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PubMed2000

Characterization of insulin and atypically processed proglucagon-derived peptides from the surinam toad Pipa pipa (Anura:Pipidae).

Electrospray mass spectrometry was used to identify insulin, glucagon and two peptides related to glucagon-like peptide-1 (GLP-1) in an extract of the pancreas of the Surinam toad, Pipa pipa, a species belonging to the same family as the African clawed frog, Xenopus laevis. Purification and characterization of the peptides established the primary structure of Pipa insulin as A-chain: GIVEQCCHSS(10)CTLLQLETYC(20) N and B-Chain: FSNQR LCGSH(10) LVEALHLVCG(20) DRGFFYYPKA(30). This amino acid sequence contains several substitutions (B5 His --> Arg, B16 Tyr --> His, A12 Ser --> Thr, A14 Tyr--> Leu, A18Asn --> Thr) of residues that have otherwise been quite strongly conserved during vertebrate evolution. Pipa glucagon comprises 37 amino acid residues (HSQGTFTSDY(10) SKYLDSRRAQ(20) DFVQWLMNTK(30)QSGGLSS) and the 29 amino-acid-residue peptide was not identified in the extract. In Xenopus and mammalian preproglucagons, the glucagon-29 sequence is followed by Lys-Arg which functions as a recognition site for a prohormone convertase. We propose that a point mutation in the gene encoding Pipa preproglucagon has transformed the Lys(30)-Arg(31) processing site into Lys-Gln with the result that the site in no longer recognized by the processing enzyme. In contrast, Pipa GLP-32 and GLP-37 are of the same molecular size as the corresponding peptides from Xenopus.

Amino Acid Sequence↗
PubMed1988

Morphology of the caudal spinal cord in Rana (Ranidae) and Xenopus (Pipidae) tadpoles.

Using a variety of neuroanatomical and histological techniques, we compare the spinal cord and peripheral nerve distribution in the tails of larvae from Xenopus laevis and three species of Rana. The relatively large, postsacral spinal cord of Xenopus contains abundant motoneurons and their axons. Spinal nerves exit from the spinal cord in a regular array, one nerve per myotome, from the cervical region to near the end of the tail. Somata of motoneurons innervating caudal myotomes are found along the entire length of the tail. In contrast, the caudal cord of Rana is reduced to a filum terminale consisting of little more than an ependymal tube; spinal nerves to all caudal myotomes leave the cord in the sacral region and reach their motor targets via a cauda equina and caudal plexus. Motoneuron cell bodies innervating caudal myotomes are found only in the sacral region. The Rana larval pattern is similar to that of adult frogs and mammals, whereas the Xenopus larval pattern is more like that of salamanders and reptiles. These gross neuroanatomical differences are not due to differences in the size or developmental stage of the tadpoles, but instead are associated with differences in the swimming behavior of the larvae. The presence of motoneurons in the caudal spinal cord of Xenopus may provide local intermyotomal control within the tail; the elongated topography of the cord appears to permit finer, rostral-to-caudal regulation of neuromuscular activity. The Rana spinal cord, on the other hand--with motoneurons clustered anteriorly--may produce concurrent firing of adjacent ipsilateral myotomes, but at the expense of fine intermyotomal regulation. The fact that nerves in the tail of Xenopus enter and exit from the spinal cord locally, as opposed to far anteriorly as in Rana, means that for tadpoles of the same size, reflex arc lengths are many times shorter in Xenopus.

Animals↗
PubMed1977

The free swimming Pipa larvae, with a review of pipid larvae and pipid phylogeny (Anura: Pipidae).

