide antibiotics are often regulated by the transcriptional control machinery NF-kappa B/I kappa B alpha. In amphibia of Rana and Bombina genera, inhibition of transcription of the genes encoding antimicrobial peptides has been obtained by glucocorticoid treatment, which causes an increase of I kappa B alpha synthesis. Moreover, determination of the structure of a number of genes coding for antimicrobial peptides in amphibia has actually shown that their promoter regions contain recognition sites for nuclear factors.

Amino Acid Sequence↗
PubMed2000

Retinal stem cells in vertebrates.

In fish and amphibia, retinal stem cells located in the periphery of the retina, the ciliary marginal zone (CMZ), produce new neurons in the retina throughout life. In these species, the retina grows to keep pace with the enlarging body. When birds or mammals reach adult proportions, however, their retinas stop growing so there appears to be no need for such a proliferative area with stem cells. It is a surprise, therefore, that recent data suggest that a region similar to the CMZ of fish and amphibia exists in the postnatal chick and the adult mouse.

Animals↗
PubMed1981

Biological role of the pars intermedia in lower vertebrates.

The most obvious function of the pars intermedia in lower vertebrates is the secretion of melanocyte-stimulating hormone (MSH) for the purpose of pigmentary control. In some amphibia, elasmobranchs and teleosts, the histological study of the pars intermedia, the radioimmunoassay of pituitary and plasma MSH and the effects of hypophysectomy and of MSH injection suggest that the activity of the pars intermedia is regulated to satisfy the needs of cryptic colour change. MSH secretion is associated with dispersion of melanin granules and with melanogenesis. However, in other teleost species, both the evidence from pituitary cytology and the failure to respond to MSH injection suggest that pigmentary change is not regulated by changes in the plasma titres of MSH. Results discussed here indicate that MSH alone may be inadequate for pigmentary control. Evidence for non-pigmentary functions of the pars intermedia is circumstantial and fragmentary. It is based on cytological observations of altered pars intermedia activity under certain conditions, and on observations of physiological changes that accompany increased melanotropic activity. Such function include effects of plasmas titres of cortisol in teleosts, resistance to adrenaline-induced hyperglycaemia in toads, and effects on neural activity in fish and amphibia. Evidence for pars intermedia involvement in osmoregulation is briefly discussed.

Amphibians↗
PubMed1985

Glial fibrillary acidic (GFA) protein in vertebrates: immunofluorescence and immunoblotting study with monoclonal and polyclonal antibodies.

We report a comparative immunofluorescence and immunoblotting study of GFA protein, the subunit of glial filaments, in nonmammalian vertebrates. The study was conducted with polyclonal antibodies raised to human and shark antigen and with monoclonal antibodies isolated from mice immunized with chicken and bovine antigen. With the exception of cyclostomes, glial filaments appeared remarkably conserved in vertebrate phylogeny, both with respect to the molecular weight and immunoreactivity of their protein subunit. In most species, the antibodies decorated a single band in brain, spinal cord, and optic nerve extracts by the immunoblotting procedure. This band had the same molecular weight in the different CNS regions. With the exception of the turtle, species differences in the molecular weight of the band were not greater than those observed among mammalian vertebrates (human, bovine, and rat). However, there were some exceptional findings in fish. In goldfish and trout brain and spinal cord extracts, the antibodies decorated with the same intensity two bands. In accordance with previous immunofluorescence findings, goldfish optic nerve extracts were negative by the immunoblotting procedure. In four fishes (sea bass, tautog, trout, and scup), optic nerves reacted with the antibodies. However, the band decorated by the antibodies was higher in molecular weight than that obtained from brain and spinal cord extracts. Glial fibers were demonstrated by immunofluorescence in the brain, spinal cord, optic nerve, and retina of most species studied. In amphibia immunofluorescent structures were comparatively few, probably accounting for the negative results by immunoblotting. A comparative immunohistological study of the cerebellum showed the presence of perpendicular glial fibers in the molecular layer of most species examined. Birds and amphibia were different in this respect. Bergmann glia in chicken were GFA negative. In the frog and the toad, immunofluorescent fibers in the molecular layer of the cerebellum were haphazardly oriented. Ependymal radial glia was GFA-negative in the cerebellum of subavian vertebrates. Antisera raised in rabbit to shark GFA protein reacted with the same bovine GFA fragments recognized by polyclonal and monoclonal antibodies raised to human and bovine antigens, respectively, i.e., 30-kDa N-bromosuccinimide fragment (tryptophan cleavage); 35-kDa 2-nitro-5-thiocyanobenzoic acid fragment (cysteine cleavage); 18-kDa cyanogen bromide fragment (methionine cleavage). Conversely, the chicken GFA monoclonal antibodies selected for this study only reacted with noncleaved protein.

