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At least 19 recordsLinked to original sources
PubMed1976

Studies on immunoglobulins of Xenopus borealis, Xenopus clivii and Xenopus muelleri.

Following immunization with human IgG three species of anuran amphibians, Xenopus borealis, Xenopus clivii and Xenopus muelleri, were found to synthesize two molecular populations of antibodies associated with 19S and 7S fractions of the sera. These antibodies, designated high (HMW) and low (LMW) molecular weight immunoglobulins, were isolated and their constituent heavy (H) and light (L) polypeptide chains separated following extensive reduction and alkylation in a relative yield of about 70% and 30% respectively. The molecular weights of H and L chains of the three species were determined by SDS-acrylamide gel electrophoresis. The L chains from both molecules in the three species had a molecular weight of about 26,000. The H chains of the HMW and LMW immunoglobulins had a molecular weight of about 73,000 and 63,000 respectively. The two populations of immunoglobulins were analysed in immunodiffusion plates using rabbit antisera to LMW immunoglobulins. The HMW immunoglobulins were found to be antigenically deficient with respect to LMW immunoglobulins. From these results it was judged that the two populations in each species belonged to distinct classes. The antigenicities of the LMW and HMW immunoglobulins of different species within the genus Xenopus were compared.

Animals↗
PubMed1979

Contrasting denaturation maps of Xenopus laevis and Xenopus borealis mitochondrial DNAs.

Denaturation maps of mitochondrial DNAs of Xenopus laevis and Xenopus borealis are radically different from each other. This is in striking contrast to the invariant denaturation patterns previously recognized among mtDNAs of various Drosophila species, particularly, since the two toads may be even more closely related to each other than the Drosophila species.

Animals↗
PubMed1978

The nucleotide sequences of 5.8-S ribosomal RNA from Xenopus laevis and Xenopus borealis.

1. The nucleotide sequence of 5.8-S rRNA from Xenopus laevis is given; it differs by a C in equilibrium U transition at position 140 from the 5.8-S rRNA of Xenopus borealis. 2. The sequence contains two completely modified and two partially modified residues. 3. Three different 5' nucleotides are found: pU-C-G (0.4) pC-G (0.2) and pG (0.4). 4. The 3' terminus is C not U as in all other 5.8-S sequences so far determined. 5. The X. laevis sequence differs from the mammalian and turtle sequences by five and six residue changes respectively. 6. A ribonuclease-resistant hairpin loop is a principle feature of secondary structure models proposed for this molecule. 7. Sequence heterogeneity may occur at one position at a very low level (approximately 0.01) in X. laevis 5.8-S rRNA, while none was detected in X. borealis or HeLa cell 5.8-S rRNA.

Animals↗
PubMed1977

[Effects of alpha-amanitin on the development of Xenopus (Xenopus laevis Daud.) heart in vitro].

The differentiation of Xenopus heart is studied in vitro, in the presence of alpha-amanitin. The results obtained depend on the concentration of the inhibitor, the length of treatment and the stage of primordium. The mRNA pool assures the differentiation of explants, removed from young stages, for 12 hours. This time is half for the primordia removed from stages greater than 3,5 mm.

Amanitins↗
PubMed1978

A biochemical comparison of Xenopus laevis and mammalian myelin from the central and peripheral nervous systems.

Myelin purified from the central nervous system of Xenopus laevis contained the same major lipid and protein components as human myelin. However, some minor differences in the myelin proteins were noted. The Xenopus basic protein had a higher apparent mol wt. on sodium dodecyl sulfate gels than the corresponding mammalian protein. The absolute specific activity of 2',3'-cyclic nucleotide 3'-phosphohydrolase in the Xenopus myelin was considerably higher than in mammals. There were differences in the high mol wt. proteins, and the glycoproteins in Xenopus myelin were more heterogeneous than those in mammals. Peripheral myelin from Xenopus sciatic nerve was compared with that from the rat. The lipids in the two types of myelin were similar. There was a major glycoprotein in the Xenopus myelin corresponding to the P0 protein and a basic protein of slightly larger mol wt. than the P1 protein of rat myelin.

