ULTRASTRUCTURAL PATTERNS OF RNA-SYNTHESIS DURING EARLY EMBRYOGENESIS OF DROSOPHILA-MELANOGASTER
ULTRASTRUCTURAL PATTERNS OF RNA-SYNTHESIS DURING EARLY EMBRYOGENESIS OF DROSOPHILA-MELANOGASTER
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DOI：
10.1016/0092-8674(76)90014-3
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发表时间：
1976-01-01
期刊：
影响因子：
64.5
通讯作者：
MILLER, OL
中科院分区：
文献类型：
--
作者：
MCKNIGHT, SL;MILLER, OL
染色质是在早期胚胎发生过程中从黑腹果蝇中获得的，并通过透射电镜进行检查。在合胞体发育的进展阶段扩散的核内容物仅显示出低水平的非核仁模板活性，并且观察到非常少的长度延伸超过2μm的RNP[核糖核蛋白]原纤维梯度。在细胞胚层阶段，新激活的核仁基因出现在第一个真正细胞周期的早期部分。不完全r[核糖体]RNP梯度长度的变化表明每个rRNA基因的激活是独立控制的。所有 rRNA 位点，无论具有完全梯度还是不完全梯度，每单位长度都表现出高密度的新生转录物，这表明染色质转录速率，而不是 RNA 聚合酶 I 库大小，限制了单个基因上的 rRNA 合成。在此阶段，不超过一半的 rRNA 基因被去抑制，表明总 rRNA 合成受激活基因数量的调节。覆盖高达 8 μm 基因组的非核仁 RNP 原纤维梯度也是在细胞胚盘阶段首次观察到的。大多数这些梯度与合体生长期间首次出现的短梯度不同，转录 RNA 聚合酶的密度较低。
Chromatin was obtained from D. melanogaster during early embryogenesis and examined by transmission EM. Nuclear contents spread at progressive stages of syncytial development show a low level of only non-nucleolar template activity, and very few RNP [ribonucleoprotein] fibril gradients extending over 2 .mu.m in length are observed. At the cellular blastoderm stage, newly activated nucleolar genes appear during the early portion of the 1st true cell cycle. Variation in the lengths of incomplete r[ribosomal]RNP gradients indicates that the activation of each rRNA gene is independently controlled. All rRNA loci whether having complete or incomplete gradients, exhibit high densities of nascent transcripts per unit length, suggesting that the rate of chromatin transcription, rather than the RNA polymerase I pool size, limits rRNA synthesis on individual genes. No more than half the rRNA genes are derepressed at this stage, indicating that total rRNA synthesis is regulated by the number of genes activated. Non-nucleolar RNP fibril gradients covering up to 8 .mu.m of genome are also first observed at the cellular blastoderm stage. Most of these gradients are differentiated from the short gradients first seen during synctial growth by a lower density of transcribing RNA polymerases.