真菌凋亡.docx

1、真菌凋亡真菌凋亡Developmentally regulated fungal apoptosisReproductionSuicidal cell death has very different roles in different biological systems. The main role of apoptosis in mammals is regulation of normal development, although it is also associated with various other processes, including adaptive respo

2、nses of cells to stress and elimination of pathogens. In fungi, apoptotic cell death is more tightly connected to stress adaptation, while involvement in development is less general and is mainly associated with various aspects of fungal reproduction and aging. We will first review the evidence conn

3、ecting apoptosis with fungal development, particularly during reproduction and aging.真菌细胞凋亡的发育调控繁殖自杀式的细胞死亡在不同的生物系统中有非常不同的作用。细胞凋亡在哺乳动物的主要作用是调控正常发育，虽然它也与各种其他过程相关联，包括细胞对胁迫的适应反应和消灭病原体。在真菌中，细胞凋亡更是与胁迫调适紧密联系，同时一般较少参与生长，而主要与霉菌的繁殖和衰老各个方面相关。我们首先回顾连接细胞凋亡与真菌的生长，特别是在生殖和衰老的迹象。Fungi are capable of sexual (meiotic)

4、 and asexual (mitotic) reproduction. While most species can reproduce sexually, some seem to have lost the ability to mate and are considered asexual (traditionally classified as Deuteromycetes). When mating is possible, it can be of two basic types: homothallic species (capable of self-fertilizatio

5、n) and heterothallic species (non-self-fertilizing). Reproduction in heterothallic species isinitiated by pheromones, which trigger the fusion of hyphae from sexually compatible strains. In S. cerevisiae, there are two mating types termed a and . Cells of each mating type produce and secrete either

6、a or factors (pheromones), which trigger mating in cells of the opposite mating type. Severin & Hyman (2002) showed that in the absence of an appropriate mating partner, exposure of cells to pheromones of the opposite mating type leads to ROS accumulation, DNA degradation and cell death. As might be

7、 expected, deletion of STE20 kinase (a key enzyme in the pheromone-induced MAP kinase signal cascade) prevented this pheromone-induced cell death. The authors further demonstrated ROS-associated celldeath in cell populations, which was in opposite correlation to mating success. These findings were t

8、aken as evidence for the possible occurrence of apoptotic cell death during unsuccessful mating in natural yeast populations. It should be noted, however, that pheromone-induced cell death was observed at pheromone concentrations that were 10-fold higher than physiological concentrations; no cell de

9、ath was induced by 10-fold lower (physiological) concentrations, which were sufficient for shmoo induction.真菌能进行有性（减数分裂）和无性（有丝分裂）生殖。尽管大多数物种可以有性生殖，但是有些物种似乎已经失去了交配的能力，被认为是无性的（传统上归类为半知菌纲）。当可以交配时，也可能有两种基本类型：同宗配合物种/雌雄同株物种（能够自体受精）和异宗配合物种/雌雄异株物种（不能自体受精）。异宗配合物种的生殖是由信息素触发相容的两性菌株菌丝融合开始。在酿酒酵母中，有两种交配型称为a型和型。每个交

10、配型细胞产生和分泌a或因子（信息素），从而启动相反交配型细胞的交配。Severin & Hyman (2002) 表明，在不存在适当的交配伴侣时，细胞暴露于相反交配型的信息素中会导致ROS的积累，DNA降解和细胞死亡。正如预期的那样，删除STE20激酶（由信息素诱导的MAP激酶信号通路的关键酶）可以抑制这种信息素诱导的细胞死亡。作者进一步证明细胞群中细胞死亡与活性氧相关，这与交配成功成反相关。在天然酵母种群不成功配合的时候，这些调查结果提供了细胞凋亡可能发生的证据。然而，应当指出的是信息素诱导的细胞死亡检测到的信息素浓度高于生理浓度10倍；无细胞死亡的信息素诱导低于生理浓度10倍，这足以产生s

11、hmoo效应。In filamentous fungi, vegetative hyphae commonly fuse. These hyphal fusions occur during colony formation as well as between hyphae of different strains as part of parasexual reproduction (Saupe, 2000; Glass & Kaneko, 2003; Glass & Dementhon, 2006). The fusion between hyphae from different st

12、rains forms a heterokaryon, a situation in which cells contain nuclei of different genetic backgrounds. Fungi have evolved specific heterokaryon-incompatibility (HI) loci, which determine hyphal-fusion compatibility (Leslie & Zeller, 1996; Glass et al., 2000). Hyphae must be vegetatively compatible