2',3'-Cyclic-Nucleotide Phosphodiesterases↗
PubMed1978

A natural heterohaemagglutinin in Xenopus laevis serum.

In most adult Xenopus laevis the serum contains a 'natural' factor capable of lysing the erythrocytes from a wide variety of amniote species. The factor has no effect on the erythrocytes of another amphibian, Ambystoma mexicanum, nor will serum from one animal lyse red cells from another Xenopus individual. No lysing factor was present in the serum of larval (tadpole) Xenopus. Heating of Xenopus serum to 56 degrees for 30 min, absorption of the serum with zymosan or inulin, or removal of calcium and magnesium ions results in loss of lytic activity, although haemagglutinating activity remains, suggesting that the factor can fix complement. The factor elutes from a gel chromatography column in the 19S peak, and is inactivated by thiol reduction and subsequent alkylation. These findings, coupled with immunoabsorption studies suggest that the haemagglutinin is an immunoglobulin of the IgM class. The significance of this suggestion is discussed in the light of previous reports of 'natural' heterohaemagglutinins in other species.

Agglutinins↗
PubMed1979

In vitro synthesis of RNA by Xenopus spermatogenic cells I. Evidence for polyadenylated and non-polyadenylated RNA synthesis in different cell populations.

Premeiotic and postmeiotic (haploid) gene expression during spermatogenesis in the anuran, Xenopus laevis, was studied by analyzing the accumulation of radioactively labelled cytoplasmic polyadenylated [poly (A +)] and non-polyadenylated [poly (A -)] RNAs. Dissociated spermatogenic cells were labelled and maintained in an in vitro system capable of supporting cell differentiation. Labelled cells were separated by density gradient centrifugation into subpopulations enriched for individual spermatogenic stages. RNA was extracted and purified from each cell fraction, and separated into poly (A +) and poly (A -) species. Comparison of poly (A +) to non-poly (A) radioactivity in cells labelled with tritiated uridine or adenosine demonstrated that (1) all cell fractions produced significant quantities of polyadenylated RNA relative to total RNA synthesis; and (2) that a cell fraction enriched for pachytene spermatocyte RNA contained up to 15% of total cytoplasmic and 35% of total polysomal RNA labelled as poly (A +) containing species. RNA was also characterized by sucrose density gradient centrifugation and polyacrylamide gel electrophoresis. All cell types showed typical poly (A -) peaks of 4S, 18S and 28S, corresponding to tRNA (4S) and rRNAs (18, 28S) respectively. Spermatids and spermatozoa had additional absorbance peaks at 13 and 21S which cosedimented with Xenopus oocyte mitochondrial rRNA. Patterns of incorporation of uridine and adenosine into poly (A +) RNA in all germ cell fractions tested were complex. In all cases, major areas of radioactivity were found in a broad band sedimenting between 6-17S. Spermatid fractions showed a prominent peak of incorporation at 6-8S, while pachytene cells also showed heavier poly (A +) peaks in the 17-25S region. A non-polyadenylated RNA species sedimenting at 6-8S with a relatively rapid rate of turnover was also observed in spermatids. From these results it is concluded that synthesis of transfer, ribosomal, and putative messenger RNA species continues in spermatogenic cells throughout all but the very last stages of spermatogenesis in Xenopus.

Animals↗
PubMed1979

Structure and formation of ankylosis in Xenopus laevis.

