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SUMMARY: Vascular endothelial growth factor (VEGF) and its receptor, VEGFR-2, are known to regulate blood vessel endothelium growth. They play important role in human and rodents teeth development. In newt jaws, there are sequential developmental teeth germs following behind the mature teeth. We examined the immunohistochemical localization of VEGF and its receptor and showed the specific expression pattern of VEGF and VEGF receptor in Cynops pyrrhogaster sequential tooth development. The intensity of immunoreactivity for VEGF in the inner enamel epithelium was weaker than that in the outer enamel epithelium in the dentine matrix formation and mineralization stages. Finally, at the enameloid maturation and enamel-like matrix formation stage, immunoreactivity for VEGF in inner enamel epithelium was stronger than in the outer enamel epithelium. The intensity of immunoreactivity for VEGFR-2 was positive for the outer enamel epithelium throughout tooth development. The crown sides of the odontoblasts were stained especially strongly for VEGF and VEGFR-2 during the dentine matrix formation and mineralization stage of the enameloid maturation and enamel- like matrix formation stage. We postulate that the expression of VEGF in the inner enamel epithelium and odontoblast widely effects tooth development in newts, as well as in human and rodents.

RESUMEN: Se sabe que el factor de crecimiento endotelial vascular (VEGF) y su receptor, VEGFR-2, regulan el crecimiento del endotelio de los vasos sanguíneos. Desempeñan un papel importante en el desarrollo de los dientes humanos y de los roedores. En las mandíbulas de tritón, hay gérmenes dentales de desarrollo secuenciales que siguen a los dientes maduros. Examinamos la localización inmunohistoquímica de VEGF y su receptor y mostramos el patrón de expresión específico de VEGF y receptor de VEGF en el desarrollo secuencial de dientes de Cynops pyrrhogaster. La intensidad de la inmunorreactividad para VEGF en el epitelio interno del esmalte era más débil que en el epitelio externo del esmalte en las etapas de formación y mineralización de la matriz de dentina. Finalmente, en la etapa de maduración del esmalte y de formación de la matriz similar al esmalte, la inmunorreactividad para VEGF en el epitelio interno del esmalte fue más fuerte que en el epitelio externo del esmalte. La intensidad de la inmunorreactividad para VEGFR- 2 fue positiva para el epitelio externo del esmalte durante el desarrollo del diente. Los márgenes de la corona de los odontoblastos se tiñeron especialmente para VEGF y VEGFR-2 durante la etapa de formación de la matriz de dentina y mineralización de la etapa de maduración del esmalte y la etapa de formación de la matriz similar al esmalte. Postulamos que la expresión de VEGF en el epitelio interno del esmalte y odontoblastos afecta ampliamente el desarrollo de los dientes en tritones, así como en humanos y roedores.

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Tetrodotoxin (TTX), one of the most toxic substances in nature, is present in bacteria, invertebrates, fishes, and amphibians. Marine organisms seem to bioaccumulate TTX from their food or acquire it from symbiotic bacteria, but its origin in amphibians is unclear. Taricha granulosa can exhibit high TTX levels, presumably concentrated in skin poison glands, acting as an agent of selection upon predatory garter snakes (Thamnophis). This co-evolutionary arms race induces variation in T. granulosa TTX levels, from very high to undetectable. Using morphology and biochemistry, we investigated differences in toxin localization and quality between two populations at the extremes of toxicity. TTX concentration within poison glands is related to the volume of a single cell type in which TTX occurs exclusively in distinctive secretory granules, suggesting a relationship between granule structure and chemical composition. TTX was detected in mucous glands in both populations, contradicting the general understanding that these glands do not secrete defensive chemicals and expanding currently held interpretations of amphibian skin gland functionality. Skin secretions of the two populations differed in low-mass molecules and proteins. Our results demonstrate that interpopulation variation in TTX levels is related to poison gland morphology.

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The morphological and histological structure of the brains of Bufo gargarizans and Cynops orientalis were observed by anatomy and light microscopy. The results show that the brains of Bufo gargarizans and Cynops orientalis are divided into 5 parts which include the telencephalon, diencephalon, mesencephalon, cerebellum and medulla oblongata. The telencephalon consists of the olfactory bulb and the cerebral hemisphere. The olfactory bulb is developed that has two pairs of olfactory nerve. Bufo gargarizan has a symmetrical oval hemisphere optic lobes; Cynops orientalis only has a spherical optic lobe. The cerebellum is situated behind the optic lobe and closely connected with the myelencephalon. In this paper, the morphological and histological differences between the two species are discussed. The proportion of cerebral hemisphere is gradually increasing, which correlated with a progressive increase in the number of neuronal cell classes, and reflected in behavior complexity.

