Development and ciliation of the palate in two frogs, Bombina and Xenopus; a comparative study

The morphological changes that occur during metamorphosis in the palates of two types of anuran larvae (a discoglossid, Bombina orientalis, and a pipid, Xenopus laevis) are compared. In B. orientalis the structural changes are accompanied by the ciliation of the palate epithelium. Ciliation begins in the anterior region of the palate and continues in a posterior direction throughout metamorphosis. By contrast, the palate of X. laevis never becomes ciliated during its development. Instead, two ciliated grooves develop between the choanae (nasal openings) and the esophageal opening. The grooves transport mucus and trapped objects out of the internal nares and toward the esophagus. These grooves are compared to similar structures on the palate of adult B. orientalis. The timing and pattern of ciliogenesis during metamorphosis in each of these anurans is also described relative to well-established staging series for external frog development. We show that the onset and location of ciliogenesis are consistent and predictable in these anurans and, therefore, make the frog palate an excellent system for the study of ciliogenesis.

In vitro induction of Xenopus oocyte maturation by 4-pregnene-17 alpha, 20 beta-diol-3-one

Maturation in Xenopus oocyte is initiated by progesterone and other steroids. The possibility that a metabolite of progesterone is the active agent was explored. In the present study the 20 beta-dihydro metabolite of progesterone, 4-pregnene-17 alpha, 20 beta-diol-3-one was found to be as potent as progesterone at concentrations of 0.5 to 3.0 microM in inducing germinal vesicle breakdown (GVBD) in Xenopus oocytes. The order of relative potencies of the steroids tested were progesterone approximately equal to 17 alpha-hydroxy-20 beta-dihydroprogesterone greater than 17 alpha-hydroxy-20 alpha-dihydroprogesterone greater than 17 alpha-hydroxyprogesterone greater than 11-deoxycorticosterone. 17 alpha-hydroxy-20 beta-dihydroprogesterone induces the production of maturation-promoting factor leading to GVBD. The 20 beta-dihydro metabolite may be the active metabolite under in vivo condition.

Comparative actions of GABA and acetylcholine on the Xenopus laevis lateral line

The effects of GABA, acetylcholine and carbachol on the spontaneous activity of afferent nerve fibers in the lateral line of Xenopus laevis are characterized. Atropine and bicuculline were also tested on drug- and water motion-evoked activity. GABA (0.019-1.25 mM) suppressed and both acetylcholine (1.25-80 microM) and carbachol (1.25-40 microM) increased spontaneous activity. These actions were blocked by bicuculline (100 microM) and atropine (4 microM) respectively. Atropine (20 microM) and bicuculline (100 microM) had no effect on water motion-evoked activity. The results characterize actions of GABA and acetylcholine not previously described and provide evidence that does not support the hypothesis that GABA or acetylcholine are the afferent transmitter.

Variations in aldosterone and corticosterone plasma levels during metamorphosis in Xenopus laevis tadpoles

Aldosterone and corticosterone plasma levels have been determined by radioimmunoassay at various stages (St) of metamorphosis in Xenopus laevis tadpoles. The aldo level first showed a significant peak at the beginning of the climax (St 58), and again at the middle of the climax (St 61-62); B level increased slightly but significantly at St 59, then showed an important peak at St 62-63. The high levels of these hormones at these stages seem to be associated with the concomitant surge of interrenal synthesis. At this stage, the plasma level of thyroid hormones is maximal, and the main morphological changes occur. Therefore, corticosteroids and thyroid hormones could have synergistic effects on morphogenesis. A relationship is assumed between the surge of corticosterone at the middle of the climax, and the glucocorticoid function of this hormone. Aldosterone could play a part in the differentiation of adult skin.

Myosin isoenzymes in single muscle fibres of Xenopus laevis: analysis of five different functional types

An analysis has been performed of the native myosin isoenzyme composition of isolated skeletal muscle fibres from Xenopus laevis with well-defined isotonic contraction properties. Fast twitch 'white' (type 1) fibres contained three isomyosins; fast twitch 'red' (type 2) fibres showed two major myosin bands with migration velocities very similar to those of the two slower bands in type 1. Slow twitch (type 3) fibres yielded a single, slowly migrating band as did slow tonic (type 5) fibres, whereas the myosin from type 4 (very slow twitch, 'intermediate') fibres migrated with a somewhat higher mobility. The results suggest that amphibian skeletal muscle may possess the principal fibre types found in mammals and birds.