This paper describes the morphology of the free swimming Pipa larvae, compares them with Xenopus, Hymenochirus, and to some extent, Rhinophrynus larvae, and presents a morphological diagnosis of pipid larvae. Pipa and Xenopus have very similar chondrocrania. Hymenochirus is superficially different but has the same diagnostic features. The differences appear related to its small size and predatory habitus. Other aspects of anatomy, especially the filter apparatus are very different in each genus. The filter apparatus of Pipa is somewhat reduced and seems modified for the retention of relatively large (20+ microns) particles. Similar adaptations may have been annectant to predations in Hymenochirus, which lacks a filter apparatus. However, varying states of seven character complexes, which cut across the varying ecology, show that there are two basic pipid lineages, each currently confined to Africa or South America, respectively. Recent finds of fossil South American Xenopus indicate that these two lineages separated before the continents did. This does not warrant the recognition of two subfamilies because Xenopus and Hymenochirus are too different. Pseudhymenochirus is not an intermediate between them; it is primitive Hymenochirus. Eight character states separate pipid and rhynophrynid larvae.

Animals↗
PubMed1992

Glomerular development and growth of the renal blood vascular system in Xenopus laevis (Amphibia: Anura: Pipidae) during metamorphic climax.

Microcorrosion casts of the renal vascular system of tadpoles of the Clawed Frog, Xenopus laevis, were observed by scanning electron microscopy. Glomerular differentiation was studied qualitatively and quantitatively during developmental stages 56-66 (metamorphic climax). The general structure of the renal vascular system corresponds to the pattern commonly found in anurans; however, the arterial supply has conspicuous connecting vessels that supply groups of glomeruli. In the dorsal part of the kidney, qualitative differentiation of glomerular structures precedes quantitative growth. The ventral part of the kidney has larger, well-developed renal corpuscles of nearly adult appearance. Four developmental stages of glomerulogenesis are distinguished morphologically and their glomerular and vascular growth is analyzed.

Animals↗
PubMed1992

Skeletal development in Xenopus laevis (Anura: Pipidae).

Postembryonic skeletal development of the pipid frog Xenopus laevis is described from cleared-and-stained whole-mount specimens and sectioned material representing Nieuwkoop and Faber developmental Stages 46-65, plus postmetamorphic individuals up to 6 months old. An assessment of variation of skeletogenesis within a single population of larvae and comparison with earlier studies revealed that the timing, but not the sequence, of skeletal development in X. laevis is more variable than previously reported and poorly correlated with the development of external morphology. Examination of chondrocranial development indicates that the rostral cartilages of X. laevis are homologous with the suprarostral cartilages of non-pipoid anurans, and suggests that the peculiar chondrocranium of this taxon is derived from a more generalized pattern typical of non-pipoid frogs. Derived features of skeletal development not previously reported for X. laevis include 1) bipartite formation of the palatoquadrate; 2) precocious formation of the adult mandible; 3) origin of the angulosplenial from two centers of ossification; 4) complete erosion of the orbital cartilage during the later stages of metamorphosis; 5) development of the sphenethmoid as a membrane, rather than an endochondral bone; and 6) a pattern of timing of ossification that more closely coincides with that of the pelobatid frog Spea than that recorded for neobatrachian species.

Animals↗
PubMed1987

Chromosome banding in amphibia. XI. Constitutive heterochromatin, nucleolus organizers, 18S + 28S and 5S ribosomal RNA genes in Ascaphidae, Pipidae, Discoglossidae and Pelobatidae.

The karyotypes of 14 species of Anura from 9 genera of the suborders Amphicoela, Aglossa, Opisthocoela and Anomocoela were analysed with various banding techniques and conventional cytogenetic methods. The 18S + 28S and 5S ribosomal RNA genes were localized by means of in situ hybridization. No Q-, R- and G-banding patterns in the euchromatic segments of the metaphase chromosomes could be demonstrated in any of the species; this does not seem to be caused by a higher degree of spiralization of the amphibian chromosomes, but by the special DNA organization in these organisms. In most karyotypes, constitutive heterochromatin is present at centromeres, telomeres and nucleolus organizer regions (NORs), but rarely in interstitial positions. The heterochromatic regions are either quinacrine positive and mithramycin negative or vice versa. All species examined possess only one homologous pair of NORs: these display the brightest mithramycin fluorescence in the karyotypes. Many specimens exhibited unequal labelling of the two NORs both after silver and mithramycin staining as well as after in situ hybridization with 3H-18S + 28S rRNA. In four species, between one and six chromosome pairs with homologous 5S rRNA sites could be identified. The 5S rRNA genes and the 18S + 28S rRNA genes are closely linked in two species. In the male meiosis of the Amphicoela and Opisthocoela, there are intersitial, subterminal and terminal chiasmata in the bivalents, whereas only terminal chiasmata are observed in the bivalents of the Aglossa and Anomocoela. No heteromorphic sex-specific chromosomes could be demonstrated in any of the species. The differential staining techniques revealed that the chromosomal structure in these four suborders is largely the same as in the highly evolved anuran suborders Procoela and Diplasiocoela.

