Shiokawa K, Kawazoe Y, Nomura H, Miura T, Nakakura N, Horiuchi T, Yamana K
Dev Biol. 1986 Jun;115(2):380-91. doi: 10.1016/0012-1606(86)90257-5.
Recently, we have shown that ammonium salts and amines at an external concentration of 3 mM selectively inhibit rRNA synthesis in Xenopus disaggregated neurula cells. We studied here the change in the amount of ammonia within the embryo and its inhibitory action on the commencement of rRNA synthesis which normally occurs at the blastula stage of development. Ammonia exists at ca. 50 ng/egg (or ca. 3.0 mM at an intra-egg concentration) in the unfertilized egg. This level was maintained during cleavage and then sharply decreased during the blastula stage to the level of ca. 20 ng/embryo (or 1.2 mM) in postblastular stages. Ammonia was extracted from cleavage embryos in a form of ammonium chloride and confirmed to selectively inhibit rRNA synthesis in neurula cells. With authentic ammonium chloride, ammonia was found to be promptly incorporated into cells and to inhibit rRNA synthesis within 1 hr after treatment. In blastula cells, ammonium salts reversibly inhibited the commencement of the synthesis of rRNA, but not hnRNA, 5 S RNA and U1, U2, and U5 snRNAs. The inhibition was at the step of transcription of 40 S pre-rRNA but not the processing or degradation of the processed rRNA. Ammonium salts did not inhibit DNA synthesis, protein synthesis, cell division, and cellular reaggregation. These observations suggest that ammonium ion may be involved in the regulation of the commencement of rRNA synthesis in Xenopus embryogenesis, although it is not yet clear if the ammonium ion exerts its effect directly upon the rDNA transcription system.
最近，我们发现外部浓度为3 mM的铵盐和胺类可选择性抑制非洲爪蟾分散的神经胚细胞中的rRNA合成。我们在此研究了胚胎内氨含量的变化及其对rRNA合成起始的抑制作用，rRNA合成通常发生在发育的囊胚期。未受精卵中的氨含量约为50 ng/卵（或卵内浓度约为3.0 mM）。在卵裂期间该水平保持不变，然后在囊胚期急剧下降至囊胚后期约20 ng/胚胎（或1.2 mM）的水平。氨以氯化铵的形式从卵裂胚胎中提取出来，并证实可选择性抑制神经胚细胞中的rRNA合成。使用纯氯化铵时，发现氨可迅速进入细胞并在处理后1小时内抑制rRNA合成。在囊胚细胞中，铵盐可逆性抑制rRNA合成的起始，但不抑制hnRNA、5 S RNA以及U1、U2和U5 snRNA的合成。这种抑制作用发生在40 S前体rRNA转录步骤，而非加工后的rRNA的加工或降解步骤。铵盐不抑制DNA合成、蛋白质合成、细胞分裂和细胞重聚集。这些观察结果表明，铵离子可能参与非洲爪蟾胚胎发育过程中rRNA合成起始的调控，尽管目前尚不清楚铵离子是否直接作用于rDNA转录系统。
