A quantitative analysis of ovalbumin utilization by the cultured chick embryo and its relationship to growth regulation during development

Rapid clearance of circulating protein by early chicken embryo blood cells

It has been speculated that free amino acids digested from proteins in bird eggs are transported to the circulation for the nourishment of the embryo. In the present study, we found that early chicken embryo protein in the serum might be utilized efficiently as a nutrient. Proteins injected into the blood of embryonic day 3 (E3) embryos were partially degraded and rapidly cleared. The rapid clearance of the injected proteins might be the result of efficient pinocytosis by blood cells, which then efficiently digested the intracellular proteins. An evaluation of the fluorescence intensity of injected fluorescein isothiocyanate-labeled bovine serum albumin (FITC-BSA) indicated that about half was taken up by the blood cells 80 min after injection. About 4 h after injection, most of the FITC-BSA was digested and the products were released into the serum, which implies that circulating blood cells may serve as a digestive system in early chick embryos. However, the endocytic activity of blood cells decreased after E5, and BSA may reside in the circulation with a longer half-life after E5. These results imply that blood cells would serve as a digestive system only in early embryos. In summary, the mechanism revealed here gives the early embryo the ability to make use of protein as a nutrient without prior digestion outside the embryo.

Changes in shell membranes during the development of quail embryos

The shell membrane of an avian egg acts as a bag enclosing albumen and water. At its interface with the albumen, a smooth layer of homogeneous, dense material called the limiting membrane demarcates the shell membrane. The present study aimed to investigate changes in the limiting membrane during development of quail embryos that were grown with or without being turned. Sixty-three percent of the embryos were hatched after the eggs were incubated at 39 C and in 60% humidity with automatic rotation around their long axis and with their equatorial side down, whereas the hatch rate decreased to 24% when the eggs were incubated without being turned. The width of the limiting membrane at the equatorial region of turned eggs gradually decreased from 74 nm on Days 0 to 2 of incubation to 35 nm on Day 10 and thereafter. Conversely, water permeability, measured by evaporation through the shell membrane increased from 4 to 5 nL/mm2 per min on Days 0 to 6, to 9 nL/mm2 per min on Day 12 and thereafter. In stationary eggs, the decrease in the width of the limiting membrane on the lower side of eggs was delayed until Day 8 of incubation. The water permeability of the shell membrane in this group was 51% of that of the membrane on the upper side of eggs on Day 8 of incubation. Forty to forty-four nanometers seemed to be the critical width of the limiting membrane at which high water permeation could occur. It was also shown that the albumen hinders water permeation through the membrane. These results show that (1) the limiting membrane is made thin during the development over the whole surface with egg-turning, possibly through digestion of still unknown agents, and (2) this thinning accelerates the rate of water permeation through the membrane.

Sequence of events in natural infection of Pekin duck embryos with duck hepatitis B virus

The major mode of natural infection of duck hepatitis B virus (DHBV) in Pekin ducks is vertical transmission, with 95 to 100% of the embryos from DHBV-infected dams eventually becoming infected. Maternally transmitted virus is present in large quantities in the yolk of unincubated eggs and is taken up by the embryo during early development. Synthesis of DHBV DNA in the embryo begins at about 6 days of incubation and coincides with the formation of the liver. DHBV DNA synthesis is incomplete, however, until 8 to 10 days of incubation, as shown by comparing the electrophoretic patterns of DHBV-specific nucleic acid species from embryonic livers at successive stages of development. From 8 days of incubation and continuing throughout embryonic development, subviral particles, which resemble viral replication intermediates isolated from infected livers of post-hatch ducklings, appear in the circulation. These particles contain a polymerase activity that utilizes an RNA template to synthesize viral DNA. Our results suggest that certain host functions, which appear during embryonic development, may be required for DHBV replication and assembly. It is possible that in mammals a similar developmental process occurs. The failure to find human hepatitis B virus in the circulation of most babies, born to hepatitis B virus carrier women, in the first few weeks after birth may reflect such a process.

Synthesis of serum proteins by cultures of chick embryo yolk sac endodermal cells

Endodermal cells were isolated from yolk sacs of 3-day chick embryos and cultured for 6 days in Eagle's minimal essential media plus 10% fetal calf serum. During this period cells rapidly lost their ability to synthesize DNA as judged by [3H]thymidine incorporation into DNA. In spite of this loss of DNA synthesis serum protein synthesis and secretion remained at a constant 45% of total protein synthesis and secretion. This was determined by immunoprecipitation of culture media using antibodies directed against embryonic chick serum proteins. Media were also analyzed for the synthesis and secretion of specific serum proteins using polyacrylamide gel electrophoresis. The relative synthesis and secretion of the individual serum proteins followed that previously observed in ovo with the exception of alpha-globulin-a which became undetectable. When culture media were supplemented with ovalbumin or insulin the relative synthesis and secretion of certin specific serum proteins were altered. However, analysis of these same media samples showed that the total amounts of serum protein synthesis and secretion were unaffected.

Serum protein synthesis in the early chick embryo

Isolated yolk-sacs of chick embryos secreted serum proteins when incubated in buffered chick Ringer's solution. The presence of serum transferrin, two embryo-specific alpha-globulins, and a prealbumin were demonstrated by acrylamide gel analysis. Yolk-sacs from embryos explanted at 11-13 somites (40 hr preincubation) and cultured for 48 hr secreted in addition a protein with the mobility of serum albumin. Incubation of yolk-sacs in the presence of radioactive valine indicated that serum proteins were synthesized as early as the primitive streak stage. By incubating isolated yolk-sacs and embryos from 48-hr explants in the presence of radioactive valine, the synthesis of serum proteins was found to be restricted to the yolk-sac at this stage of development. Culturing explants on various nutrient proteins as well as protein starvation medium altered the relative synthesis of several serum proteins. We have proposed that morphological and biochemical changes in embryos resulting from altered nutrition may be mediated by the proteins of the serum.