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Biomedical subjects

J J Picard

Publications and source records attributed to J J Picard.

At least 37 records · Page 2Linked to original sources
PubMed1981

Characterization of a new cell line, XL2, obtained from Xenopus laevis and determination of optimal culture conditions.

A new amphibian permanent cell line is described. It is called XL2 and was initiated from Stage 35 tadpoles of Xenopus laevis. The cell line has an epithelioid morphology and most cells can be classified into two populations with respective chromosome modal numbers 36 and 74. Contact inhibition is low. Its growth is vigorous in L15 or MEM medium supplemented with fetal bovine serum. The mean doubling time is 39 hr and the saturation density is 700,000 cells/cm2 at 25 degrees C. The absolute plating efficiency is about 70%. Cell line XL2 is unable to grow in L15 medium containing a macromolecular fraction of fetal bovine serum. Growth is restored if the latter medium is supplemented with 10 micrograms/ml of hypoxanthine. Optimal conditions for the dye exclusion test, for harvesting the cells, and for cloning in petri dishes are described.

Animals↗
PubMed1980

Liver and kidney tumors induced by N-nitroso-dimethylamine in Xenopus borealis (Parker).

N-nitroso-dimethylanine dissolved in aquarium water at a concentration of 400 ppm (1/4 of the LD50/30d) induced malignant tumors in 39 (54.2%) out of 72 young adult animals of the amphibian species Xenopus borealis. The first tumor was detected at 11 weeks, and the average latency was 35.1 weeks. Tumors were located in the liver (32 cholangiocarcinomas and 13 hepatocellular cancers) and the kidney (9 adenocarcinomas and 2 anaplastic cancers). Thirteen animals bore two or more types of tumors. These results demonstrate that a high percentage of tumors can be induced in amphibians by chemical carcinogens if appropriate methods are used.

Adenocarcinoma↗
PubMed1978

Surface changes during development and involution of the cement gland of Xenopus laevis.

The cement gland was studied from stage 17, when the anlage is established, to stage 49, shortly before its disappearance. At early stages, the apical membrane is covered by small microvilli that are more abundant than in the surrounding epiblast cells. Vesicular protrusions along the cell boundaries are also more numerous in the gland cells. When the gland reaches maturity, the apical membranes of gland cells differentiate into two regions. In the cranial, kidney-shaped region, the membranes are very narrow and protrude above the level of cell boundaries. Long and slender villi raise from the surface adjacent to cell boundaries. Apical surfaces in the caudal portion are larger and flattened. Cell boundaries are lined with shorter and thicker surface projections. At these stages, the bordering cells are covered with secretion vesicles. During involution the number of cells is progressively reduced. The area of the caudal portion increases relative to the area of the cranial portion. Apical surfaces become more flattened. Surface projections become much shorter and invade the whole of the apical surface. Bordering cells lose their secretion vesicles and their apical surface becomes ruffled with numerous short wrinkles. The significance of the apical structures and their evolution is discussed.

Animals↗
PubMed1978

Heterotopic gastric mucosa in the epiglottis and rectum.

A case of gastric heteropia of the glossoepiglottic region in a 13-day-old girl is described. In addition to fundic-type mucosa, all main parts of the gastric wall were present. An additional case of gastric heteropia in the rectum was found in a 14-year-old boy. The mucosa was lined with a muscularis mucosae. Adjacent to this ectopia was a large peptic ulcer. Previoisly reported cases of gastric heterotopias are reviewed.

Adolescent↗
PubMed1976

Utrastructure of the cement gland of Xenopus laevis.

To establish a morphological baseline for experimental studies of differentiation using the cement gland as a model, the following observations are added to those on record. The elongated cells of Xenopus laevis cement glands have an internal organization displaying five distinct zones differing in structure and specialized function. The apical zone contains packed secretion vesicles apparently belonging to two different types. The transit zone appears to be devoid of major biosynthetic activity and contains secretion vesicles migrating toward the surface. The zone of biosynthesis is typically organized in concentric regions. The very elongated nucleus lies in the next zone. Finally, the storage zone is characterized by lipid droplets and yolk platelets. Only quantitative differences are observed between cells of young and mature cement glands. Though all cells have the same general organization they may probably be divided into two subtypes according to the structure of their cytoplasm. The epithelial cells surrounding the gland differ according to their position along lateral or basal borders.

Animals↗
PubMed1975

Xenopus laevis cement gland as an experimental model for embryonic differentiation. II. The competence of embryonic cells.

Explants of the blastocoelic roof of Xenopus laevis embryos were incubated for 6 h in Holtfreter solution containing 10 mM ammonium chloride and 10 mM sodium bicarbonate. After this incubation they were transferred for 5 days to Barth's physiological salt solution. Under these conditions the explants underwent differentiation into cement gland tissue. The ability to produce cement gland was highest when explants were dissected from young gastrulae (stage 10). Explants from younger and older embryos displayed much smaller cement glands. There is no difference in the response of ventral or dorsal portions of the blastocoelic roof of stage-10 embryos under these in vitro conditions involving ammonium chloride stimulation. Although the treatment changed the fate of some ectoblastic tissues, it was unable to force endodermal or mesodermal tissues of the blastoporal lip to differentiate into cement gland. The amount of cement gland in the ectoblastic explants varied according to the egg-batch and on the average accounted for 55 percent of the total tissue. The remaining tissue was undifferentiated. Most of this undifferentiated tissue originates from the adjacent layer of the ectoblast. Therefore it may be estimated that the cement gland accounts for 80 to 100 percent of the volume of the competent superficial layer.

Ammonium Chloride↗
PubMed1975

Xenopus laevis cement gland as an experimental model for embryonic differentiation. I. In vitro stimulation of differentiation by ammonium chloride.

Ectoblastic cells explanted from the animal pole of young Xenopus laevis gastrulae have been cultured in vitro. When these cells were cultured for five days in standard salt solutions they formed atypical epidermis. When they were first submitted for 6 h to Holtfreter solution containing ammonium chloride and then transferred for five days in standard Barth's solution they underwent differentiation into typical cement gland tissue. The optimum concentration of ammonium chloride was 10 mM. Below and above this concentration the resulting cement glands had a smaller volume. The optimum duration for the initial stimulation with 10 mM ammonium chloride in Holtfreter solution was 6 h. Shorter stimulation times produced only small cement glands. Longer initial incubations in ammonium chloride resulted in progressive dissociation of the explants. To obtain the best differentiation into cement gland it appeared that the pH of the ammonium chloride solution should be between 7-5 and 7-7. When the stimulation is performed under these optimum conditions the cement gland measured after five days of culture accounts for 80-90 percent of the explanted tissue. This means that all or almost all of the competent superficial layer of the ectoblastic cells underwent differentiation into cement gland. No other differentiated tissue was observed in the explants. The cement gland is a very simple organ containing only one single cell type. The gland obtained under the described in vitro conditions is therefore proposed as an experimental model for biochemical studies on early embryonic differentiation.

Ammonium Chloride↗