Animals↗
PubMed1993

Scotopic spectral sensitivity of the optomotor response in the green treefrog Hyla cinerea.

Amphibians are unusual among vertebrates in having two spectral classes of rod photoreceptors, unique amphibian "green" rods and typical vertebrate "red" rods. Although amphibians have been the subject of extensive research on visual function, it is not known whether possession of two classes of rods is a general feature of Amphibia, nor is it clear to what behaviors each class of rods contributes. The Hylidae comprise one of the largest families within Amphibia but have been little studied with respect to visual function. Here, we demonstrate the presence of green and red rods in Hyla cinerea by microspectrophotometry and provide evidence for the contribution of green rods to one visually based behavior, the optomotor response. In addition, we discuss the role of green and red rods in visually based behavior in light of apparently conflicting demands resulting from the need to maximize absolute sensitivity, visual acuity, and color sensitivity.

Animals↗
PubMed1997

Primary structure of insulin from the african lungfish, Protopterus annectens.

Among the extant Sarcopterygii, the interrelationship between the Dipnoi (lungfishes), Actinistia (coelacanths), and Tetrapoda (tetrapods) is controversial. Insulin has been purified from an extract of the pancreas of the African lungfish Protopterus annectens and its primary structure established as A-chain, Gly-Ile-Val-Glu-Gln-Cys-Cys-His-Lys-Pro10-Cys-Ser-Leu- Tyr -Glu-Leu-Glu-Asn-Tyr-Cys20-Asn-Val-Pro; and B-chain, Ala-Val-Leu-Asn-Gln-His-Leu-Cys-Gly-Ser10-His-Leu-Val- Glu- Ala-Leu-Tyr-Leu-Val-Cys20-Ala-Asp-Asn-Gly-Phe- Phe-Tyr-Lys-Pro-Ser30-Gly. Lungfish insulin contains unusual structural features, such as the dipeptide extension to the C-terminus of the A-chain and the substitution Arg --> Asn at position B-23 in the putative receptor binding region of insulin, which may be expected to influence appreciably its biological potency relative to mammalian insulins. Lungfish insulin also contains amino acid substitutions such as Gly --> Ala at position B-21, Glu --> Asp at position B-22, and a Lys --> Ser residue at position B-30, previously found in insulins from amphibia. This observation is consistent with paleontological data suggesting that lungfish and amphibia share a close phylogenetic relationship.

Amino Acid Sequence↗
PubMed1983

Calcite in the statoconia of amphibians: a detailed analysis in the frog Rana esculenta.

The otoconia of Amphibia, especially of the frog Rana esculenta, were studied by X-ray diffraction and scanning electron microscopy (SEM). The SEM studies showed that the membranous labyrinth of Amphibia contains two populations of crystals, which can easily be distinguished by their forms. The X-ray diffraction data indicated that these two populations consist of calcite and aragonite; the endolymphatic sac, the saccule and the lagena contain aragonite, whereas calcite is only found in the otolithic membrane of the utricle. The genetic and functional significance of the existence of two crystalline forms of calcium carbonate in the membranous labyrinth are discussed.

Animals↗
PubMed1988

Hepatic alpha 1 and beta adrenergic receptors in various animal species.

Plasma membranes were isolated from the livers of various animal species representing the four vertebrate classes: Amphibia, Reptilia, Aves and Mammalia. These liver plasma membranes displayed comparable levels of purity as judged by marker enzyme analysis. The activities of the two marker enzymes, 5'-nucleotidase and gamma-glutamyltranspeptidase displayed striking, and quite different, species-dependent differences, with no apparent relationship to phylogeny. alpha 1 and beta-adrenergic receptors were characterized in isolated liver plasma membranes by radioligand binding techniques. The hepatic beta-adrenergic receptor was found to be expressed in all animals studied; the hepatic alpha 1-adrenergic receptor was absent in Amphibia and Reptilia, co-expressed with the beta receptor in Aves, and dominant over the beta receptor in Mammalia. These results suggest that, in liver, the beta-adrenergic receptor is more primitive while the alpha 1-adrenergic receptor is of a more recent phylogenetic origin. It is proposed that the latter may have evolved in conjunction with hepatic sympathetic innervation.

