A mutation in the chicken resulting in total amelia is described. Genetic analysis indicates that the limbless condition is due to an autosomal recessive gene. In the limbless embryos the apical ectodermal ridge is lacking. However both the pectoral and pelvic girdles as well as the respiratory and excretory systems are normal. In the affected embryos usually the upper beak is shorter than the lower beak.
Metamorphic changes occurred in dark and white Mexican axolotls injected with 3,3',5-triiodo-L-thyronine (Ta) or DL-thyroxine (T4), when exposed at the following ages (in days) after spawning: 3-8, 45, 62, 117, 521-541, 541-571, at 20°C. The dosage of the hormone administered as a single injection varied from 10 pg to 100 pg. Optimum conditions in group 1 proved to be 10 pg T s injected into the perivitelline space of six-day-old embryos which were subsequently released from the jelly to fresh water nine days later at 15 days of' age. After two days in fresh water tissue changes were observed in this order: gills -ventral, middle, dorsal; tailtip; skin; upper eyelid. Ts-treated animals had a shorter latent period than T4 groups. There was heavy mortality in younger animals. Surviving axolotls completed metamorphosis within 25 to 35 days. Embryonic tissues,, therefore, are capable of taking up the hormone and responding after the treatment is terminated, raising doubts as to the obligatory persistence of the hormone. The implications of these observations with regard to the effect of hormone at the molecular level are discussed.In this report evidence will be presented to show that very early in their ontogeny the embryonic tissues of the Mexican axolotl (Siredon m e x i c a n u m ) are capable of taking up exogenous thyroid hormones, especially triiodothyronine, and of responding after the treatment is terminated. In addition, results on differential tissue sensitivity, quantitative aspects of the regression of the susceptible tissues, comparison of responses to thyroxine (T4) and triiodothyronine (TI 1, and the nature of response in different age groups and dark and white strains will be presented.Many investigators have studied various aspects of metamorphosis in the life history of both urodeles and anurans: the majority of such studies have been included in the reviews by Marx ('35), Lynn and Wachowski ('51) and Etkin ('64). It is well established that Mexican axolotl tissues are sensitive to exogenous thyroid hormones and that their own pituitary does not produce TSH to release endogenous thyroid hormones even though the thyroid is filled with colloid (Lynn and Wachowski, '51). Very little evidence exists in the literature as to how early the tissues of the axolotl or any other urodeles become sensitive to exogenous hormones. Uhlenhuth ('21) immersed Ambystoma maculatum embryos (first 4 visceral arches formed) in iodine-free water containing 1 mg% Bayer's iodothyrine for 20 days. Then he increased the concentration to 10 mg% J. EXP. ZOOL., 160: 137-146.for seven days more. At the end of a total period of 27 days the gills as well as fin of the tail were greatly atrophied. EXPERIMENTALIn the experiments reported below as many standardized conditions as possible were maintained and the animals were neither thyroidectomized nor hypophysectomized as they were already genetically hypophysectomized with respect to thyroid function (Blount and Blount, '47; Blount.' 5 0 ) . Treatment 3,5,3'-triiodo-~-thyro...
The fungicides ethylenebis [dithiocarbamic acid] (nabam) and ethylenebis [dithiocarbamato] manganese (maneb) were dissolved in a modified Holtfreter's solution at concentrations of 0.1–5 ppm. Thirty to 60 yolk‐plug Xenopus laevis embryos were placed for 1–10 days in 200 ml of different concentrations of the fungicide solution. Treated and control (Holtfreter's only) embryos were fixed in Bouin's fluid or formalin for light microscopy, and in glutaraldehyde‐formaldehyde for electron microscopy. Gross morphological and histological observations were made. The first changes observed in experimental embryos was a slight growth retardation and a transient absence or reduction in melanogenesis in the eye and on the rest of the body. The tail was shortened and the notochord had a distinct waviness. Animals in higher concentrations were unable to swim as well as controls. Histological examination, both light and electron microscopic, showed a general decrease in melanin content of the melanosomes in the pigmented retina. The notochord was increased in diameter; in sagittal sections the foldings were obvious. These results indicate that minute doses of these commonly used fungicides are harmful to the normal development of amphibian embryos.
Groups of 30 Xenopus laevis embryos, at "tail-bud" stage (Nieukoop-Faber stages 22-24) were exposed to 0.1-2 ppm concentrations of various pesticides for 1 to 10 days. The pesticides used were chloranil and dichlone (both are fungicidal and herbicidal); diquat (herbicide); and nabam (fungicide). The parameters examined were mortality, gross morphology, histology, and behavior. Chloranil (1.25 to 1.75 ppm) treated embryos showed abnormalities of the otolith, optic cup, and general pigmentation. Their movement was sporadically convulsive and they were unable to maintain proper balance. Dichlone (0.1 to 0.15 ppm) disrupted the development of the cephalic end of the embryo. Many of these embryos developed a slightly retarded trunk and tail only. These headless embryos lived for a time and were relatively lethargic. Diquat (0.75 to 2.0 ppm) administration reduced body size and pigmentation, and altered body shape. When embryos were treated with both 1.0 ppm of diquat and 2.0 ppm of nabam the integrity of myomeres and myocommata of the musculature was disrupted. The histological bases of these morphological and behavioral changes are discussed.
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