La estructura morfológica e histológica de los cerebros de Bufo gargarizans y Cynops orientalis se observó mediante anatomía y microscopía óptica. Los resultados muestran que los cerebros de Bufo gargarizans y Cynops orientalis se dividen en 5 partes, que incluyen el telencéfalo, diencéfalo, mesencéfalo, cerebelo y mielencéfalo. El telencéfalo consiste en bulbo olfatorio y hemisferio cerebral. El bulbo olfatorio tiene dos pares de nervios olfatorios. Los lóbulos ópticos de Bufo gargarizans son ovalados y simétricos en ambos hemisferios cerebrales; Cynops orientalis tiene solo un lóbulo óptico esférico. El cerebelo está situado detrás del lóbulo óptico y está estrechamente conectado con el mielencéfalo. En este trabajo, se discuten las diferencias morfológicas e histológicas entre las dos especies. El tamaño del hemisferio cerebral aumenta gradualmente, lo que se correlaciona con un aumento progresivo de células neuronales en los núcleos, reflejándose en la complejidad del comportamiento.

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Chytridiomycosis is an infectious disease of amphibians caused by the fungal species Batrachochytrium dendrobatidis and B. salamandrivorans and has been implicated in the population decline of amphibian species worldwide. This case report describes a successful treatment protocol for chytridiomycosis in laboratory-maintained colonies of axolotls (Ambystoma mexicanum) and rough-skinned newts (Taricha granulosa). Over 12 mo, axolotls (n = 12) in a laboratory-reared colony developed multifocal erythematous dermatitis, mainly on the distal limbs and tails. Wild-caught newts handled by the same lab personnel were housed in an adjacent room and occasionally presented with abdominal distension and lethargy. Differentials included poor water quality, pathogen infection, parasitic infestation, and trauma. Antibiotic treatment of animals according to results of bacterial culture and sensitivity, combined with bleach disinfection of aquaria, did not resolve clinical signs. Skin swabs from clinically affected axolotls submitted for a newly available commercial screen were positive for B. dendrobatidis. Additional PCR and sequencing analysis revealed chytrid-positive animals among group-housed newts in 2 clinically unaffected aquaria and suspected PCR-positives for 2 affected newt aquaria and an additional axolotl. Axolotls with skin lesions (n = 2) and newts with abdominal distension and lethargy (n = 2) underwent experimental treatment with itraconazole submersion (0.002% to 0.0025%; 5 min daily for 10 d). This pilot treatment was well tolerated and led to clinical resolution. Subsequent itraconazole treatment of the entire colony led to regrowth of extremities and restoration of normal coloration among axolotls. During treatment, the facility was decontaminated, and additional biosecurity measures were developed. PCR results after the pilot treatment and subsequent full-colony treatments (at 1 wk, 1 mo, and 6 mo after treatment) were negative for the presence of B. dendrobatidis. Because chytridiomycosis is a reportable animal disease in our state, colonies officially remained quarantined until negative PCR results were obtained at least 6 mo after treatment.

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Anatomical and histological examinations were conducted on the digestive glands of two closely related mountain newts, Neurergus microspilotus (Nesterov, 1916) and Neurergus kaiseri Schmidt, 1952. In N. microspilotus and N. kaiseri the major digestive glands comprise a very large liver and a small pancreas. In both species the liver has two distinct lobes, right and left. Histologically, the parenchyma of the liver of both species is contained within a thin capsule of fibroconnective tissue. Glycogen deposits and fat storage often dissolve during the routine histological process and produce considerable histological variability. Sinusoids are lined with endothelial cells forming a very thin epithelial sheet, with discontinuous basement membrane. Bile ducts also occur within the parenchyma of the liver. The ducts are lined by simple cuboidal epithelium. The gall bladder is a storage depot for bile. Its mucosa is thrown into numerous folds. The epithelial lining of the tunica muscularis is arranged circularly. There is a lot of pigmentation in the hepatic parenchyma. The pancreas in N. microspilotus and N. kaiseri is roughly triangular in shape, and lies rather to the dorsal side of the duodenum, between it and the stomach. The exocrine portion of the pancreas consists of clusters of pyramidal cells, which are mostly organized in acini. In both species the cells have a dark basophilic cytoplasm, distinct basal nuclei, and many large eosinophilic zymogen granules containing enzymes responsible for the digestion of proteins, carbohydrates, fats and nucleotides.(AU)