Animals↗
PubMed1986

Histamine in endocrine cells in the stomach. A survey of several species using a panel of histamine antibodies.

Antibodies to histamine were used to examine the localization of the amine in cells of the stomach and upper small intestine of a great variety of species, including cartilaginous and bony fish, amphibia, reptiles (lizard), birds (chicken) and a large number of mammals. In all species gastric histamine was localized in endocrine cells (invariably found in the epithelium) and mast cells (usually with an extra-epithelial localization). The endocrine cells were identified as such by immunostaining with antibodies to chromogranin A and the mast cells were identified by toluidine blue staining. Histamine-immunoreactive endocrine cells were found almost exclusively in the acid-producing part of the stomach; only rarely were such cells observed in the pyloric gland area. They were fairly numerous in the gastric mucosa of the two subclasses of fish as well as in the amphibia and reptile species studied. Here, the majority of the histamine-immunoreactive endocrine cells seemed to have contact with the gastric lumen (open type cells) and were located in the surface epithelium (certain fish only) or together with mucous neck cells at the bottom of the pits. In the chicken, histamine-immunoreactive endocrine cells were numerous and located peripherally in the deep compound glands. They were without contact with the lumen (closed type) and had long basal extensions ("paracrine" appearance), running close to the base of the oxyntic-peptic cells. In mammals, the number of histamine-immunoreactive endocrine cells in the stomach varied greatly. They were particularly numerous in the rat and notably few in the dog, monkey and man. In all mammals, the histamine-immunoreactive endocrine cells were of the closed type and located basally in the oxyntic glands. They often had a "paracrine" appearance with long basal processes. Histamine-storing mast cells, finally, were few in both subclasses of fish as well as in the amphibian species and in the lizard. They were fairly numerous in chicken proventriculus (beneath the surface epithelium), few in the oxyntic mucosa of mouse, rat and hamster, moderate in number in hedgehog, guinea-pig, rabbit, pig and monkey, and numerous in cat, dog and man.(ABSTRACT TRUNCATED AT 400 WORDS)

APUD Cells↗
PubMed1989

Histochemistry of glycoconjugates in the gallbladder epithelium of ten animal species.

A battery of seven lectins and several conventional mucin histochemical techniques were used to identify the epithelial mucins of the gallbladder of ten species: man, rabbit (Oryctolagus cuniculus, mammalia), hamster (Mesocricetus auratus, mammalia), chicken (Gallus gallus, bird), sparrow (Passer domesticus, bird), moorish gecko (Tarentola mauritanica, reptilia), ladder snake (Elaphe scalaris, reptilia), lake frog (Rana perezi, amphibia), natterjack toad (Bufo calamita, amphibia) and gilthead sea bream (Sparus auratus, fish). Glycogen was found in the epithelial lining of the reptilian and amphibian gallbladders. Sulphate and carboxyl groups were frequently found in the same species, except in the ladder snake and natterjack toad gallbladders where only sulphate groups were identified. Sialic acid residues were detected in man, rabbit, bird, T. mauritanica, R. perezi and fish gallbladders. ConA binding pattern was similar in the ten species studied. In the human gallbladder only PNA failed to label the luminal surface, while the glands were only unreactive to DBA. The human gallbladder showed a large variety of saccharides. The present results suggest that no relation exists between the composition of the gallbladder mucins and the situation of the species in the phylogenetic scale.

Animals↗
PubMed1993

Heterochronical patterns of evolution in the transitional stages of vertebrate classes.

Transitional forms of the recent classes of vertebrates are only known in paleontology. The well described examples are: Eusthenopteron foordi (Crossopterygii), Ichthyostega and Acanthostega (Labyrinthodontia) between Osteichthyes and Amphibia, Seymouria baylorensis (Amphibiosaria) between Amphibia and Reptilia, Archaeopteryx lithographica (Archaeornithes) between Reptilia and Aves, and the mammal-like reptiles Pelycosauria, Therapsida and Cynodontia between Reptilia and Aves, and the description of their phylogenetical heterochronies in terms of peramorphosis and paedomorphosis shows the progressive role of the motorial, especially the locomotorial organ systems and their functions in comparison with the retarded evolution of the axial system, especially the skull and central nervous system. The evolution of the Hominidae shows the same rule. The evaluation of these transitional forms in their fossil context reveals them as inhabitants of biotopes situated in the border areas of coastal and shore landscapes of marine, brackish or fresh water. These biotopes have obviously favoured the innovations on the high taxonimic level of macro-evolutionary characteristics.

