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

Chromatln 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 in diameter.     

鸡胚细胞核和胚下卵黄颗粒染色质的电子显微镜观察

本文从受精未孵育鸡蛋的胚下卵黄颗粒和胚细胞核,提取染色质进行电子显微镜观察,对其结构作了比较.实验结果表明,卵黄颗粒的染色质纤维与胚细胞核的染色质纤维,无论在形态结构和纤维粗细都无明显差别,其基本结构都呈串珠状. 两种材料提取的染色质,用DNase I消化后,在电子显微镜下只见散在的珠粒,纤维上珠粒间的DNA连丝被切断.珠粒的大小与染色质纤维上的珠粒大小相等,大多数为150埃;这些珠粒,由DNA连接成串珠状结构.     

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 ehromatin 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 and chromatin as nuclei do.     

未受精鸡蛋表层卵黄颗粒的染色质和DNA

本文通过电子显微镜的研究,证明未受精鸡蛋表层卵黄颗粒的染色质同受精未孵育鸡蛋的胚下表层卵黄颗粒的染色质一样,都与核染色质的基本结构相类似;其DNA的分子形态,也同受精未孵育鸡蛋的胚下表层卵黄颗粒一样,都与核的DNA相类似,同为线型DNA。根据这些观察,说明染色质和DNA在一定部位和发育时相的卵黄颗粒中,是广泛存在的。实验结果还进一步指出,卵黄颗粒具有就地合成DNA的能力,而且卵黄颗粒中的DNA可能与组蛋白结合,通过白组织构成染色质。     

鸡胚细胞核和胚下卵黄颗粒DNA分子的电子显微镜观察

本文报道以纯度约为99％小牛胸腺DNA的分子形态作对照,对鸡胚细胞核和胚下卵黄颗粒的DNA分子进行了电子显微镜观察。结果表明,无论是胚细胞核和胚下卵黄颗粒的DNA,都是线型DNA,其分子形态都与小牛胸腺DNA相类似。因为从胚细胞核和胚下卵黄颗粒都先提取染色质,然后从染色质再提取DNA,这样在确定胚下卵黄颗粒中存在着DNA的同时,也证明了其染色质存在的这一事实。