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Anatomical and histological examinations were conducted on the digestive glands of two closely related mountain newts, Neurergus microspilotus (Nesterov, 1916) and Neurergus kaiseri Schmidt, 1952. In N. microspilotus and N. kaiseri the major digestive glands comprise a very large liver and a small pancreas. In both species the liver has two distinct lobes, right and left. Histologically, the parenchyma of the liver of both species is contained within a thin capsule of fibroconnective tissue. Glycogen deposits and fat storage often dissolve during the routine histological process and produce considerable histological variability. Sinusoids are lined with endothelial cells forming a very thin epithelial sheet, with discontinuous basement membrane. Bile ducts also occur within the parenchyma of the liver. The ducts are lined by simple cuboidal epithelium. The gall bladder is a storage depot for bile. Its mucosa is thrown into numerous folds. The epithelial lining of the tunica muscularis is arranged circularly. There is a lot of pigmentation in the hepatic parenchyma. The pancreas in N. microspilotus and N. kaiseri is roughly triangular in shape, and lies rather to the dorsal side of the duodenum, between it and the stomach. The exocrine portion of the pancreas consists of clusters of pyramidal cells, which are mostly organized in acini. In both species the cells have a dark basophilic cytoplasm, distinct basal nuclei, and many large eosinophilic zymogen granules containing enzymes responsible for the digestion of proteins, carbohydrates, fats and nucleotides.

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The Chinese fire-bellied newt, Cynops orientalis, belonging to Amphibia, Caudata, Salamandridae is a species endemic to China. The liver, which is an important digestive gland and the largest amphibian organ, has various functions, including detoxification, glycogen storage, protein synthesis, and hormone production. However, the newt liver has rarely been studied at the molecular level. We performed histomorphology and high-throughput proteomic analysis of the Chinese fire-bellied newt liver, using hematoxylin and eosin (H&E) staining and two-dimensional electrophoresis coupled with mass spectrometry. The H&E staining showed that the newt liver nuclei are large and round, are located in the lateral cytoplasm, and contain a large quantity of lipid droplets. Melanins were abundantly present throughout the hepatic parenchyma. The proteome analysis showed a total of 545 proteins detected in the newt liver. Furthermore, a gene ontology analysis suggested that these proteins were associated with metabolism, immune response, cellular homeostasis, etc. Among these, proteins with metabolic functions were found to be the most abundant and highly expressed. This supports the role of the liver as the metabolic center. The proteomic results provide new insights into the aspects of the liver proteomes of the Chinese fire-bellied newt. The identification of a more global liver proteome in the newt may provide a basis for characterizing and comparing the liver proteomes from other amphibian species.

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The objective of this study was to explore the relationship between the retinal structure and its life adaptation to the environment of Ctenopharyngodon idella, Cynops orientalis, Bufo bufo gargarizans, Gekko japonicus and Columba livia . Measuring retinal thickness of each layer, the nuclei layer, and the diameter of each nuclear layer of the five animals, the statistical data analysis shows that: the nuclei layers of five animals are all 4, and their structures can be divided to 10 layers when observing with optical microscope. The retinal thickness of Ctenopharyngodon idella was 190.49 mm, Cynops orientalis was 173.07 µm, and the Bufo bufo gargarizans was 195.06 µm, Gekko japonicus was 224.32 µm and Columba livia was 174.10 µm. The number of retinal inner nuclear layers of Bufo bufo gargarizans and Gekko japonicus and Columba livia are more than their outer nuclear layers, on the contrary, retinal inner nuclear layers of Ctenopharyngodon idella and Cynops orientalis are less than their outer nuclear layers. The rod and cone layer of retina of Cynops orientalis were more advanced, but their nerve fiber layer (NFL) degraded highly, revealing a strong photosensitivity but a low visual sensitivity; to Columba livia , their NFL of retina are highly developed, so as their vision. The different structures and functions of the retina of Ctenopharyngodon idella, Cynops orientalis, Bufo bufo gargarizans, Gekko japonicus and Columba livia correspond with their behavioral characteristics and the living environment's change from aquatic to amphibious to land.