Animals↗
PubMed1981

Structural organization of nascent transcripts and hnRNA molecules in amphibian oocytes.

Comparisons of relative lengths of lampbrush loops, nascent RNP transcripts and hnRNA molecules from oocytes of amphibia with different C-values show that there is an increasing trend in loop, and transcriptional unit, length with increase in genome size but no increasing trend with respect to RNA contour length. The formation of duplex regions and circles in RNP fibrils indicates that RNA processing may occur within the nascent fibrils. The hnRNA molecules from oocytes of the various amphibia readily form intermolecular duplex structures. These complementary sequences have a low kinetic complexity and are transcribed from highly repetitive sequences distributed throughout the genome. Their possible function is considered.

Animals↗
PubMed1985

Studies on the attachment response of Isthmiophora melis cercariae (Trematoda: Echinostomatidae).

The cercaria of Isthmiophora melis is relatively specific to suitable intermediate hosts, amphibia and fish, as early as the stage of attachment. Attachment responses are maximally stimulated by intact amphibia, whereas isolated frog tissues have a reduced efficiency. Human urine contains attachment triggering substances. Its effectiveness is reduced, when carbonate systems are removed, and may be restored by addition of carbonate. Aqueous solution systems of dissolved CO2 and H2CO3/HCO-3 stimulate attachment responses, especially at pH 6.0-7.5. The attachment response to frog skin surface seems to be triggered by the buffering system, which uses carbonate solution equilibria as important components.

Amino Acids↗
PubMed1979

Reversible inhibition by lanthanum of the hydrosmotic response to serosal hypertonicity in toad urinary bladder.

In the urinary bladder of amphibia, hypertonicity of the serosal bath (SH) evokes an increase in transepithelial water permeability, the characteristics of which resemble the response to antidiuretic hormone (ADH). The ionic dependency, in particular for Ca2+, appears very similar for SH- and ADH-induced water fluxes. In the present experiments La3+ was used as a probe to study the Ca2+-dependency of the hydrosmotic response to SH in isolated urinary bladder of the toad Bufo marinus. Addition of La3+ (5 mM) on the serosal side of the membrane produced a significant and reversible increase in basal transepithelial water flux. The hydrosmotic response elicited by adding 250 mM mannitol to the serosal Ringer's solution was inhibited by 30% in the absence of serosal Ca2+. Similarly, the hydrosmotic response to SH was inhibited by 37%, 30% and 40% when 5 mM La3+ was added to the serosal medium 30 min before, concommitantly with, or 60 min after induction of SH. The inhibition of transepithelial water flux observed in the absence of serosal Ca2+ or in the presence of serosal La3+ was reversible. The results support a critical role for Ca2+ in the modulation of transepithelial water permeability in the urinary bladder of amphibia. Ca2+ presumably exerts its effects at a post-cyclic AMP step.

Animals↗
PubMed1982

Tuberculosis in wildlife in the Ruwenzori National Park, Uganda (Part II).

The results of post-mortem examinations of 90 warthog (Phacochoerus aethiopicus) conducted in the Ruwenzori National Park, Uganda during a survey of tuberculous infection in wildlife are described. Nine per cent of warthog were found to show gross lesions on autopsy and of these organisms which could by typed, Mycobacterium bovis was isolated in 2 of 6 cases and 5 atypical mycobacterial strains were isolated from the remaining 4. The distribution and character of the lesions is described and it is concluded that the route of infection in the warthog is alimentary. A mycobacterial survey of 8 other species of mammals, 7 species of birds, 5 species of fish and 1 species of amphibian is described. None of the mammals (except possibly 1 elephant), birds, fish or amphibia is described. None of the mammals (except possibly 1 elephant), birds, fish or amphibia was found to be infected with M. bovis but several individuals were found to harbour atypical, probably saprophytic, mycobacterial types. The origin of tuberculosis in buffalo and warthog in the Ruwenzori National Park is discussed and is concluded to have been previous contact with domestic cattle.

Amphibians↗
PubMed1983

In vitro study of frog (Rana ridibunda Pallas) neurointermediate lobe secretion by use of a simplified perifusion system. II. Lack of action of thyroxine on TRH-induced alpha-MSH secretion.