Amphibians↗
PubMed2001

Antimicrobial peptides isolated from skin secretions of the diploid frog, Xenopus tropicalis (Pipidae).

Seven peptides (XT-1-XT-7) with antimicrobial activity were isolated from norepinephrine-stimulated skin secretions of the diploid clawed frog, Xenopus tropicalis. Structural characterization of the peptides demonstrated that amino acid sequence similarity to antimicrobial peptides previously isolated from Xenopus laevis was low, suggesting that the species are not closely related phylogenetically. Peptides XT-5 and XT-3 are probably the orthologs of X. laevis peptide glycine-leucine amide (PGL(a)) and the N-terminal spacer region of prolevitide, respectively. XT-1, XT-6 and XT-7 show limited structural similarity to the spacer region of X. laevis procaeruleins and the paralogs XT-2 and XT-4 are similar to corresponding regions of proxenopsin. Orthologs of the magainins were not identified. The C-terminally alpha-amidated peptide XT-7 (GLLGPLLKIAAKVGSNLL.NH2) showed the lowest minimum inhibitory concentrations against reference microorganisms (Staphylococcus aureus 5 microM, Escherichia coli 5 microM, and Candida albicans 40 microM) and was also active against clinical isolates of methicillin-resistant S. aureus, Staphylococcus epidermidis, Staphylococcus saprophyticus, Streptococcus group C, Shigella sonnei, Pseudomonas aeruginosa and Enterobacter cloacae. The peptide was, however, hemolytic against human erythrocytes (50% lysis at 70 microM). Circular dichroism studies showed that XT-7 has a random structure in aqueous solution, pH 7.0 but adopts an alpha-helical conformation in the presence of 50% trifluoroethanol. Decreasing the cationicity of XT-7 either by replacement of the C-terminal CONH2 group by COOH or by deletion of the Lys(8) residue produced analogs with greatly (>10-fold) decreased antimicrobial potencies.

Amino Acid Sequence↗
PubMed2001

Anomalous rates of evolution of pancreatic polypeptide and peptide tyrosine-tyrosine (PYY) in a tetraploid frog, Xenopus laevis (Anura:Pipidae).

The South African clawed frog Xenopus laevis is believed to have arisen as a result of a tetraploidization event occurring approximately 30 million years ago. Two molecular forms of pancreatic polypeptide (PP) have been isolated from an extract of the pancreas of this species and two molecular forms of peptide tyrosine-tyrosine (PYY) from the intestine. Despite the fact that the amino acid sequence of PP has, in general, been very poorly conserved during the evolution of tetrapods (only Pro(5), Pro(8), Gly(9), Ala(12), Tyr(27), Arg(33) and Arg(35) are invariant among species studied so far), the two Xenopus PPs differ by only a single amino acid substition (Asp(22)-->Glu). In contrast the two molecular forms of PYY differ by six amino acid substitutions (Glu(15)-->Gln, Thr(18)-->Ala, Leu(21)-->Met, Ile(22)-->Thr, Ile(28)-->Val, Val(31)-->Ile). The data imply that strong evolutionary pressure is acting to conserve the functional domain in both genes encoding PP and so suggest that PP may have an important physiological role in amphibians (although the nature of this role has yet to be determined). The more rapid mutation of the functional domain in the genes encoding PYY, a peptide whose amino acid sequence has been quite well conserved in tetrapods and whose physiological significance is well established, suggests that one of the PYY genes may be evolving towards a new function or towards becoming a pseudogene.

