Role of the thyroid in the involution of the mesonephric Malpighian corpuscles in the chick embryo

The mesonephros of the chick embryo normally begins to regress during the second half of embryonic life. Experimental methods, such as adenohypophysis grafting, hypophysectomy or use of antithyroid drugs, which stimulate or depress the thyroid function of the embryo, modified accordingly the regressive processes occurring in the mesonephric Malpighian corpuscles, particularly at the level of the glomerular basement laminae. These results as well as the known sensitivity of the mesonephros to thyroxine and the concordance between the steps of embryonic thyroid development and the mesonephric modifications show that the thyroid normally plays a major determining role in this phenomenon.     

Differentiation of the thyroid in the hypophysectomized chick embryo

The influence of hypophyseal hormones on the normal development of the thyroid gland was investigated by decapitating chick embryos at a time before the hypophysis has begun to form. Thyroids from decapitated embryos were compared with thyroids of normal embryos from shortly after decapitation to the time when the embryo should hatch. The thyroids were examined for ultrastructural differences and for accumulation of thyroglobulin. Thyroxine levels in the blood were also examined. It was concluded that the thyroids in decapitated embryos develop normally up to about 12 days of development, by which time morphogenesis and differentiation of the gland is essentially complete. The rates of thyroid growth and accumulation of thyroglobulin are diminished after 12 days of development. The amount of thyroxine in the blood is decreased by about one-half. Thyroxine was found in the yolk of unincubated eggs at levels sufficient to sustain blood thyroxine levels throughout embryonic development. We conclude that hormones that are synthesized by the embryonic hypophysis affect thyroid development only through their influence on generalized growth and metabolic activity.     

Development of cell-to-cell relationships in the thyroid gland of the chick embryo

Summary Thyroid glands of 7 to 21 day-old chick embryos were examined by electron microscopy using freeze-fracture and thin-section preparations. The primitive follicle lumen first appears between two adjacent epithelial cells in 8 day-old embryos, and is formed in the region of a focal tight junction (macula occludens). The focal tight junction develops into the zonula occludens when the primitive follicle lumen first forms.The zonula occludens is, at first, composed of 4.6 ± 2.45 strands, but with increasing embryonic age the number of strands increases to 5.9 ± 1.41 in 13 day-old, and 8.0 ± 1.75 in 19 day-old embryos.Thyroglobulin stored within the embryonic gland lumina is isolated from the mesenchymal tissue even at the first appearance of these follicle cavities.Well developed gap junctions already occur in the thyroid gland of the 7 day-old embryo, so that an intimate relationship and communication between these cells already exists at the time of their functional differentiation.This study was supported by a grant from the Japan Ministry of Education     

Changes of creatine concentration during development of chick embryo

Changes of creatine concentration during development of chick embryo. Acta physiol. pol., 1985, 36 (3): 208-215. Investigations were carried out on embryos of Star Cross chicken after 6, 8, 10, 12, 14, 16, 18 and 20 days of incubation. It was found that the concentration of total creatine increased from 0.18 to 0.67 mg/g of embryo weight. The increase of creatine concentration at the time of development of the embryo was proportional to the increase in nitrogen concentration, and the share of creatine nitrogen in the pool of total nitrogen was about 1% throughout the whole period of embryonal development and during the first two days after hatching. The amount of creatine in fresh egg and in the yolk sac of the newly hatched chicken was about 1.5 mg. It was estimated that chick embryos during their development synthesized, on the average, 18 mg (6 mMol) of creatine. The course of changes in creatine concentration in the developing chick embryo is very similar to the course of changes in the rate of heat production.     

Development of an embryonic thyroid grafted into a chick embryo

A morphological and physiological study of an embryonic thyroid grafted in a chick embryo showed that it developed according to the endocrine status of the host. Its relative age appreciated at various stages of embryonic life is different from that of a gland developing normally during similar lengths of time.