El objetivo de este estudio fue explorar la relación entre las estructuras de la retina y su adaptación al medioambiente en Ctenopharyngodon idella, Cynops orientalis, Bufo bufo gargarizans,Gekko japonicus y Columba livia . La medición del espesor de cada capa de la retina, la capa nuclear y su diámetro en los cinco animales, mostró a través del análisis estadístico que las capas nucleares en todos ellos fueron 4, y sus estructuras se pueden dividir en 10 capas cuando se observan con el microscopio óptico. El espesor de la retina de Ctenopharyngodon idella fue 190,49 µm, de Cynops orientalis fue 173,07 µm, de Bufo bufo gargarizans fue 195,06 µm, de Gekko japonicus fue 224,32 µm y de Columba livia fue 174,10 µm. El número de capas nucleares internas de la retina de Bufo gargarizans, Gekko japonicus y Columba livia fue mayor que sus capas nucleares externas, mientras que las capas nucleares internas de Ctenopharyngodon idella y Cynops orientalis fueron menos que las capas nucleares externas. La capa de conos y bastones de la retina de Cynops orientalis fue más desarrollada, pero su capa de fibras nerviosas presentó una elevada degeneración, lo que muestra una gran fotosensibilidad, pero una sensibilidad visual baja. En Columba livia, la capa de fibras nerviosas de la retina estuvo muy desarrollada, y de esta manera, su visión. El grado de desarrollo de las diferentes estructuras y funciones de la retina de Ctenopharyngodon idella, Cynops orientalis, Bufo bufo gargarizans, Gekko japonicus y Columba livia está relacionada con sus características de comportamiento y el cambio de las condiciones de las vidas acuática y anfibia en la tierra.

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The dorsal surface of the tongue gustatory organs of Chinese fire-bellied newt (Cynops orientalis) was observed by employing the light and scanning electron microscopy (SEM) techniques. The results revealed that the rostral and median part of the tongue presents a round apex and covered by taste disks (TDs). They are usually roundish or ellipsoidal in shape and are 20-35 mm in diameter. The many openings of the lingual glands are 4-8 mm in diameter exist in the lateral border or median part of lingual body. The gustatory organs on the tongue did not differed form those presented in other species in Caudates. These may indicate the functions of gustatory organs on the tongue related to their life habit.

La superficie dorsal de la lengua de los órganos gustativos del tritón de vientre de fuego chino (Cynops orientalis) se observó mediante microscopía de luz y electrónica de barrido (SEM). Los resultados revelaron que la parte rostral y mediana de la lengua presenta un ápice redondo y cubierto por discos sensoriales. Estos por lo general tienen una forma redondeada o elipsoidal con un diámetro de 20-35 mm. Las numerosas aperturas de las glándulas linguales tienen un diámetro de 4-8 mm en el margen lateral o en la parte mediana de cuerpo lingual. No se observaron diferencias en los órganos gustativos linguales al comparar estos con otras especies de caudados. Estos pueden indicar funciones de los órganos gustativos de la lengua relacionadas con su hábito de vida.

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In order to further studying the relationship between the gastrointestinal endocrine cells and the hibernation of Chinese fire-bellied newt, histological techniques were used in this study to explore the distributed density and morphology of argentaffine cells in the digestive tract during hibernation and non-hibernation. The argentaffine cells could be observed throughout the digestive tract of Chinese fire-bellied newt during hibernation and non-hibernation and mainly distributed in the acinar epithelial cells, epithelial cells and intrinsic membrane. They had appeared in the shape of goblet, pyramid, ellipse, round, cone-shaped, spindle-shaped. The cytoplasm contains secretory granules at the basal regions with spherical nuclei in the basal regions. Most of them had processes in different directions, suggesting that the argentaffine cells have combined the function of endocrine and exocrine. The distribution density curves of argentaffine cells were generally wavelike during the two periods. It was highest in the body of stomach in hibernation, while in non-hibernation it was highest in the pyloric. Totally the density of argentaffine cells was higher in hibernation period than that in non-hibernation period. The results showed that the activity of the digestive tract was expectedly weakened during the hibernation, but the function of endocrine was actually strengthened.

