Smothers J F, Madireddi M T, Warner F D, Allis C D
Department of Biology, University of Rochester, New York 14627, USA.
J Eukaryot Microbiol. 1997 Mar-Apr;44(2):79-88. doi: 10.1111/j.1550-7408.1997.tb05942.x.
Programmed DNA rearrangements, including DNA degradation, characterize the development of the soma from the germline in a number of developmental systems. Pdd1p (programmed DNA degradation 1 protein), a development-specific polypeptide in Tetrahymena, is enriched in developing macronuclei (anlagen) and has been implicated in DNA elimination and nucleolar biogenesis. Here, immunocytochemistry and fluorescent in situ hybridization (FISH) were employed to follow Pdd1p and two nucleolar markers (Nopp52 and rDNA) during macronuclear development. Both Pdd1p and Nopp52 localize to subnuclear structures, each of which resemble nucleoli. However, while true nucleoli form and persist during development, Pdd1p-positive structures are only present for a brief period of macronuclear differentiation. Accordingly, two distinct organelles can be recognized in anlagen: (1) Pdd1p-positive structures, which lack Nopp52 and rDNA, and (2) developing nucleoli which contain rDNA and Nopp52 but lack Pdd1p. Taken together with recent data corroborating Pdd1p's role in DNA elimination, we favor the hypothesis that Pdd1p structures are unique, short-lived organelles, likely to function in programmed DNA degradation and not in nucleolar biogenesis.
程序性DNA重排，包括DNA降解，是许多发育系统中生殖细胞系向体细胞发育过程的特征。Pdd1p（程序性DNA降解1蛋白）是嗜热四膜虫中一种与发育相关的多肽，在发育中的大核（原基）中富集，并且与DNA消除和核仁生物发生有关。在这里，我们采用免疫细胞化学和荧光原位杂交（FISH）技术，追踪大核发育过程中的Pdd1p以及两种核仁标记物（Nopp52和rDNA）。Pdd1p和Nopp52都定位于亚核结构，每个亚核结构都类似于核仁。然而，虽然真正的核仁在发育过程中形成并持续存在，但Pdd1p阳性结构仅在大核分化的短暂时期出现。因此，在原基中可以识别出两种不同的细胞器：（1）缺乏Nopp52和rDNA的Pdd1p阳性结构，以及（2）含有rDNA和Nopp52但缺乏Pdd1p的正在发育的核仁。结合最近证实Pdd1p在DNA消除中作用的数据，我们支持这样的假说，即Pdd1p结构是独特的、寿命短暂的细胞器，可能在程序性DNA降解中发挥作用，而不是在核仁生物发生中发挥作用。