Effects of radius--ulna removal on forelimb regeneration in Xenopus laevis froglets

Regeneration of boneless amputated forearms of adult newts was found to progress at a rate and to a degree comparable to amputated control limbs in which stump bones were not removed. In contrast, regeneration of boneless amputated Xenopus froglet forearms was significantly delayed and did not occur until two to three weeks following amputation. This is in comparison with the initiation of distal cartilage formation observed one week postamputation in control forelimbs of Xenopus froglets. The regeneration of cartilage in boneless forearms of adult newts was found to occur distal to the amputation level. In contrast, distal as well as proximal (centripetal) regeneration of cartilage was observed in the amputated boneless forearms of Xenopus. In froglets and newts, unamputated forelimbs in which forearm bones were extirpated did not initiate cartilage regeneration. Our findings support the hypothesis that forelimb regeneration in Xenopus froglets is primarily a tissue response. In comparison, limb regeneration in the adult newt is predominantly an epimorphic response.

Studies on three kinds of lectins from Xenopus laevis skin

Among skin extracts of various frogs, lectin activity was found only in fractions prepared from Xenopus laevis skin. 3 skin lectins have been separated. Among these, the lectin designated S2-Dlc was isolated in a homogeneous state and showed a preferential agglutination of Ehrlich and S-180 ascites tumor cells; other tumor cells and human erythrocytes were not agglutinated. The lectin-dependent agglutination was inhibited by D-fucose, L-arabinose, D-galactose, lactose and lactulose. The sugar specificity of this lectin is similar to that of the lectin from Xenopus laevis eggs which agglutinates Ehrlich and S-180 ascites cells.

Production of EGF-containing polypeptides in Xenopus oocytes microinjected with submaxillary gland mRNA

The biosynthesis of epidermal growth factor (EGF), a 6045 dalton mitogen produced in the mouse submaxillary gland under androgen regulation, was studied using Xenopus oocytes. Microinjection of total, unfractionated gland mRNA together with [35S]cysteine resulted in the production of a secretory polypeptide of approximately 9000 daltons, specifically immunoprecipitable with anti-EGF antibodies. A minor amount of a similarly immunoreactive 9000 dalton secretory polypeptide was produced from the sucrose gradient 9S fraction of gland mRNA. Other, more intensely labeled polypeptides, a cytoplasmic 125 000 dalton and a secretory 110 000 dalton protein were immunoprecipitated from oocytes injected with the greater than 25S mRNA fraction. The biosynthesis of both can hardly be detected in oocytes injected with unfractionated mRNA. All three polypeptides are produced under androgen regulation and share common immunoreactive properties. Northern blot analysis using a 76 nucleotide synthetic EGF cDNA probe revealed hybridization with a single 28S mRNA species. This, and the apparent interrelation between the three polypeptides, suggest that a gland-specific processing protein, encoded by a 9S mRNA, is required to produce the 9000 dalton pro-EGF from the nascent translation product of EGF mRNA.

The relation between soma position and fibre trajectory of neurons in the mesencephalic trigeminal nucleus of Xenopus laevis

In adult Xenopus laevis the mandibular and ophthalmic branches of the trigeminal nerve were backfilled with CoCl2 or cobaltous lysine and whole brains silver intensified to reveal neurons of the mesencephalic Vth nucleus (mes. V). The nucleus contains about 100 cells arranged in a band extending arch-like from the ventrolateral margin of the optic tectum to the midline. Many cells possess a small number of short dendritic processes that arborize in the tectal neuropil; in some cells one dendrite terminates within the ependyma or ventricle. A single axon arises from each cell and courses in layer 7 to the margin of the tectum. Axon collaterals arise close to the cell body to terminate principally within layer 6, but occasionally also in layers 8 and 9. Collaterals occurring more caudally terminate in layer 6. These findings suggest that mes. V cells acts as tectal interneurons as well as conveying somatosensory information to the tectum from the mouth region. In the dorsal roof of the tectum the trajectory of a fibre is related to the distance of the soma from the midline. Mes. V cells located at the lateral end of the nucleus possess axons that course initially in a mediolateral direction before turning along the ventrolateral margin of the tectum. Cells positioned close to the midline have axons that project rostrocaudally the entire length of the tectum. The axons of cells located at intermediate positions within the nucleus course at correspondingly oblique angles through the dorsal roof of the tectum. Thus in this area there is a more or less 90 degrees rang in the orientation of mes. V fibres to the longitudinal axis. It is proposed that this topographical relationship between soma position and axon trajectory arises through a developmental mechanism, in which mes. V fibres grow during larval life sequentially into the medial zone of tectal growth and become subsequently displaced rostrolaterally, owing to the further addition of tectal tissue medially, through an angle dependent upon the parent cell's date of birth.

Structural basis of the activation wave in the egg of Xenopus laevis

A series of changes in the surface of activated Xenopus eggs was observed. Within a few seconds of prick activation a light area appears near the pricking point and expands as a circular light zone (light wave). Some 60 s later this is followed by a dark area expanding as a circular dark zone (dark wave). Both waves travel at a rate of about 9 micron/s at 21 degrees C. In the light zone, cortical granules are breaking down, microvilli are elongating, and the egg surface is expanded. On the other hand, the elongated microvilli are reshortening to become globular and the egg surface is contracted in the dark zone.