The structure of ankylotic teeth in Xenopus laevis was studied by light, transmission, and scanning electron microscopy as well as by microradiography in decalcified and undecalcified specimens. The mature teeth of Xenopus laevis are calcified from the crown to the base, fused to the jaw bone, and have no uncalcified area, such as a fibrous ring separating the tooth into the crown and pedicle. Microradiography shows that the mature tooth and jaw bone appear as an X-ray opaque area, except for the basal region of the dentine. This region is composed of an X-ray translucent area and an X-ray opaque thin layer on the lingual side of the translucent area. The mature tooth is composed of two differently calcified areas: (1) a highly calcified area, which makes up almost all of the tooth and contains a thin layer of the basal dentine on the lingual side, and (2) a lowly calcified basal dentine, which is fused to the jaw bone. Therefore, the lowly calcified area does not completely separate the dentine and jaw bone. Repeating banding patterns among the collagen fibrils differ among the dentine-forming area and the matrices of dentine and jaw bone. During the formation of ankylosis of the tooth germ, collagen bundles in the dentine-forming area accumulate directly on the surface of the jaw bone. Consequently, the mature teeth of Xenopus laevis fuse to the jaw bone directly without the mediation of the other structures.

Animals↗
PubMed1975

Innervation of the male genital tract and kidney in the amphibia, Xenopus laevis Daudin, Rana temporaria L., and Bufo bufo L.

The innervation of the male genital tract and kidney in three anuran species was studied by the fluorescence histochemical method of Falck-Hillarp for the demonstration of monoamines whose identity was secured by thin-layer chromatography, and by electron microscopy including administration of 5- or 6- hydroxydopamine (5- and 6-ODHA). The genital tract comprises testis, intra- and extratesticular and intrarenal seminal efferent ducts, Bidder's canal, renal dorsal transverse ducts, and ureter. In addition--depending on the species studied--renal corpuscles and the various portions of uriniferous tubules may be involved in sperm transport. 1. Adrenaline is the main transmitter in nerves supplying the male genital tract and kidney. Only in Xenopus is it possible to demonstrate the presence of noradrenaline, which was confirmed in the chromatographic analysis. No obvious changes are observed with regard to the distribution, amount, and fluorescence intensity of adrenergic fibers and their susceptibility towards 5- and 6-OHDA when comparing animals killed in late autumn and winter, or in late spring, respectively. Non-adrenergic nerve fibers have not been observed. 2. The adrenergic innervation in the testis is only scarce and confined to blood vessels. Neuro-endocrine contacts on Leydig cells are not established. The gonadal ducts and the specific (i.e. non-vascular) are intratesticular smooth muscle cells in Xenopus are not innervated. 3. Apart from the uriniferous tubules (see below), only the ureter receives an adrenergic innervation which, however, is scarce even around the time of spermiation. Bundles of non-terminal and terminal axons are seen running contiguous to the superficial bundles of smooth muscle or smooth muscle-like cells. Neuromuscular relationships comprise synapses at distances of 2000-5--- A, but no close contacts. In the seminal vesicle of Rana the same mode of apposition of adrenergic terminals to muscle cells is observed. In addition, a direct innervation of the epithelium is seen in a few instances. 4. In the kidney the renal arteries, afferent arterioles, and the main branches of the kidney the renal arteries, afferent arterioles, and the main branches of the portal veins are supplied by a dense plexus of adrenergic nerves. Small groups of intensely fluorescent cells are found in the walls of the renal portal veins and veins proper. The density of the arteriolar plexus is more pronounced in Rana and Bufo than in Xenopus. In Rana and Bufo the arteriolar innervation comprises terminals at "ordinary" smooth musculature with membrane-to-membrane appositions, as well as contacts at a distance of 800 to 4000 A on juxtaglomerular epitheloid cells...

Animals↗
PubMed1978

Frequency response of the lateral-line organ of Xenopus laevis.

