The Structure of the Yolk of the Hen's Egg as Studied by Electron Microscopy

Abstract

A description of the fine structure of the yolk of the unincubated hen's egg has becn providcd, which will serve as a basis for further studies on yolk digestion. The gross components of the yolk (that is, free-floating lipid drops, ycllow and white yolk spheres together with their enclosed lipid subdroplcts, and aqueous protein fluid) could be recognized by phasc contrast and low power electron microscopy. The majority of the lipid drops, whether free floating or enclosed within yolk spheres, were composed of particles about 30 to 60 A in diameter. The protein component of thc yolk was found to consist of round profiles about 250 A in diameter. The surfaces of the yolk spheres were of three types, and it is difficult to decide which represents the true structure although reasons are given for believing that yolk spheres are not normally cncloscd by membranes identical with cell membranes.

The Effect of Dietary Cyclopropene Fatty Acids on the Structure of New-Laid and Stored Hens' Eggs: An Optical and Electron Microscope Study

“…This material (Fig. 2), identified as coming from the latebra, always had the typical structure of white yolk as reported by Riddle (1911), Romanoff and Romanoff (1949), and Bellairs (1961). Samples from the rest of the yolk were always typical of yellow yolk (Fig.…”

“…2 and 3), have long been known to occur in the hen's egg. It has generally been accepted that the yolk is made up of concentric and alternate layers of yellow and white yolk laid down around the elongated latebra (see Riddle 1911;Romanoff and Romanoff 1949;and Bellairs 1961); that the latebra, opening into the nucleus of Pander beneath the blastodisc of the unfertilized egg, also contains white yolk; and that the layers of white yolk are deposited during An optical micrograph of part of a specimen grid has been superimposed on an optical micrograph of yellow yolk (same magnification) to indicate the difficulties associated with the electron microscopy of this material. The small amount of material which can be photographed on a plate (6·5 X 9·0 em) in the microscope at a magnification of X 5,000 is judged if the present magnification is increased 12·5 times.…”

“…These structures have been elucidated further by electron microscopy (Bellairs 1961;Bellairs, Harkness, and Harkness 1963;Bain and Hall 1969;Jensen 1969). The investigations of Press (1964), Bellairs (1965Bellairs ( , 1967, , and provided a background to the development of the vitelline membrane in the ovary.…”

Dehydration induced interactions of egg yolk lipoproteins and low molecular weight carbohydrates

“…Abraham et al (1960) isolated the lowdensity lipoproteins from both egg yolk and hen serum and found they contained galactose, mannose, glucosamine, and sialic acid as the only carbohydrate constituents.. Using electron microscopy Bellairs (1961) found the lipid drops and the yolk sphere subdroplets to be about 2n in diameter and to contain, in turn, small dense particles from 30 to 60 in diameter. She found the continuous phase of yolk to contain small spherical particles about 250 A° in diameter.…”

“…Burley and Cook (1961), as previously mentioned, isolated yolk granules (as described by Romanoff and Romanoff,19^9) and found that they contained the lipovitellins, phosvitin, and a smaller amount of low-density lipoprotein. Wallace (1963) reports that Colvin and Cook believe these granules to be the lipid drops and yolk sphere subdroplets of Bellairs (1961). However, since Bellairs (1961) apparently found the yolk sphere subdrop lets to be similar to the free-floating lipid drops, and since Burley and Cook (1961) reported their sedimented granules were free of contaminating yolk spheres (which they called globules), there appears to be some confusion as to which proteins or lipoproteins are found in each of the various microscopic structures.…”