13、with each other in order to sustain the heterokaryon. When they are incompatible, the HI genes activate a rapid, localized cell-death response, which specifically kills the fusion cell (Glass & Kaneko, 2003). In many ways, HI resembles the well-known hypersensitive response (HR) in plants, during wh

14、ich localized apoptotic-like cell death prevents pathogen spreading (Lam et al., 2001). Both HI and HR are accompanied by classical apoptotic markers and have been widely studied (del Pozo & Lam, 1998; Jacobson et al., 1998; Glass et al., 2000; Saupe, 2000; Marek et al., 2003; Glass & Dementhon, 200

15、6; Paoletti & Clave, 2007; Williams & Dickman, 2008). During HI, the fusion hyphae undergo a series of apoptosis-associated morphological changes, including cytoplasm condensation, vacuolization and shrinkage of the plasma membrane (Glass & Kaneko, 2003; Marek et al., 2003; Glass & Dementhon, 2006).

16、 Nuclear fragmentation and positive TUNEL staining have also been reported. The widespread occurrence and high number of HI loci in filamentous fungi argues for their importance. Unlike the case of yeast pheromones, apoptosis is a general phenomenon of HI and occurs naturally.Therefore, HI demonstra

17、tes an important process in which apoptosis plays a major role.丝状真菌的营养菌丝通常可以融合。准性生殖过程中，这些菌丝在菌落形成以及不同菌株的菌丝之间发生融合 (Saupe, 2000; Glass & Kaneko, 2003; Glass & Dementhon, 2006)。来自不同菌株菌丝之间的融合形成异核体，这时在细胞中就含有不同遗传背景的细胞核。真菌中含有特定的异核体不亲和（HI）位点，这个位点可以决定菌丝融合的兼容性(Leslie & Zeller, 1996; Glass et al., 2000)。菌丝必须彼此有

18、生长的兼容性，以便维持该异核体。当他们不兼容，HI基因激活一个快速的、局部细胞死亡反应，这个反应特异性杀死融合细胞(Glass & Kaneko, 2003)。在许多方面，HI类似于植物中众所周知的过敏反应（HR），即为防止病原体传播植物局部凋亡样细胞死亡(Lam et al., 2001)。HI和HR都伴随着传统的凋亡标志物，并已被广泛研究(del Pozo & Lam, 1998; Jacobson et al., 1998; Glass et al., 2000; Saupe, 2000; Marek et al., 2003; Glass & Dementhon, 2006; Paol

19、etti & Clave, 2007; Williams & Dickman, 2008)。在HI中，融合菌丝经过一系列的细胞凋亡相关的形态学改变，包括细胞质膜的细胞质凝聚，空泡形成/液泡化和收缩(Glass & Kaneko, 2003; Marek et al., 2003; Glass & Dementhon, 2006)。核碎裂和正TUNEL染色的情况也有报道。广泛出现且大量的在丝状真菌中HI位点证明了它们的重要性。与酵母信息素的情况不同，HI的细胞凋亡是一个普遍现象，很自然会发生。因此，HI演示了一个重要过程，在这个过程中细胞凋亡中起主要作用。Apoptotic-like cell

20、death has been associated with spore formation, both sexual and asexual (conidia). In some homothallic species, the immature asci contain eight ascospores, but four of them die during maturation, resulting in four-spore asci. Studies in Coniochaete tetrasperma showed that PCD occurs during spore mat

21、uration, eliminating four of the eight ascospores (Raju & Perkins, 2000). Cytological markers of apoptosis were observed in meiotic mutants of Coprinopsis cinereus (syn. Coprinus cinereus). In these mutants, the nuclei in immature basidiospores arrested after meiotic metaphase I and then underwent a

22、poptotic-like cell death (Lu et al., 2003). Unlike in C. tetrasperma, in which apoptosis occurs during normal development of the wildtype spores, here this process served to eliminate mutant spores. In P. anserina, deletion of the two metacaspase genes caused defects in ascospore formation (Hamann e

23、t al., 2007). Overexpression of the anti-apoptotic Bcl-2 gene in Colletotrichum gloeosporioides caused a sharp increase in conidial production (Barhoom & Sharon, 2007). These last two examples, although circumstantial, suggest that changes in the regulation of apoptosis can affect sexual and asexual