Effects of light-deprivation on development of photopositive behavior in Xenopus laevis tadpoles

The development of amphibian sensory systems and behavior is generally considered to proceed normally without reference to sensory experience during embryonic or larval stages. Most of the supporting research, however, has concentrated on the retinotectal (visual) systems of anurans and has ignored behaviors directed by other sensory systems. We demonstrate that early exposure to light is necessary for the development of photopositive behavior in Xenopus laevis tadpoles, a behavior probably directed by the pineal complex. Light-deprivation during the tadpoles' first 10 days of development results in a long-lasting reduction in the tadpoles' light preference. The development of a strong light preference is not influenced by light-deprivation before the tadpoles are 2 days old or after the tadpoles are 10 days old, but light-deprived tadpoles recover a weak light preference after subsequent days of rearing in the light. Lengthening the tadpoles' exposure to light during the first 10 days of development produces increasingly strong light preferences. Considering the important role of the pineal complex in guiding phototactic behaviors in anurans, we suggest that light-deprivation alters photopositive behavior in Xenopus tadpoles by altering the development of the pineal complex.

Characterization of the intermittent breathing pattern in Xenopus laevis

Xenopus laevis exhibits an extensive repertoire of breathing patterns during voluntary diving-emergence behaviour. In experiments where animals surfaced to breathe at a blowhole fitted with a pneumotachograph, two noticeably different patterns of breathing were observed. In the first (burst breathing), long periods of diving were periodically interrupted by short visits to the surface when a discrete series of evenly spaced ventilations occurred. On other occasions, the same animal might rise to the surface and begin ventilating its lungs, not in discrete bursts, but intermittently over a long period of time (a breathing bout). Minute ventilation during a breathing burst was more than double that of a bout and represents a more active diving-emergence behaviour on the part of the animal. Regulation of the amount of gas exchanged in both breathing styles appears to be due to manipulation of the temporal pattern of lung ventilations (i.e. the breath-hold durations), rather than to an alteration in the overall depth of breathing; the latter is possible to some extent, however, through adjustments in the composition of individual ventilations.

Functional conflicts between feeding and gas exchange in suspension-feeding tadpoles, Xenopus laevis

Air-breathing tadpoles of Xenopus laevis (Amphibia: Anura) use buccopharyngeal surfaces for both gas exchange and capture of food particles in the water. In dense food suspensions, tadpoles decrease ventilation of the buccopharynx and increase air breathing. The lung ventilatory frequency is elevated even though the rate of oxygen consumption is at or below resting levels, suggesting that the lung hyperventilation reflects compensation for decreased buccopharyngeal respiration rather than an increased metabolic requirement. If tadpoles in hypoxic water are prevented from breathing air, they increase buccopharyngeal respiration at the expense of feeding. Aerial respiration evidently permits the buccopharyngeal surfaces to be used primarily for food entrapment.

Two healing patterns correlate with different adult neural connectivity patterns in regenerating embryonic Xenopus retina

Nasal and temporal one-third-sized eye fragments, formed by ablation at stage 32-33 of Xenopus laevis embryos, heal and, in about 50% of the cases, survive to make eyes in the postmetamorphic animal which have mappable visuotectal projections. The majority of nasal one-third eyes have duplicate projections whereas the majority of temporal one-third eyes have unduplicated projections. Most nasal one-third eye fragments and a minority of temporal eye fragments heal by the extrusion of cells from the center of the cut edge into the region of the ablation, forming a tongue of cells between the distal cut edges. This healing pattern is correlated with duplicated visuotectal projections. Most temporal one-third fragments and a minority of nasal one-third fragments heal by rounding up; that is, the distal cut edges collapse to meet in the region of the ablation. This healing pattern is correlated with the formation of unduplicated visuotectal projections. During tongue formation, neurons and undifferentiated cells are transferred from the original fragment into the tongue in a disorderly array, but quickly re-form normal retinal order. We propose that the tongue cells retain their original determination to connect to the same tectal positions as the fragment from which they originated, despite their new positions, and that this mosaicism, coupled with cell movement into the tongue, established duplicate visuotectal projections.

Biosynthesis of thyrotropin releasing hormone in the skin of Xenopus laevis: partial sequence of the precursor deduced from cloned cDNA

Skin of Xenopus laevis contains relatively large quantities of thyrotropin releasing hormone (TRH). Total mRNA isolated from skin was cloned in the plasmid pUC8. Among 1400 cDNA clones, one was found with an insert of 478 nucleotides coding for the amino-terminal part of prepro-TRH. This clone was detected using a mixture of two synthetic undecanucleotides for colony hybridization. The single open reading frame starts with a methionine residue and a stretch of hydrophobic amino acids, as is typical for signal peptides, and terminates at the poly(C) tail without a stop codon. The deduced polypeptide of 123 amino acids contains three copies of the sequences Lys-Arg-Gln-His-Pro-Gly-Lys Arg-Arg and a fourth incomplete copy at the carboxyl end. Typical pro-hormone processing at this sequence would yield pGlu-His-Pro.NH2,i.e. TRH. It is concluded that the cloned part of the mRNA codes for prepro-TRH and that the TRH precursor from skin of X. laevis is a polyprotein containing at least four copies of the end product in its amino acid sequence.