Amino Acid Sequence↗
PubMed1985

Evolution of globin expression in the genus Xenopus (Anura: Pipidae).

Comparison of electrophoretic globin phenotypes of 18 different Xenopus taxa reveals four different basic types of banding patterns. Each type includes species that also are similar in their morphological, cytogenetical, and biochemical characteristics. Three of these patterns reflect distinct evolutionary lines, while the fourth may be interpreted as the intersection of two of these lines. The composition of the basic pattern of the highly polyploid species is consistent with an allopolyploid origin of most of these species. The number of distinct globin polypeptides--four in the only extant diploid species, X. tropicalis, and five or more in most of the tetraploid species, including X. laevis--suggests that primordial globin genes had undergone duplication either before or after the tetraploidization event. Finally, the individual globin phenotypes are excellent molecular markers that are of great help in identifying the various species but not the subspecies.

Animals↗
PubMed1980

Uptake of Tc-99m-PIPIDA in pulmonary metastases from a hepatoma.

Metastatic pulmonary nodules from a well-differentiated hepatoma were well demonstrated by a Tc-99m-labeled hepatobiliary imaging agent. Uptake of this type of radionuclide by metastases from a primary hepatic malignancy has not previously been reported. Such radiopharmaceuticals may prove useful in the future as imaging agents for primary hepatobiliary tumors.

Adult↗
PubMed1982

Fortuitous findings of Tc-99m PIPIDA hepatobiliary scintigraphy.

Hepatobiliary scintigraphy using Tc-99m labeled radiopharmaceuticals is employed primarily for the diagnosis of acute cholecystitis and for demonstration of biliary tract potency. This produce may also provide diagnostic information in the identification of unusual or atypical hepatobiliary disorders; frequently, this occurs as an incidental result of the test. We present five cases in which trauma, infection, or obstructive abnormalities were diagnosed fortuitously.

Adolescent↗
PubMed1983

Imaging patterns with 99mTc-PIPIDA in evaluating abdominal pain.

A random retrospective review of hepatobiliary scans on 86 adult patients with abdominal pain revealed four distinct imaging patterns: normal, cystic duct obstruction, obstructive, and sick liver pattern. A normal pattern was found to exclude acute cholecystitis and was the pattern most frequently observed.

Abdomen↗
PubMed1977

The karyotype of the tetraploid species Xenopus vestitus Laurent (Anura: pipidae).

Xenopus vestitus possesses 72 chromosomes, wherease in the majority of known Xenopus species there are 2n = 36. During meiosis, 36 bivalents are usually observed at metaphase I and 36 chromosomes at metaphase II. Arranged according to size and centromere position, the chromosomes form the same basic morphologic groups typical of the genus Xenopus. However, the groups are composed of quartets of four similar chromosomes instead of diploid pairs of homologs. The exception to this arrangement involves chromosomes bearing secondary constrictions, which in X. vestitus are represented by two different pairs of homologs, one of which shows, in 39% of the observed mitoses, somatic association and is, therefore, considered to carry the nucleolar organizer. X. vestitus represents either a case of ancient autotetraploidy or, more likely, one of allotetraploidy of more modern origin.

Animals↗
PubMed1980

The karyotype of the hexaploid species Xenopus ruwenzoriensis Fischberg and Kobel (Anura: Pipidae).

The chromosome number of the hexaploid species Xenopus ruwenzoriensis is 108. The chromosomes fall into sets of six usually similar chromosomes (hextets) which can be classified into the morphological groups characteristic for the genus Xenopus. However, the three distinct secondary constrictions, typical for X. ruwenzoriensis, appear on two homologs only within a particular hextet, unmasking an underlying heterogeneity. The secondary constrictions on chromosome pair 11 show chromosomal association and are considered to represent the nucleolar organizer regions. There is no evidence of dimorphic sex chromosomes. Plates of spermatocyte metaphase I generally show bivalents, but single large multivalents have also been observed. In the majority of cases, 54 dyads are found in second spermatocyte metaphases. X. ruwenzoriensis is, therefore, either an ancient autohexaploid or, more likely, an allopolyploid of more recent origin.

Animals↗