24、 sporulation. In Aspergillus nidulans, apoptotic markers and induction of caspase activity were observed during sporulation (Thrane et al., 2004). Caspase activity was shown by hydrolysis of substrates specific for caspase-3- and -8-like activities. These activities were repressed by the caspase- 3-

25、 and -8-specific irreversible peptide inhibitors, but were not affected by the nonspecific inhibitor E-64. Aspergillus nidulans extract contained two proteins that revealed caspase-like activity: one of them degraded both caspase-3-and -8-specific substrates, whereas the other only degraded the casp

26、ase-8 substrate. Two metacaspases and a single poly-ADP ribose polymerase (PARP)-like protein were identified in A. nidulans. The PARP-like protein was detected in mycelia until the start of conidial formation, and it was then degraded along with increased caspase activity (Thrane et al., 2004).凋亡式细

27、胞死亡与孢子形成以及有性和无性（分生孢子）有关。一些同宗配合的物种成熟子囊含有8个子囊孢子，但在成熟过程中4个死亡，形成四子囊孢子。对四子囊锥毛壳菌（Coniochaete tetrasperma）的研究表明细胞程序性死亡在抱子成熟过程中发生,用来移除4个子囊抱子 (Raju & Perkins, 2000)。在担子菌灰盖鬼伞(CoprinoPsiscinoreus)突变体中观察到细胞凋亡的细胞学标记物。在这些突变体中，一些未成熟的但包子的细胞核在减数分裂I中期停滞然后遭遇凋亡式细胞死亡(Lu et al., 2003)。不像锥毛壳菌野生型孢子在正常发育过程中发生凋亡，这个过程先得消除突变体的

28、孢子。在鹅绒委陵菜，缺失两个metacaspase（半胱氨酸蛋白酶）基因会引起子囊孢子形成中的缺失(Hamann et al., 2007)。炭疽病菌的抗凋亡Bcl-2基因的过量表达导致了产孢量的急剧增加(Barhoom & Sharon, 2007)。这两个例子，虽然间接，但是也表明了改变细胞凋亡的调控会影响有性和无性孢子。在构巢曲霉的芽孢形成过程中观察到细胞凋亡标志物和caspase（细胞凋亡蛋白酶）活性的感应（Thrane et al., 2004)）。底物的水解表明了Caspase的活性，特别是 Caspase 3和8式的活性。这些活性被Caspase 3和8特定的不可逆肽酶抑制剂抑制

29、，但没有受到非特异性抑制剂E-64的影响。构巢曲霉提取物含有两种显示Caspase 样活性的蛋白质：一种分解caspase-3和-8特异性的底物，而另一种只分解caspase-8的底物。在构巢曲霉中鉴定了两个metacaspases和一个单一的多聚ADP核糖聚合酶（PARP）样蛋白。直到分生孢子形成开始才在菌丝体中检测到PARP样蛋白，然后其将随着胱天蛋白酶（Caspase）活性的增加而分解/降低 (Thrane et al., 2004)。These examples show the involvement of apoptosis in fungal reproduction. It c

30、an occur during both meiotic and mitotic spore formation, during normal development and in cases of abnormalities, in which apoptosis might serve as a control mechanism by eliminating the genetically damaged spores. In these cases, apoptosis appears to be closely associated with the cell cycle and m

31、ight be triggered by improper regulation of cell-cycle progression (Madeo et al., 1997; Lu et al., 2003).这些例子表明了真菌繁殖中细胞凋亡的参与。它可以在减数分裂和有丝分裂的孢子形成中发生；也可以在正常和异常情况下发生，作为消除基因损伤孢子的控制机制。在这些情况下，细胞凋亡似乎与细胞周期紧密联系，并被细胞周期进程的不当调节触发(Madeo et al., 1997; Lu et al., 2003)。AgingAging is a process of progressive decline

32、 in the ability to withstand stress, damage and disease. In multicellular organisms, apoptosis has been documented as an anti-aging mechanism. Apoptosis eliminates damaged cells by the coordinated activity of gene products that regulate cell death and induce cell proliferation, so that the old cells

33、 are replaced. ROS-induced cell damage is a major process in aging and there is a correlation between extended life span and increased oxidative resistance (Lorin et al., 2006). Saccharomyces cerevisiae and P. anserina are two model organisms that have been used to study aging. In S. cerevisiae, cells bud a limited number of times, produci