Electron microscopy of DNA molecules from blastoderm nuclei and yolk granules beneath blastoderm of fertilized and unincubated chicken eggs.

The DNA molecules isolated from the blastoderm nuclei and yolk granules beneath the blastoderm of fertilized and unincubated chicken eggs were observed under electron microscope, using the DNA sample of calf thymus as control. The results showed that both nuclear and yolk DNAs are linear, and their molecules are very similar to those of thymus DNA in shape. Since chromatin was first prepared from blastoderm nuclei and yolk granules respectively and then DNA was isolated from both of chromatin samples, it could be concluded that yolk granules possess both DNA chromatin as nuclei do.

Chromatin and DNA of yolk granules beneath "blastoderm region" of unfertilized chicken egg.

Electron microscopic study shows that the chromatin structure of yolk granules beneath the "blastoderm region" of the unfertilized chicken egg is identical to that of yolk granules beneath the blastoderm of the fertilized and unincubated chicken egg, and both chromatin structures are very similar to those of blastoderm nuclei. Furthermore the molecular shapes of DNA of both yolk granules are also very similar to those of the blastoderm nuclei, being all linear. Based on these observations, we have come to the conclusion that chromatin and DNA widely exist in the yolk when yolk granules have reached their development-specified competence. The results indicate further that the yolk granules are capable of synthesizing DNA, and provide the condition for the interaction of DNA with histones to form chromatin through self-organization.

Electron microscopic studies on the chromatin of blastoderm nuclei and yolk granules beneath blastoderm of fertilized and unincubated chicken eggs.

Chromatin prepared both from the yolk granules beneath the blastoderm and from the nuclei of the blastoderm cells of fertilized and unincubated chicken eggs was examined under electron microscope and its structure was compared. The results indicate that the above two kinds of chromatin fibers seem to have no apparent difference in structural relation and diameter. The electron microscopic appearances of the basic structures of both kinds of chromatin are all "beads-on-a-string"-shaped filaments. After the digestion of chromatin from both raw materials with DNase I, the connecting strings of chromatin fibers were cut off, only the scattered beads could be observed under electron microscope. The diameter of the scattered beads is equal to that of the beads on the chromatin fibers, and most of them are 150 A in diameter.