MITOTIC INSTABILITY IN HAPLOPAPPUS: STRUCTURAL AND GENIC CAUSES
MITOTIC INSTABILITY IN HAPLOPAPPUS: STRUCTURAL AND GENIC CAUSES
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Haplopappus 有丝分裂不稳定性：结构和遗传原因
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发表时间：
1985
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通讯作者：
R. C. Jackson
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作者：
R. C. Jackson
有丝分裂不稳定性存在于细柄单胞菌Haplopappus gracilis(Nutt.)Gray和高山毛虫种间杂交种。和H.aureus Gray。后者是染色体数目和DNA含量不同的远缘种间杂交。由于含有野生型基因的染色体片段丢失，种内杂交种表现为部分隐性表型，而种间杂交种由于染色质丢失，在几个形态性状上表现出异常发育模式。这两个杂交种的生长速度较慢，体型较小，总体上比亲本弱。在这两个例子中，这一弱点都与染色质丢失有关，这是由于染色体臂上的细胞壁形成太长而无法在后期正确分离而造成的分裂。这是由于细粒棘豆中非常不平等的易位和种间杂交中基因组大小的差异造成的。在这两个例子中，最初的染色体分裂导致了一个断裂-融合-桥循环，该循环持续到一些BC，即细粒棘豆的后代。可能导致一个断裂-融合-桥梁(BF]3)循环(McClintock，1938、1939、1941)。影响纺锤体长度或取向、着丝粒激活和染色体差异复制的突变可导致单条染色体或整个基因组的丢失。在单胞虫中发现的两个有丝分裂不稳定的例子涉及一个种内杂种中非常不平等的易位和一个种间杂种中纺锤体长度的遗传控制。这两个例子是相关的，因为它们都有一个或多个染色体太长，在有丝分裂后期无法正确分离。材料和方法--细柄单胞菌Haplopappus gracilis(Nutt.)Gray(n=2)和种间杂交种。(n=4)在幼苗早期生长过程中表现出一定的形态异常后，对x.aureus Gray(n=6)进行了有丝分裂不稳定性的分析。在自来水中萌发一年生纤细管藻种子，然后在幼苗长约10 mm后转移到水膨胀的Jiffy-7泥炭颗粒(Jiff9 Products Ltd.，挪威)中。在5%次氯酸钙水溶液中对金色海棠种子进行表面灭菌，然后在无菌蒸馏水中漂洗、发芽或解剖。然后将成熟果实的幼苗或部分发育的胚胎放在用一半强度的Hoagland‘s溶液制成的1%无菌琼脂上，在光照下生长。长到约10毫米的幼苗被转移到水膨胀泥炭颗粒中。泥炭颗粒中的所有幼苗都放置在白色有丝分裂中，有丝分裂不稳定可以定义为核染色体到子核的正常数量和质量分裂的任何偏离。有一些具有遗传系统的生物体，在发育过程中片段、整个染色体或整个基因组被消除，这样的事件在每一代新一代都会重复发生(Lewis和John，1963)。这种调整后的系统不应被称为不稳定--它们是异常的。在有丝分裂正常的生物体中，不稳定可能会导致内部或外部的偏差，表现为一系列异常变化。从杂合子中隐性基因的表达，到某些杂交种中只有一个亲本的完全表型和遗传型表达，这些问题都有。最极端的情况会造成致命的后果。有丝分裂不稳定的原因可以分为两大类--结构和基因，但在一些例子中，两者是相互关联的。产生染色体臂过长以至于被细胞壁形成切断的结构变化可能导致有丝分裂不稳定(Jackson，1985)。这种变化可能是由非常不平等的相互易位、着丝粒周围倒置和中心性移位引起的。由转位元件激活引起的基因诱导的结构重排可以产生这些类型的改变，外加环形和双着丝粒染色体(Jackson，1985)。所有这些更改均已收到，1 1984年10月30日出版，1985年4月8日接受修订。
Mitotic instability was found in an intraspecific hybrid of Haplopappus gracilis (Nutt.) Gray and in an interspecific hybrid of H. arenarius Benth. and H. aureus Gray. The latter cross was between distantly related species with difEerent chromosome numbers and amounts of DNA. The intraspecific hybrid exhibited a partly recessive phenotype due to loss of a chromosome segment containing the wild type locus, and the interspecific hybrid showed abnormal developmental patterns for several morphological characters due to chromatin loss. Both hybrids were slower growing, smaller, and generally weaker than parental types. In both examples, this weakness was correlated with chromatin loss due to cleavage by cell wall formation across chromosome arms too long to separate properly at anaphase. This was caused by a very unequal translocation in H. gracilis and to a disparity in genome sizes in the interspecific hybrid. In both examples, the initial chromosome cleavage resulted in a breakage-fusion-bridge cycle that persisted into some BC, progeny of H. gracilis. may lead to a breakage-fusion-bridge (BF]3) cycle (McClintock, 1938, 1939, 1941). Mutations that affiect spindle length or orientation, centromere activation, and differential chromosome replication can lead to single chromosome or whole genome loss. The two examples of mitotic instability found in Haplopappus involve a very unequal translocation in one intraspecific hybrid and genetic control of spindle length in an interspecific hybrid. The two examples are related in that both have one or more chromosomes too long to properly separate at mitotic anaphase. MATERIALS AND METHODS-Intraspecific hybrids of Haplopappusgracilis (Nutt.) Gray (n = 2) and interspecific hybnds of Haplopappus arenarius Benth. (n = 4) x H. aureus Gray (n= 6) were analyzed for mitotic instability after exhibiting certain morphological aberrations in early seedling growth. Seeds of the annual H. gracilis were germinated in tap water and then transferred to waterexpanded Jiffy-7 peat pellets (Jiff9 Products Ltd., Norway) after the seedlings were ca. 10 mm long. Seeds of H. arenarius x H. aureus were surface-sterilized in an aqueous solution of 5% calcium hypochlorite and then rinsed, germinated, or dissected in sterile distilled water. Seedlings or partially developed embryos from mature fruits were then placed on sterile 1% agar made with half-strength Hoagland's solution and grown under lights. Seedlings that reached a length of ca. 10 mm were transferred to water-expanded peat pellets. All seedlings in peat pellets were placed in white MITOTIC instability may be defined as any deviation from a normal quantitative and qualitative division of nuclear chromosomes into daughter nuclei. There are some organisms with genetic systems in which fragments, whole chromosomes, or entire genomes are eliminated during the course of development, and such events are repeated for each new generation (Lewis and John, 1963). Such adjusted systems should not be referred to as instablethey are anomalous. In organisms with a normal mitosis, instability may lead to internal or external deviations that are manifest in a series of abnormal changes. These range from expression of recessive genes in heterozygotes to the complete phenotypic and genotypic expression of only one parent in certain hybrids. The most extreme cases cause lethality. The causes of mitotic instability can be included under two broad categories-structural and genic, but in some examples the two are interrelated. Structural changes that produce chromosome arms so long that they are cut by cell wall formation can lead to mitotic instability (Jackson, 1985). Such a change could be caused by very unequal reciprocal translocations, pericentric inversions, and centric transpositions. Gene-induced structural rearrangements caused by activation oftranspositional elements could produce these kinds of changes plus ring and dicentric chromosomes (Jackson, 1985). All ofthese changes 1 Received for publication 30 October 1984revision accepted 8 April 1985.