The modifications of cortical endoplasmic reticulum during in vitro maturation of Xenopus laevis oocytes and its involvement in cortical granule exocytosis

In Xenopus laevis eggs, cisternae shells which surround cortical granules (CG) are part of a cortical endoplasmic reticulum (ER) network. In this paper the origin of such ER shells has been studied in full-grown, progesterone-exposed Xenopus oocytes. Furthermore, the possible role of the cortical ER in the activation process has been investigated by pricking maturing oocytes. It has been shown that in full-grown ovarian oocytes ER CG shells are absent and ER cisternae are extensively and randomly distributed throughout the peripheral cytoplasm, where they appear to be continuous with annulate lamellae (AL). Following hormone treatment, the AL completely disaggregate and the ER cisternae gradually migrate to the cortex where they surround the CG constituting the typical cortical network described in uterine eggs. Furthermore, it has been found that 8 h after progesterone treatment (before the first polar body extrusion) the response to pricking (CG exocytosis) occurs only at the animal half; there is no observable response in the vegetal half. At this time ER shells surround CG only in the animal hemisphere. A complete CG exocytosis occurs following the first polar body emission, when the cortical ER is well organized in the whole oocyte cortex. The correlation between the differentiation of the cortical ER and the arousal in the oocyte of the ability to respond to a pricking stimulus is discussed in the light of an involvement of the cortical ER in the propagation of CG exocytosis.

Platanna (Xenopus laevis) as a test organism for determining the embryotoxic effects of environmental chemicals

It has been successfully demonstrated that platanna (Xenopus laevis) allows the artificial induction of spawning at any time during the year. The number of eggs collected from a female ranged between 500 and 2400, the fertilization rate varying between 10 and 85%. When unaffected by chemicals, the embryonic development of the larvae took between 8 and 30 weeks. Di(2-ethylhexyl) phthalate (DEHP), methylmercury chloride, and the thalidomide analog EM 12 were used for the experiments described. DEHP at a concentration of 2 ppm retarded the development of the larvae and caused reduced pigmentation of the tadpoles. Methylmercury chloride has been found to have teratogenic and embryolethal effects at a concentration as low as 0.01 ppm. The following teratogenic effects have been determined: bent tails of the larvae, retarded development of the filter system, disturbed osmotic regulation, deranged positional and spatial orientation. EM 12 has been proven to have embryolethal effects at concentrations around 100 ppm. At lower concentrations this substance has teratogenic effects, i.e., it interferes in various ways with the development of the limbs.

[Evaluation of amputation techniques for the study of limb regeneration in the newt and toad]

A comparison between forelimb amputations through the radius-ulna and the humerus was made in the adult newt, Cynops pyrrhogaster pyrrhogaster and the young toad, Xenopus laevis. Newts regenerated their forelimbs after the amputations and the new parts resembled the old in structure and function. Toads regenerated their forelimbs incompletely after the amputations. The new parts lacked joints and fingers showing a simply elongate pattern. The effect of re-amputation of exposed bone on the regeneration was evaluated in the adult newt. A left forelimb was amputated through the humerus and the exposed bone which protruded from the cut surface due to the relationships of the soft tissues, was then re-amputated a few minutes later. A right forelimb of the same individual was simply amputated without re-amputation of the exposed bone. Newts regenerated both forelimbs simultaneously. The new parts resembled the old in structure and function.

Xenopsin: the neurotensin-like octapeptide from Xenopus skin at the carboxyl terminus of its precursor

We have synthesized two oligodeoxyribonucleotide mixtures that contain sequences complementary to different parts of the hypothetical mRNA sequence of xenopsin, a biologically active octapeptide found in skin extracts from Xenopus laevis. The two primer pools were independently used to initiate reverse transcription on skin poly(A)+ RNA and the resulting cDNAs were then used to screen in parallel a cDNA library prepared from skin poly(A)+ RNA. One of the clones that hybridized with both probes was subjected to sequence analysis. It contains a nearly full-length DNA copy of a mRNA of approximately equal to 490 nucleotides that encodes a xenopsin precursor protein. The deduced precursor is 80 amino acids long, exhibits a putative signal sequence at the NH2 terminus, and contains the biologically active peptide at the COOH terminus. The region corresponding to the NH2-terminal portion of the xenopsin precursor shows a striking nucleotide and amino acid sequence homology with the precursor of PYLa, another recently described peptide from Xenopus skin.

