Vascular regression during the formation of the free digits in the avian limb bud: a comparative study in chick and duck embryos

The pattern and structure of the blood vessels of the interdigital spaces of the leg bud have been studied by means of Indian ink injections and transmission electron microscopy in the chick and duck embryos. The results show that in the chick the interdigital necrotic process responsible for the freeing of the digits is followed by regression of the blood vessels. In the webbed foot of the duck, the interdigital necrotic processes are not followed by vascular regression. Transmission electron microscopic studies show that both in the chick and in the duck, interdigital blood vessels are immature structures lacking basal lamina. Dead cells of presumably endothelial origin were detected in the lumen of the regressing blood vessels of the chick but not in the duck. However, the intensity of this cell death process does not appear to be high enough to account by itself for the disappearance of the interdigital blood vessels. The possible relationships between interdigital mesenchymal cell death and vascular regression are discussed.

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Cell death and the development of limb form and skeletal pattern in normal and wingless (ws) chick embryos

Development ◽

10.1242/dev.30.3.753 ◽

1973 ◽

Vol 30 (3) ◽

pp. 753-772

Author(s):

J. R. Hinchliffe ◽

D. A. Ede

Keyword(s):

Cell Death ◽

Phenotypic Expression ◽

Mesenchymal Cell ◽

Limb Bud ◽

Death Process ◽

Electron Microscopic ◽

Wide Range ◽

Skeletal Pattern ◽

Autoradiographic Analysis ◽

Mutant Phenotypes

The wingless condition resulting from the action of the sex-linked wingless (ws) gene arises from the precocious appearance of cell death in the anterior necrotic zone (ANZ) of the forelimb-bud at stage 19 (3 days) and its progressive extension beyond its normal area during stages 20–23. A similar though less pronounced effect occurs in the hindlimb-bud. Although some wingless hindlimb-buds are normal, others are affected by the precocious appearance of cell death in the ANZ. The ws wingless mutant resembles the different wingless mutant investigated by Zwilling (1956) in that the apical ectodermal ridge (AER) is absent in most ws wing-buds. AER absence could be due to ws mesenchymal cell death interfering with the production of apical ectodermal maintenance factor (AEMF), which Zwilling claims is necessary to maintain the AER which plays an essential role in inducing limb outgrowth. Wingless mutant phenotypes range from birds with rudimentary wings and normal legs through a modal type with forelimbs absent and hindlimbs normal to wingless and legless forms showing a high degree of expressivity. Individual wingless embryos vary in the degree to which the precocious ANZ appearing at 3 days is extended into the limb-bud and the wide range of wingless phenotypic expression is attributed to this variation. Electron microscopic and histochemical analysis of the cell death process in wingless wing-buds revealed the presence of both isolated dead cells and macrophages, which contained intense acid phosphatase activity. These findings are interpreted as showing that isolated dead cells are ingested by neighbouring mesenchymal cells which thus become transformed into macrophages, first ingesting and then digesting further dead cells. A study was made of the origin of the anomalous hindlimb condition, including absence or reduction of the tibia and digits, characteristic of severely affected wingless embryos. Autoradiographic analysis of the pattern of 35SO4 uptake revealed that at stage 24/5 (4½ days) wingless hindlimb-buds which were smaller than normal had a normal prospective fibula region, but that the prospective tibia region was small or absent. Thus the effect of a precocious hindlimb ANZ at stages 19–22 is to reduce or delete the pre-axial prospective tibia at stage 24/5.

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Radial mass analysis of unstained STEM images of molluscan hemocyanins

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100161618 ◽

1990 ◽

Vol 48 (3) ◽

pp. 810-811

Author(s):

M.G. Hamilton ◽

T.T. Herskovits ◽

J.S. Wall

Keyword(s):

Image Analysis ◽

Hollow Cylinder ◽

Electron Micrographs ◽

Side View ◽

Mass Analysis ◽

Mass Measurements ◽

Electron Microscopic ◽

Transmission Electron ◽

Transmission Electron Microscopic ◽

Microscopic Studies

The hemocyanins of molluscs are aggregates of a cylindrical decameric subparticle that assembles into di-, tri-, tetra-, penta-, and larger multi-decameric particles with masses that are multiples of the 4.4 Md decamer. Electron micrographs of these hemocyanins typically show the particles with two profiles: circular representing the cylinder viewed from the end and rectangular representing the side-view of the hollow cylinder.The model proposed by Mellema and Klug from image analysis of a didecameric hemocyanin with the two decamers facing one another with collar (closed) ends outward fits the appearance of side-views of the negatively-stained cylinders. These authors also suggested that there might be caps at the ends. In one of a series of transmission electron microscopic studies of molluscan hemocyanins, Siezen and Van Bruggen supported the Mellema-Klug model, but stated that they had never observed a cap component. With STEM we have tested the end cap hypothesis by direct mass measurements across the end-views of unstained particles.

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