The stimulus response relation of the epidermal lateral-line organ of Xenopus laevis was studied by recording activity of single afferent nerve fibres in isolated preparations. Linear frequency response analysis over a frequency range of 0.1--100Hz was performed under steady-state conditions, using small amplitude, sinusoidal water displacements produced by a glass sphere at a short distance from the skin. Period histograms of afferent nerve activity were computed, and amplitude, phase and mean activity of the response were determined by means of Fourier analysis. A standardization procedure at the start of each experiment made scaling of the frequency responses of different preparations unnecessary. The results show that for small stimulus amplitudes the response of the lateral-line organ over the whole range of frequencies studied can adequately be described as a modulation of the spontaneous activity. The amplitude of the response is proportional to the stimulus amplitude, and the phase of the response is independent of stimulus amplitude. The lateral-line organ of Xenopus laevis can thus be regarded as a linear system for stimuli which produce modulation of the spontaneous activity. The frequency response demonstrates unequivocally that the lateral-line organ of Xenopus laevis functions as a water velocity detector. For frequencies of stimulation from 0.1--20Hz the gain increases with a slope of 7.5 dB/oct, and up to 5Hz the response is almost in phase with the water velocity. The extent to which the different transmission steps between stimulus and response will contribute to the frequency response is discussed.

Animals↗
PubMed1979

Aerobic and anaerobic contributions to sustained activity in Xenopus laevis.

In conditions of declining water PO2, Xenopus obtains the majority of resting oxygen needs from lung breathing at 15 degrees and 25 degrees C. The critical oxygen tension was 120 +/- 9 mm Hg at 15 degrees C, and 90 +/- 10 mm Hg at 25 degrees C. During 30 min stimulation of activity to complete exhaustion at 15 degrees C, frogs exhibited an aerobic capacity of 1.7 microliter O2.g-1.h-1 and accumulated 2.22 mg lactate . g-1. Following activity these animals exhibited an oxygen debt of 49.2 microliter O2.g-1. At 25 degrees C, Xenopus had an aerobic capacity of 16.1 microliter O2.g-1 and accumulated 1.94 mg lactate . g-1. Following activity, 25 degrees C frogs exhibited an oxygen debt of 261.9 microliter O2.g-1. Thus at 15 degrees C, Xenopus acquires 85% of the ATP used during a bout of sustained exhaustive activity from anaerobic sources, and 98% at 25 degrees C. Recovery from exhaustive activity was complete after 5 h at 25 degrees C and 9 h at 15 degrees C. Comparison of these data with those of other amphibians stimulated to sustained activity suggests that aquatic amphibians can tolerate a larger lactate load than can terrestrial forms.

Animals↗
PubMed1978

Oestrogen-induced cholesterol and fatty acid biosynthesis in Xenopus laevis liver during vitellogenic response.

1. Oestradiol-17beta induces livers of Xenopus laevis (South African clawed toad) to synthesize and secrete into the serum large quantities of the egg-yolk-protein precursor, vitellogenin. The peak of this response occurs 9-16 days after hormone treatment [Dolphin, Ansari, Lazier, Munday & Akhtar (1971) Biochem. J.124, 751-758]. It is now shown that 6 days after hormone treatment a 120-160-fold stimulation of the synthesis of cholesterol and fatty acid compared with control values occurred. 2. A cell-free system, derived from Xenopus liver, which synthesizes squalene and fatty acid is described. By using this system, several hundredfold stimulation of incorporation of [(14)C]acetate into squalene was recorded 6 days after the administration of oestradiol-17beta, compared with a 3-4-fold stimulation of incorporation of [(3)H]mevalonate compared with control values. It is argued that oestradiol-17beta must affect enzyme(s) catalysing step(s) between acetate and mevalonate in the biosynthetic pathway to cholesterol. 3. In incubation of liver slices in vitro, most of the lipid and cholesterol synthesized in response to the steroid hormone was associated with those subcellular fractions that contained membranes. Moreover, pulse-labelling experiments in vivo showed that 70% of this lipid and cholesterol was retained in the liver. The remainder appeared in the serum, where it was equally distributed between vitellogenin and vitellogenin-free serum. 4. G.l.c. analyses of the cholesterol content of liver microsomal fractions of Xenopus laevis indicated that the cholesterol content was at least 50% higher in microsomal fractions obtained from livers that had been exposed to oestradiol-17beta. Meanwhile, g.l.c. analysis of the lipid moiety of secreted vitellogenin showed that up to 35% of its lipid was cholesterol.

