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At least 793 records · Page 44Linked to original sources
PubMed1987

[Electron microscopy studies of ciliated cells in the larval epidermis of Rana t. temporaria (L.) (Amphibia, Anura)].

Examination of the epidermis of Rana temporaria in various stages of development revealed the presence of densely ciliated cells from the late neurula until shortly before metamorphosis. Unlike the other epidermal cells, these ciliated cells do not divide; once formed, they are constant in number until they disappear. In shape, size, and structure, however, they vary depending on stage of development and on their position in the body. In older larval stages and young tadpoles they are fully differentiated and strongly basophilic. Their function is to improve the hydrodynamic properties of the larval body, and hence ultimately to optimize the energy balance during locomotion.

Animals↗
PubMed1987

Differences in the regulation of messenger RNA for housekeeping and specialized-cell ferritin. A comparison of three distinct ferritin complementary DNAs, the corresponding subunits, and identification of the first processed in amphibia.

The ferritin family is a widespread group of proteins that maintain iron in a soluble form and also protect against the toxic effects of excess iron. The structure and sequence of the proteins are highly conserved. However, the cell-specific features of structure which occur within the same organism indicate cell specificity of gene expression and may be related to variations in types of iron storage, i.e. specialized-cell ferritin (stored iron is for other cell types) versus housekeeping ferritin (stored iron is for intracellular purposes related to normal or stress metabolism); the protein structure may also affect rates of iron turnover. Iron induces ferritin synthesis and accumulation by recruiting stored ferritin mRNA that is efficiently translated in cells specialized for iron storage. For the first time we show the occurrence of three different cDNAs from bullfrog tadpoles, corresponding to three subunits of the protein: H, M, and L. Thus, ferritin can be encoded by at least three different mRNAs and probably three different genes, in contrast to the older idea of two, H and L; the subunits maintain the conserved sequences of known ferritins and have similar predicted masses, 20.5, 20.6, and 19.9 kDa, but have distinct mobilities in denaturing gels. Ferritin subunit expression is cell specific; more of the H and L chain mRNAs are expressed in red cells than in liver. Ferritin expression is regulated by transcription (or mRNA stability) in adult red cells; cellular levels of ferritin mRNA were 20% that of embryonic red cells, and L subunit mRNA increased 2.5 times with excess iron. Ferritin expression is also regulated during translation in adult red cells; iron recruits stored ferritin mRNA, but only during certain stages of red cell maturation, in contrast to embryonic red cells. The developmental differences in ferritin expression are discussed in relation to the shift from specialized-cell ferritin to housekeeping ferritin in red cells of the embryonic versus adult lines.

Amino Acid Sequence↗
PubMed1987

The cephalic glands of Brazilian reptilia and amphibia. IV. Histology of labial, premaxillary, and Duvernoy's glands in the colubrid snake Oxyrhopus trigeminus.

A study of the morphology of the salivary glands of the colubrid snake Oxyrhopus trigeminus showed the following: The acini of supralabial, infralabial, and premaxillary glands are formed by mucous and mucoserous cells; the tubules of Duvernoy's gland are formed by seromucous cells; and mucous cells produce neutral and acid mucosubstances, mucoserous cells secrete neutral and acid mucosubstances and protein, and seromucous cells have neutral mucosubstance and protein secretions.

Animals↗
PubMed1986

Intermediate heterochromatic zones in Triturus (Amphibia: Caudata).

Employment of the C-banding procedure disclosed the presence of slightly stained bands in some chromosome regions of several Triturus species. These regions have been previously described in other organisms as 'grey C-bands'. Possible explanations for the presence of these bands in Triturus karyotypes are discussed.

Animals↗
PubMedDate not supplied

[Aging and limited capacity for division of normal, diploid amphibian fibroblasts in vitro in relation to cell nucleus transplantations in amphibia].

In many experiments Hayflick had proved the limited division capacity of lung fibroblasts derived from different mammalian species, chicken and tortoise. Gurdon transplanted the nuclei of differentiated Xenopus cells into enucleated eggs yielding a complete development of the hybrid individuals. These results arise the question about a reprogramming of cell nuclei concerning their division capacity. On the other hand, amphibian cells may not show any proliferative limit. Thus, primary cultures were established from tadpoles, recently metamorphosed frogs and adult animals, respectively. The latent period of the tissue explants proved to be dependent on donor age. The cell strain I401 showed the characteristic degeneration phenomena after six subcultivations and ceased to proliferate. These results lead to the conclusion that nuclear transplantation into an enucleated egg yields reprogramming of the nucleus, including the reprogramming of the division capacity as much as the biological age of the nucleus.

Animals↗
PubMed1985

Meiosis and spermiogenesis in the testis of Salamandra salamandra (L.) (Amphibia, Urodela).

Meiosis and spermiogenesis in the fire salamander, Salamandra salamandra, take place in an intermediate zone of the testis between the cephal immature and the more caudal mature part. Primary spermatocytes in zytogene and pachytene are characterized by synaptonemal complexes, flattened vesicles at the periphery of the cytoplasm and mitochondria with dilated cristae. Mitochondria in primary spermatocytes during meiosis, in secondary spermatocytes and early spermatids are typically arranged beneath the plasmalemma. Secondary spermatocytes are provided with pro-acrosomal granules, nucleolus-like bodies and complexes of annulate lamellae. Cytoplasmic parts with numerous vesicles seem to become extruded from secondary spermatocytes and spermatids. In testicular lobules containing pachytene spermatocytes the normally fibroblast-like follicle cells transform into glandular Sertoli cells. Already after the second meiotic division of germ cells lobule boundary cells show morphological features of steroid hormone secreting cells.

Animals↗
PubMed1977

[Induction of the mesoderm and primordial germ cells by the endoderm of Pleurodeles waltlii (Amphibia, Urodele): development during gastrulation].

Blastulae ectoderm is combined with dorsal or ventral endoderm from blastulae, gastrulae and early neurulae. In vitro culture reveals the presence of different mesodermal structures whose nature is connected with the endoderm origin site. Primordial germ cells differentiate essentially in the recombinates including ventral endoderm. The inducing capacity of this latter concerning germ cells is maximum at the beginning of gastrulation, then decreases during it and finally disappears at the onset of neurulation.

Age Factors↗