Thyrotropin-releasing hormone (TRH) stimulates alpha-melanocyte-stimulating hormone (alpha-MSH) secretion in amphibia as well as thyrotropin-stimulating hormone (TSH) and prolactin secretions in mammals. Since thyroid hormones regulate the stimulatory effect of TRH on TSH and prolactin, the possible role of thyroxine (T4) in the control of alpha-MSH secretion in amphibia, has been investigated. Neurointermediate lobes of Rana ridibunda were perifused in amphibian culture medium for 7 hr and the amounts of alpha-MSH released into the effluent perfusate were measured by radioimmunoassay. In vivo treatment with T4 (0.5 mg/kg twice a day for 9 days) did not modify the in vitro response of the neurointermediate lobes to TRH (10(-9) to 10(-7) M). In addition, prolonged infusion of T4 in vitro did not alter spontaneous and TRH-induced alpha-MSH release. In spite of the inhibitory effect of T4 on TRH-induced TSH and prolactin secretions in mammals, the present data show that, in frogs, thyroid hormone does not modulate the stimulation of alpha-MSH secretion induced by TSH.

Animals↗
PubMed1992

Thyroid hormone receptors and iodothyronine deiodinases in the developing Mexican axolotl, Ambystoma mexicanum.

The Mexican axolotl, Ambystoma mexicanum, is a neotenous salamander that rarely undergoes anatomical metamorphosis, but can be induced to do so by administration of thyroxine (T4). The neoteny appears to be due primarily to low levels of plasma T4 secondary to a low rate of secretion of thyroid-stimulating hormone. However, other factors may also be involved. In anuran amphibia, metamorphosis is accompanied by alterations in thyroid hormone receptor concentration and marked changes in the activities of the iodothyronine deiodinase systems, all of which contribute to enhancing peripheral sensitivity to circulating T4. The present study was designed to assess these functions in the tissues of the axolotl. Putative 3,5,3'-triiodothyronine (T3) receptors were readily detected in axolotl red blood cells, and the receptor number (sites/nucleus) showed a developmental decline, comparable to that seen in anuran amphibia, as the larval cells with a high receptor number were replaced with adult cells with a low receptor number. Saturable T3 nuclear binding sites were also detected in liver, but the receptor number was too low to quantitate. Using a sensitive RIA, T4 and T3 were below detectable levels in juvenile axolotls and T4 was just detectable in some of the adults. Following injection of [125I]T4, [125I]T3 was detected in plasma and liver of adult, but not of juvenile, axolotls. Some 5'-deiodinase activity was consistently detected in preparations of larval skin, and in adult skin and gut, but it was too low to permit kinetic analyses. Activity was not increased following treatment with sufficient T4 to induce anatomical metamorphosis. 5-Deiodinase activity was not detected in any tissue.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1985

Amino acid sequence microheterogeneities of basic (type II) cytokeratins of Xenopus laevis epidermis and evolutionary conservativity of helical and non-helical domains.

Three clones coding for carboxy-terminal portions of type II cytokeratins have been isolated from a cDNA library constructed from the epidermis of the frog Xenopus laevis. These clones have been identified by hybridization-selection-translation and Northern blot analysis, and contain sequences complementary to mRNAs of similar size that code for three different polypeptides of the Mr 64,000 group, Ia-c, i.e. the only major type II cytokeratins expressed in this tissue. A comparison of the corresponding nucleotide sequences and the amino acid sequences deduced therefrom shows only minor differences in these polypeptides, most of which occur as isolated point mutations. This indicates that coding sequences of the different type II cytokeratin genes in epidermis of Xenopus are very similar, in contrast to the more extended differences of type II cytokeratin genes expressed in mammalian epidermis, which probably reflects a lower degree of evolutionary divergence of members of this protein family in amphibia. A comparison of the Xenopus sequences with those of mammalian type II cytokeratins reveals the same characteristic features, i.e. an alpha-helical domain ending with the familiar consensus sequence T Y R (X Y) L E G E, followed by a non-helical domain Cl enriched in hydroxyamino acids. Both domains are remarkably conserved in sequence between Xenopus and mammals. The following glycine-rich domain (C2) displays similar oligopeptide repeats (mostly of the type G G G M in the frog keratins), and the terminal C3 domain is characterized by a region exceptionally rich in hydroxyamino acids, which immediately precedes a cluster of basic amino acids at the carboxy terminus. Our results show that the typical features of the domain of type II cytokeratins are already established in amphibia and that these homologies are not restricted to the alpha-helical rod of these proteins but, in principle, extend to the other domains located in the so-called hypervariable tail portion. This suggests that the hypervariable regions are not subject to random variability but contain functionally important domains that have been well conserved during evolution.

Amino Acid Sequence↗