Genomic exclusion in Tetrahymena thermophila: A cytogenetic and cytofluorimetric study
Genomic exclusion in Tetrahymena thermophila: A cytogenetic and cytofluorimetric study
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嗜热四膜虫的基因组排除：细胞遗传学和细胞荧光研究
DOI：
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发表时间：
1979
期刊：
影响因子：
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通讯作者：
S. K. Shabatura
中科院分区：
文献类型：
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作者：
F. P. Doerder;S. K. Shabatura
基因组排斥是嗜热四膜虫接合的一种异常形式，其中缺陷接合子的基因组从接合子后代的基因型中排除。本文研究衰老克隆A*III和C* 中基因组排斥的细胞遗传学和核质事件。在A*III或C* 与菌株B的杂交中，仅在菌株B细胞中形成有功能的单倍体配子核。在某些情况下，其中一个配子核在迁移配子核转移之前分裂，然后两种产物都进行DNA合成。迁移核转移后，遵循两种可选的细胞遗传学途径。在第一种情况下，接合子分离而没有进一步的微核分裂。该途径在A*III基因组排除中最常见。在接合子中，前配子核经历DNA合成和（推测）着丝粒的核内分离以恢复微核二倍体。每个接合子的旧大核保留下来而不自溶。这类接合子存活下来，并为将来的有性后代提供基因。在第二个细胞遗传学途径中，配子核分裂并形成大核原基，如在正常接合中一样。该途径在C* 基因组排除中更常见。原基的初始DNA含量从单倍体到二倍体不等。在两到三轮DNA合成后，大核的进一步发育停止，原基似乎发生自溶。旧的大核会浓缩，也会发生自溶，就像正常的接合一样。除了罕见的C* exconjugants，其中大核发育完成，anlagen-bearing基因组排斥exconjugants死亡。死亡可能是由非整倍性，时间或自溶信号的接受性错误，或携带anlagenexconjugants无法进食。含原基的接合物在原基和微核数量方面经常是异常的。大多数的异常现象可以解释为在发育信号和核分裂的时间上的假设错误。罕见的接合子，其中配子核分裂，但不产生大核原基也被观察到。在这些情况下，旧的大核浓缩并发生自溶。因此，旧大核的破坏与大核原基的存在无关，需要细胞配对才能启动。
Genomic exclusion is an aberrant form of conjugation of Tetrahymena thermophila in which the genome of a defective conjugant is excluded from the genotype of the exconjugant progeny. This paper is concerned with the cytogenetic and nucleocytoplasmic events of genomic exclusion in senescent clones A*III and C*. In crosses between A*III or C* and strain B, functional, haploid gametic nuclei are formed only in the strain B cell. In some instances one of the gametic nuclei divides prior to transfer of the migratory gametic nucleus, and both products then undergo DNA synthesis. Two alternative cytogenetic pathways are followed after transfer of the migratory nucleus. In the first, the conjugants separate without further micronuclear divisions. This pathway was most common in A*III genomic exclusion. In exconjugants the former gametic nuclei undergo both DNA synthesis and (presumably) intranuclear separation of centromeres to restore micronuclear diploidy. The old macronucleus of each exconjugant is retained without autolysis. This class of exconjugant survives and contributes genes to future sexual progeny. In the second cytogenetic pathway the gametic nuclei divide and macronuclear anlagen are formed, as in normal conjugation. This pathway was more common in C* genomic exclusion. The initial DNA content of the anlagen ranges from haploid to diploid. Following two to three rounds of DNA synthesis, further macronuclear development ceases and the anlagen appear to undergo autolysis. The old macronucleus condenses and also undergoes autolysis, as in normal conjugation. Except for rare C* exconjugants, in which macronuclear development is completed, anlagen-bearing genomic exclusion exconjugants die. Death may be caused by aneuploidy, errors in the timing or receptivity to signals for autolysis, or the inability of anlagen-bearing exconjugants to feed. Anlagenbearing conjugants are frequently abnormal with respect to the number of anlagen and micronuclei. Most of the anomalies can be explained by postulating errors in the timing of both developmental signals and nuclear divisions. Rare conjugants in which gametic nuclei divide but do not give rise to macronuclear anlagen are also observed. In these instances, the old macronuclei condense and undergo autolysis. Destruction of the old macronucleus therefore is independent of the presence of macronuclear anlagen and requires cell pairing in order to be initiated.