Androgen and gonadotropin effects on male mate calls in South African clawed frogs, Xenopus laevis

Mate calling is a prominent reproductive behavior of male South African clawed frogs. Calls consist of alternating slow- and fast-amplitude-modulated trills. Each trill is made up of a series of clicks. The effects of administration of exogenous gonadotropin and androgen on mate calling were studied in male Xenopus laevis. Males were paired with unreceptive female frogs to elicit maximal calling. The amount of time each animal spent calling during the testing period, the peak fundamental frequency of the calls, the rate of calling, and the interclick interval (ICI, a measure of the temporal patterning of the calls) were measured in intact, castrated, and hormone-replaced frogs. Injection of human chorionic gonadotropin (HCG) into intact frogs increased the amount of time spent calling and the ICI relative to measures taken after water injection. Castrated males did not call even when given HCG. Testosterone and dihydrotestosterone treatment reinstated calling in castrates and increased circulating levels of androgens. When androgen-replaced castrated males were injected with HCG, the amount of time spent calling increased and approached levels of intact, HCG-injected males. The above results suggest that androgens are necessary for the production of calls. Gonadotropins appear to play an important role in mate calling, a role at least partly independent of effects on testicular androgen synthesis.

Regulation of cell cycle by cytoplasmic components in the amphibian eggs

Injections of extracts of Xenopus egg cytoplasm induce precocious cleavage furrows in activated Pleurodeles eggs. This cleavage timing system (CTS) activity is retained in two distinct fractions separated by gel filtration. Acceleration of the first cell cycle of the Pleurodeles egg is directly related to the concentration of the injected extracts. However, the maximum advance of the cleavage cycle does not exceed 25 to 30% of the control cycle. Preliminary characterization of these fractions indicates that the CTS effect is abolished after protease but not RNAse treatment, and that the CTS factors are thermostable. The phase of the egg cell cycle sensitive to the CTS factors, which act as a 'clock system mechanism', is discussed.

Transcription in oocytes of highly methylated rDNA from Xenopus laevis sperm

The genes for ribosomal RNA exist as multiple copies in the genome. Each repeated unit comprises a region that codes for the 40S rRNA precursor, and a spacer region of uncertain function (Fig. 1a). In Xenopus laevis there are about 1,000 copies of the dinucleotide sequence C-G in each repeat unit, and of these about 250 can be tested for the presence of 5-methylcytosine using restriction endonucleases. Most of the detectable C-Gs are heavily methylated, but in somatic cells unmethylated C-Gs occur in a 60 base pair (bp) sequence (NTS-60) that is repeated in the spacer. In contrast, the spacer of sperm rDNA is heavily methylated at these and all other testable C-Gs. Loss of methylation at NTS-60 takes place during the first day of embryonic development, near the time when rDNA transcription begins. In an attempt to assess the significance of this developmental change in methylation, we have isolated sperm rDNA and investigated whether it can be transcribed in oocytes. We have found that sperm rDNA is transcribed as efficiently as cloned rDNA, although no loss of methylation was detectable. Direct sequencing of sperm rDNA showed that all 19 C-GS in the promoter are highly methylated. Thus, in the case of rDNA injected into oocytes, loss of methylation is unnecessary for effective transcription.

Changes of alanine-sodium co-transport during maturation of Xenopus laevis oocytes

Maturation of full grown Xenopus oocytes is associated with a decrease of their capacity to transport amino acids and nucleosides. Nevertheless, the transport continues at a reduced rate until the time of metaphase arrest when the oocytes are ready for shedding. We have found that the L-alanine transport in unfertilized, shed oocytes is a saturable process which is Na+-dependent. The stoichiometrical ratio between sodium and alanine is 2:1. Comparison with the alanine uptake in full grown oocytes shows that during maturation Vmax is strongly reduced while Km and the stoichiometrical ratio of sodium and alanine is unaffected. Lowering the osmolarity of the shedding medium reduces the rate of uptake of alanine below the rates seen after shedding into isotonic media. The transport rates amongst the individual oocytes differ. They do not fit to a Gaussian distribution. In addition, in individual oocytes, there exists no correlation between the variations of the transport rates for amino acids and nucleosides, which are also taken up by the unfertilized, shed oocytes.

[Essential and substituted amino acids as chemical stimuli in the clawed frog Xenopus laevis]

Studies have been made of the effect of all 20 natural amino acids on motor activity of the clawed toad Xenopus laevis. It was demonstrated that essential amino acids act as more effective chemical stimuli than replaceable ones.

[Radioautographic study of the cell proliferation of the pigment epithelium of the retina in albino clawed frogs]

The proliferative activity of pigment epithelium was studied by means of 3H-thymidine autoradiography after the removal of retina, lens and iris with the ciliary-terminal zone in the adults. The cell population of pigment epithelium was shown to be heterogeneous on the level of proliferative activity. A low level of proliferation is characteristic of the cells of epithelial monolayer and the cells leaving it and forming aggregates. An intensive local proliferation leading to the formation of expansions was found in the pigment epithelium layer in 7% of cases. On the 20th day after the operation, the index of labelled nuclei in the expansions amounted to 43.4--59.3% and the mitotic index to 1.4--2.1%. On the 75th day elements of atypical retinal differentiation, besides the high proliferative activity, were observed in one expansion.