Con el fin de promover el estudio de la relación entre las células endocrinas gastrointestinales y la hibernación del tritón vientre de fuego chino, fueron utilizados técnicas histológicas para explorar la densidad de distribuición y la morfología de las células argentafines en el tracto digestivo durante la hibernación y la no hibernación. Las células argentafines pudieron ser observadas en todo el tracto digestivo de tritón vientre de fuego chino durante la hibernación y no hibernación, y se distribuyeron principalmente en las células epiteliales acinares, células epiteliales y la membrana intrínseca. Aparecieron de forma caliciforme, piramidal, elíptica, redonda, cónica y de huso. El citoplasma contenía gránulos de secreción en las regiones basales con núcleos esféricos en esa región. La mayoría de ellos tenía procesos en diferentes direcciones, lo que sugiere que las células argentafines combinaron la función del sistema endocrino y exocrino. Las curvas de densidad de distribución de las células argentafines fueron generalmente ondulante durante los dos períodos. Esta fue más alta en el cuerpo del estómago en estado de hibernación, mientras que en la no hibernación fue mayor en el píloro. En total, la densidad de las células argentafines era mayor en el periodo de hibernación. Los resultados mostraron que la actividad del tracto digestivo se debilitó, como era de esperar, durante la hibernación, pero la función del sistema endocrino se fortaleció.

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Worldwide, one in every three species of amphibian is endangered, 39 species have gone extinct in the last 500 years and another 130 species are suspected to have gone extinct in recent decades. Of the amphibians, salamanders have the highest portion of their species in one of the risk categories, even higher than the frogs. To date there have been few studies that have used recent field data to examine the status of populations of endangered salamanders. In this study we evaluate the current situation of two tiny salamanders, Parvimolge townsendi and Thorius pennatulus, both of which are distributed at intermediate elevations in the mountains of the northern Neotropics and are considered to be critically endangered; the first has been proposed as possibly extinct. By carrying out exhaustive surveys in both historical and potentially suitable sites for these two species, we evaluated their abundance and the characteristics of their habitats, and we estimated their potential geographic distribution. We visited 22 sites, investing 672 person-hours of sampling effort in the surveys, and found 201 P. townsendi salamanders in 11 sites and only 13 T. pennatulus salamanders in 5 sites. Both species were preferentially found in cloud forest fragments that were well conserved or only moderately transformed, and some of the salamanders were found in shade coffee plantations. The potential distribution area of both species is markedly fragmented and we estimate that it has decreased by more than 48%. The results of this study highlight the importance of carrying out exhaustive, systematic field surveys to obtain accurate information about the current situation of critically endangered species, and help us better understand the crisis that amphibians are facing worldwide.

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The morphology of Chinese fire-bellied newt liver consists of 5 lobes, with exception of a few individual differences present, which are composed by a number of hepatic lobules. Passing through the center of the lobules, a central vein radiates and is arranged in orderly row from one to several layers. The interval of the hepatic cords or masses are irregular and variable sinusoid. The hepatic sinusoidal wall consists of one layer endothelial cells or Macrophagocytus stellatus (Kupffer cells), which have protrusions and elongations. The intervals of the hepatic cells have perisinusoidal space (space of Disse). The hepatic cell is polygonal in shape with uniform, round or oval nucleus, 17.8­12.4um in diameter, mean 14.2 um 2-6 nucleoli, nuclear-cytoplasmic volume ratio was 0.24:1. There is a lot of pigmentation in the hepatic parenchyma.

La morfología del hígado del tritón de vientre de fuego chino está constituida por 5 lóbulos, excepto unos pocos que presentan diferencias individuales, los cuales se componen de una gran cantidad de lóbulos hepáticos. Pasando por el centro de los lóbulos, se encuentra una vena central radial y los organiza en cordones o placas hepáticas. La vena central es delgada de 61,6-30,2 um de diámetro, con una media 42 de um. Los hepatocitos alrededor de la vena central están organizados en filas ordenadas por una a varias capas. El intervalo de los cordones hepáticos o masas es irregular y sinusoidal variable. La pared del sinusoide hepático está formada por una capa de células endoteliales o macrófagos hepáticos (células de Kupffer) que tienen protuberancias y elongaciones. El intervalo de las células hepáticas tienen el espacio perisinusoidal (de Disse). La célula hepática es de forma poligonal con un núcleo redondo u oval uniforme de 17,8-12,4 um de diámetro, con una media 14,2um. 2 a 6 nucléolos, con un radio de volumen nuclear-citoplasmático de 0,24:1. Hay una gran cantidad de pigmentación en el parénquima hepático.