Animals↗
PubMed1977

Prescence of tadpole and adult globin RNA sequences in oocytes of Xenopus laevis.

Complementary DNA transcribed from adult Xenopus laevis globin mRNA was used to assay ovary RNA from Xenopus for the presence of globin sequences by RNA.cDNA hybridization. These sequences are present at approximately the same concentration as the majority of poly(A)-containing ovary sequences. The sequences are also found at approximately 200,000 copies per cell in poly(A)-containing RNA extracted from mature oocytes. To rule out contamination of the oocytes with somatic cells, two additional experiments were performed. First, RNA isolated from ovulated unfertilized eggs, which are devoid of somatic cells, was also shown to contain the globin sequences. Second, globin mRNA was isolated from Xenopus tadpoles. Adult globin mRNA is free of the tadpole sequence and no homology was detected between adult and tadpoles globin RNA. The ovary was shown to contain tadpole globin RNA at nearly the same concentration as the adult sequences. Thus, the results cannot be explained by contamination with erythroid cells which should contain only the adult sequence. The swimming tadpole, which possesses an active circulatory system, was also assayed for the tadpole and adult globin sequences. Whereas the adult sequences are present at approximately the same concentration as in the mature oocyte, the concentration of the tadpole sequences increases at least 300-fold in the first 3 days following fertilization.

Animals↗
PubMed1978

Actin in Xenopus oocytes.

It has been found that a high-speed supernatant fraction from Xenopus oocytes extracted in the cold will form a clear, solid gel upon warming. Gel formation occurs within 60 min at 18 degrees-40 degrees C, and is, at least initially, temperature reversible. Gelation is strictly dependent upon the addition of sucrose to the extraction medium. When isolated in the presence of ATP, the gel consists principally of a 43,000-dalton protein which co-migrates with Xenopus skeletal muscle actin on SDS-polyacrylamide gels, and a prominent high molecular weight component of approx. 250,000 daltons. At least two minor components of intermediate molecular weight are also found associated with the gel in variable quantities. Actin has been identified as the major consituent of the gel by ultrastructural and immunological techniques, and comprises roughly 47% of protein in the complex. With time, the gel spontaneously contracts to form a small dense aggregate. Contraction requires ATP. In the absence of exogenous ATP, a polypeptide which co-migrates with the heavy chain of Xenopus skeletal muscle myosin becomes a prominent component of the gel. This polypeptide is virtually absent from gels which have contracted in ATP-containing extracts. It has also been found that Ca++ is required for gelation in oocyte extracts. At both low and high concentrations of Ca++ (defined as a ratio of Ca++/EGTA in the extraction medium), gelation is inhibited.

Actins↗
PubMed1978

Recombinant plasmids containing Xenopus laevis globin structural genes derived from complementary DNA.

Details are presented of the in vitro synthesis of double-stranded DNA complementary to purified Xenopus globin messenger RNA, using a combination of reverse transcriptase, fragment 'A' of E. coli DNA polymerase 1 and S1 endonuclease. After selection of duplex DNA molecules approaching the length of Xenopus globin messenger RNA by sedimentation of the DNA through neutral sucrose gradients, the 3'-OH termini of the synthetic globin gene sequences were extended with short tracts of oligo dGMP using terminal transferase. This material was integrated into oligo dCMP-extended linear pCR1 plasmid DNA and amplified by transfection of E. coli. Plasmids carrying globin sequences were identified by hybridization of 32P-labelled globin mRNA to total cellular DNA in situ, by hybridization of purified plasmids to globin cDNA in solution, by analysis of recombinant DNA on polyacrylamide and agarose gels, and by heteroduplex mapping. The results show that extensive DNA copies of Xenopus globin mRNA have been integrated into recombinant plasmids.

Animals↗