Changes in polyamine content during limb regeneration in adult Xenopus laevis

Polyamine contents in the regenerates were determined at various stages after amputation of the forelimbs of the adult female Xenopus laevis. Putrescine, spermidine, spermine, and sym-homospermidine were detected in all the specimens examined. Cadaverine was detected only in a limited number of samples. At 5 days after amputation of forelimbs, well before the formation of regenerates, the putrescine content in the stump tissues increased, followed by the increase in spermidine content. The putrescine level in the forelimb regenerates was highest between 30 and 50 days after amputation, and then decreased. The spermidine concentration in the regenerates was about 20 times greater than that in intact forelimbs all throughout the experiments. The concentration of spermine was initially lower than that of both putrescine and spermidine and further decreased soon after amputation. The concentration of sym-homospermidine was originally very low and increased slightly during regeneration. The significance of these results, with respect to the function of polyamines in forelimb regeneration of Xenopus laevis, is discussed.

Lens forming transformations in larval Xenopus laevis induced by denatured eye-cup or its whole protein complement

Implants of lensectomized eye placed between the outer and inner cornea, denatured by ethanol treatment and implants of total protein pellets from homogenates of lensectomized eyes, induce lens-forming transformations of the outer cornea of larval Xenopus laevis.

Abnormal visual input leads to development of abnormal axon trajectories in frogs

Throughout the normal vertebrate brain, visual maps form the left and right eyes overlap and are in register with one another. Visual input has a major role in the development of the pathways which mediate these binocular projections. A dramatic example of the developmental role of sensory input occurs in the isthmo-tectal projection, which is part of the polysynaptic relay from the eye to the ipsilateral tectum of the frog, Xenopus laevis. If one eye is rotated when the animal is still a tadpole, the isthmic axons respond by changing the topography of their terminations in the tectum; for example, a given isthmo-tectal axon which normally would connect with medial tectum can be induced to terminate in lateral tectum. Such rearrangements bring the ipsilateral visual map into register with the contralateral retinotectal map, even though one eye has been rotated. Indirect evidence has suggested that after early eye rotation, isthmo-tectal axons do not grow directly to their new tectal targets but instead reach those targets by routes which pass through their normal termination zones. Here I have used anterograde horseradish peroxidase labelling of isthmo-tectal fibres to show the trajectories of such axons and to compare them with the routes which axons take when allowed to develop normally. Tracings of individual axons in flat-mounted, unsectioned tecta show that most axons in normal Xenopus follow fairly straight paths in the tectum. In contrast, early eye rotation causes many isthmo-tectal axons to follow crooked, circuitous pathways before they terminate.

Mechanical, electrical, and morphological characteristics of skeletal muscle fibers from Xenopus and other species of frogs

Mechanical, electrical, and morphological properties of iliofibularis or semitendinosus of Xenopus laevis, Rana catesbeiana, and Rana nigromaculata were investigated in an attempt to find out the differences between them which will give the basic knowledge for the study of excitation-contraction coupling. With application of electrical stimulation, a single muscle fiber from Xenopus contracted at a faster rate of rise than did the other muscles tested. The maximum rate of rise (Tmax) of tension was in the order of Xenopus, R. catesbeiana, and R. nigromaculata. Ca2+ sensitivity and Tmax of mechanically skinned fibers of Xenopus resembled those of R. catesbeiana. Xenopus muscle had a small cross-sectional area of T-tubule compared with that in other species and the action potential exhibited a small positive-going hump. The volume density of the terminal cisternae of sarcoplasmic reticulum (SR) to the myofibril was the largest in the Xenopus muscle, with a statistically significant difference. Therefore, the Xenopus muscle appears to be good material for investigation of mechanisms related to Ca2+ release from SR, as elicited by the excitation of T-tubules.

Trifluoperazine-induced meiotic maturation in Xenopus laevis

Xenopus oocytes were exposed to trifluoperazine, a drug that binds to the calcium-regulating protein, calmodulin. The drug induced meiotic maturation even in the absence of progesterone. When trifluoperazine was microinjected directly into oocytes the maturation of the cells was partially inhibited in that the white spot, indicative of germinal vesicle breakdown, did not appear even though the germinal itself was absent in dissected oocytes.