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Retinoic acid (RA) is a biologically important metabolite of vitamin A that modulates growth and differentiation of many cell types. Although abundant in the CNS of many vertebrates, the precise role of RA in neural development has yet to be elucidated. Moreover, very little information is available regarding the role of RA in invertebrate neural development and regeneration. We have recently demonstrated that RA stimulates neurite outgrowth from adult newt spinal cord explants and may represent a significant factor in vivo in the reciprocal interactions between peripheral nerves and regenerating limb blastema cells. This interaction leads to the restoration of a functional limb after amputation. In support of this model, we have cloned a cDNA for the retinoic acid receptor of the β subtype (RARβ) whose expression is restricted to the spinal cord and brain of the adult newt and may be present in the limb blastema. This receptor may mediate the trophic effects of blastema-derived RA on neurite outgrowth and chemotaxis from spinal cord neurons. We have also extended our studies on the role of RA to the simple nervous system of the mollusc, Lymnaea stagnalis. Preliminary data support a role for RA in the survival, outgrowth, and chemotactic response of single, isolated, identifiable neurons in culture. This work represents the first evidence for chemotaxis and trophic effects of retinoids in an invertebrate nervous system. It is hoped that our work will shed light on the evolutionary conservation of a role for RA in neural development and regeneration.

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The skulls of six species of plethodontid salamanders of the genus Bolitoglossa from Costa Rica and Panama, Bolitoglossa colonnea, B. dofleini, B. lignicolor, B. marmorea, B. schizodactyla and B. striatula are comparatively analysed. All species are terrestrial or slightly arboreal and show no life-mode-dependent skull characteristics. Heads cleared by transparent preparation and stained in toto were used for examination of the skull structure and paraffin sections of the gonads were prepared to confirm sexual maturity of each individual. Focussing on the size of the premaxillary pars dentalis, the degree of fusion of the processus dorsales praemaxillares and the presence or absence of the paired prefrontals we state that B. dofleini and B. striatula possess more ancestral characteristics, B. marmorea is situated in an intermediate position and B. colonnea, B. lignicolor and B. schizodactyla show more advanced characteristics.

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Aterosclerose é uma doença coronária onde a deposiçäo de lipídeos nas artérias leva a problemas na circulaçäo sanguínea. O presente trabalho avalia a açäo dos flavonóides morina, quercetina e ácido nicotínico isoladamente e em associaçäo no metabolismo lipídico em ratos hiperlipidêmicos. Foram analisados os níveis de colesterol, colesterol HDL e tricilfliceróis no soro sanguíneo após administraçäo via intraperitoneal, dos compostos flavononoídicos dissolvidos em propileno glicol na dose de 5mg/kg de peso corporal. Quercetina mostrou o maior percentual de reduçäo do colesterol. para colesterol HDL os melhores resultados foram obtidos com ácido nicotínico isoladamente, enquanto a associaçäo morina-ácido nicotínico mostrou os melhores resultados para triacilgliceróis. Os resultados mostraram que os flavonóides podem ser benéficos no tratamento de doença coronariana

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Afferent and efferent connections of the thalamic eminence of the axolotl were determined using the fluorescent compound DiI as a tracer. The thalamic eminence is connected reciprocally with a number of telencephalic and diencephalic areas, particularly with the medial pallium, the amygdala and the preoptic region. Efferent connections are widespread throughout the ipsilateral diencephalon. These findings are discussed in relation to the homology of this nucleus, especially its homologue in agnathan brains.

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Somatic cell nuclei injected into amphibian oocytes enlarge, exchange protein with the surrounding cytoplasm, and actively synthesize RNA for weeks. The message activity of the RNAs synthesized within the oocytes can be detected as new proteins made a few days after the injection of somatic nucleic. The oocyte cytoplasm seems to reprogram the injected nuclei, allowing the expression only of those genes which are normally active in oocytes (De Robertis and Gurdon, 1977). Genes which are unexpressed in somatic cells can be activated by injecting Xenopus laevis somatic nuclei into oocytes of Pleurodeles waltlii (Urodela). The genes that were activated are normally expressed in Xenopus oocytes but not in somatic cells. Conversely, genes which are normally expressed in somatic cells but not in oocytes become inactive after injection into oocytes. We conclude that genes which become inactive during cell differentiation can be reactivated, in the absence of cell division, by normal components of oocyte cytoplasm. These components could turn out to be examples of the "determinants" of egg cytoplasm responsible for nuclear activity in early development.

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