Potassium permeability in thin amphibian myelinated fibres

Potential clamp analysis of thin (10-12 micrometers) myelinated fibres from amphibia (Xenopus laevis and Rana temporaria) showed that they had a large delayed K-permeability (PK) and a PK/PNa-ratio of 0.32, which is similar to the ratio in large (25-30 micrometers) frog fibres. These results agree with earlier evidence of a large delayed PK in 10-15 micrometers Rana fibres; a recent description of a size-dependent difference in PK was thus not confirmed. The large PK (0.32 cm3s-1 X 10(-9) in 10-12 micrometers amphibian fibres contrasted with the small PK (0.05 cm3 s-1 X 10(-9) in 12 micrometers rat fibres. Frog and toad fibres also had a larger nodal capacitance (4 pF), but smaller leak conductance (18 nS) than rat fibres (1.4 pF and 29 nS). These differences may be related to the morphological evidence of a more open node with a larger surface area in the amphibian as compared to the rat node.

The T-SR junction in contracting single skeletal muscle fibers

The junction between the T system and sarcoplasmic reticulum (SR) of frog skeletal muscle was examined in resting and contracting muscles. Pillars, defined as pairs of electron-opaque lines bounding an electron-lucent interior, were seen spanning the gap between T membrane and SR. Feet, defined previously in images of heavily stained preparations, appear with electron-opaque interiors and as such are distinct from the pillars studied here. Amorphous material was often present in the gap between T membrane and SR. Sometimes the amorphous material appeared as a thin line parallel to the membranes; sometimes it seemed loosely organized at the sites where feet have been reported. Resting single fibers contained 39 +/- 14.3 (mean +/- SD; n = 9 fibers) pillars/micrometer2 of tubule membrane. Single fibers, activated by a potassium-rich solution at 4 degrees C, contained 66 +/- 12.9 pillars/micrometer2 (n = 8) but fibers contracting in response to 2 mM caffeine contained 33 +/- 8.6/micrometer2 (n = 5). Pillar formation occurs when fibers are activated electrically, but not when calcium is released directly from the SR; and so we postulate that pillar formation is a step in excitation-contraction coupling.

The effect of temperature on the contractile response of cardiac muscle from two frog species, Rana temporaria and Xenopus laevis, at two different calcium concentrations-II. At pH 7.0 and pH 6.6

1. Mechanical parameters were recorded from paced ventricular cardiac muscle strips of two amphibian species. Rana temporaria and xenopus laevis. 2. The strips contracted at pH 6.6 and 7.0 with either 1.6 or 3.0 mM Ca2+ while the temperature was changed from 5 to 30 degree C. 3. In the hearts of R. temporaria, but not in those of X. laevis, in increased Ca2+ concentration at low pH could compensate for the effect of lowered pH. 4. It is concluded that during high CO2 tension and/or low pH the myocardium of X. laevis was more temperature dependent, less Ca2+ dependent in the Ca2+ range examined and less sensitive to the pH and/or the CO2 tension during physiological temperature and Ca2+ concentration, than the cardiac muscle of R. temporaria.

The effect of temperature on the contractile response of cardiac muscle from two frog species, Rana temporaria and Xenopus laevis, at two different calcium concentrations-I. At pH 7.7

1. Mechanical parameters were recorded from paced ventricular cardiac muscle strips of two amphibian species. Rana temporaria and Xenopus laevis. 2. The strips contracted at pH 7.7 and with either 1.6 or 3.0 mM Ca2+ while the temperature was changed from 5 to 30 degree C. 3. It is concluded that the cardiac muscles of the two frog species exhibited similar contractile responses upon temperature and Ca2+ elevations at physiological pH, although X. laevis hearts displayed greater variation in tension response than those of R. Temporaria. 4. The relaxation mechanisms in relation to the contractile mechanisms of X. laevis myocardium, however, seemed to be more efficient, although more sensitive to low temperatures than those of R. temporaria.

Modulation of the neural control of the clasp reflex in male Xenopus laevis by androgens: a multidisciplinary study

The neural control of the clasp reflex in male Xenopus laevis has been studied by using anatomical, electrophysiological, and biochemical techniques. Neurons in spinal segment 2 of castrated males accumulate label after injection of [3H]-dihydrotestosterone; these neurons are distributed within the rostral portions of the motoneuronal pools of the sternoradialis and flexor carpi radialis muscles. In vitro recordings from the nerve to the sternoradialis muscle in the isolated spinal cord preparation from castrated male Xenopus showed increased activation to paired dorsal root stimulation after addition of dihydrotestosterone to the bath. This increase could be prevented by prior administration of cycloheximide. The reducing enzyme testosterone 5 alpha-reductase is present and is selectively distributed in male Xenopus spinal cord. It is speculated that the androgens may alter patterns of neuronal activity leading to the "clasp" muscles and thereby influence myosin types within these muscles.

Experimental analysis of the lens-forming competence of the cornea, iris, and retina in Xenopus laevis tadpoles

The present research was carried out using Xenopus laevis tadpoles at stage 50-51 to ascertain whether eye territories other than the outer cornea and the pericorneal epidermis have lens-forming competence, particularly the iris and/or retina. Five experiments were performed: simple lentectomy; removal of lens, outer cornea, and pericorneal integument; removal of lens, outer cornea, and pericorneal integument, and simultaneous incision of retina; removal of lens, outer cornea and pericorneal integument, and simultaneous incision of dorsal iris; removal of lens and simultaneous lesion of iris and retina. Results show that when lentectomy is performed without damaging any territories other than the outer and inner cornea, lens regeneration is always from the outer cornea, and the iris and retina do not exhibit any lens-forming competence. The iris and retina show no clear-cut lens-forming competence even after they have been stimulated by comparatively extensive lesions.

The development of the retinotectal projections from compound eyes in Xenopus

The retinotectal projections from double-nasal (NN), double-temporal (TT) and double-ventral (VV) compound eyes in Xenopus were studied autoradiographically and electrophysiologically during development. Early TT projections were confined to rostrolateral tectum and spread with advancing age to cover most of the tectum by shortly after metamorphosis. Early VV projections showed a decreased density of label on lateral tectum. Early NN projections appeared to extend across the entire rostrocaudal length of the available tectum at all stages of development, but showed a decrease in label density on rostral tectum. The results are discussed in relation to various hypotheses about the formation of retinotectal connexions.

Pineal complex of the clawed toad, Xenopus laevis Daud.: structure and function

The morphological and physiological properties of the pineal complex of Xenopus laevis were investigated in larval, juvenile and adult animals. In a representative majority of adult X. laevis, the frontal organ does not display signs of degeneration. Fully differentiated frontal organs contain photoreceptors typical of the pineal complex of lower vertebrates. By means of the acetylcholinesterase (AChE)-reaction approximately 30 neurons of two different types were demonstrated in the frontal organ. The frontal-organ nerve is composed of approximately 10 myelinated and 40 unmyelinated nerve fibers. The neuropil areas of the frontal organ are generally similar to the corresponding structures of the intracranial epiphysis. The neuronal apparatus of the epiphysis cerebri of X. laevis consists of (i) photoreceptor cells, (ii) approximately 100 AChE-positive neurons, (iii) complex neuropil areas, and (iv) a pineal tract formed by approximately 10 myelinated and approximately 100 unmyelinated nerve fibers. Some of them exhibit granular inclusions indicating that pinealopetal elements may enter the pineal complex of X. laevis via this pathway. The topography of the pineal tract of X. laevis differs considerably from that in ranid species. The most conspicuous element of the plexiform zones is the ribbon synapse. The basal processes of the photoreceptor cells may be presynaptic elements of simple, tangential, dyad or triad synaptic contacts. Conventional synapses were observed only occasionally. Electrophysiological recordings revealed that the pineal complex of Xenopus laevis is directly sensitive to light. In response to light stimuli, two types of responses, achromatic and chromatic, were recorded from the nerve of the frontal organ. In contrast, the epiphysis exhibited only achromatic units. The opposed color mechanism of the chromatic response showed a maximum sensitivity at approximately 360 nm for the inhibitory and at 520 nm for the excitatory event. The action spectrum of the achromatic response of the epiphysis and the frontal organ peaked between 500 and 520 nm and showed no Purkinje-shift during dark adaptation. The functional significance of these phenomena is discussed.

Germinal vesicle breakdown in the Xenopus laevis oocyte: description of a transient microtubular structure

During progesterone-induced meiotic maturation of Xenopus oocytes in vitro, 7 morphological stages were defined. Using cytological analysis, nuclear breakdown was divided into three stages. Stage 1 corresponded to basal germinal vesicle breakdown. Stage 2 was characterized by the advent and development of a fibrillar network formed by microtubules at the basal part of the nucleus. Below, a lamellar microtubule organizing center (MTOC) was present. Numerous vesicles of smooth endoplasmic reticulum were proximal to both of these structures. During its formation and modification (stages 2 and 3), the fibrillar network migrated towards the animal pole. A prometaphase 1 stage was observed before the formation of the metaphase 1 spindle.

The Role of Lactic Acid Accumulation in Muscle Fatigue of Two Species of Anurans, Xenopus Laevis and Rana Pipiens

Fatigue produced a marked increase in the lactic acid content of hindlimb muscles, the blood, and the whole animal. After 15 min of rest there was little decline of lactic acid levels but the animals could be stimulated into about 3 min of intense activity. This re-fatigue produced a further increase in lactic acid levels. Gastrocnemius muscles removed from fatigued frogs and stimulated in vitro were able to generate initial tensions similar to those in control muscles; total tension was about a third of the control value. In vitro stimulation of these muscles from fatigued frogs led to additional accumulation of lactic acid. Fatigue produced little decrease in the glycogen content of muscles in X. laevis but a marked decrease in R. pipiens. Considerable glycogen stores remained even in the muscles of re-fatigued animals. These data show that accumulation of lactic acid in muscle or blood, depletion of glycogen in muscle, or change in blood pH cannot account for fatigue in these species. Possible other causes of fatigue are discussed.