A Role for Molecular Studies in Unveiling the Pathways for Formation of Rotifer Resting Eggs and Their Survival During Dormancy
A Role for Molecular Studies in Unveiling the Pathways for Formation of Rotifer Resting Eggs and Their Survival During Dormancy
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DOI：
10.1007/978-3-642-12422-8_7
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发表时间：
2010-01-01
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影响因子：
--
通讯作者：
Lubzens, Esther
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文献类型：
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作者：
Denekamp, Nadav Y.;Suga, Koushirou;Lubzens, Esther
轮虫是微小的水生无脊椎动物，主要栖息在大陆水域，环境条件限制了它们的长期生存。休眠形式、滞育胚胎（休眠卵）的形成是一种促进其基因库在不利环境条件下生存的策略。休眠卵是在有性生殖周期中形成的。通常，轮虫表现出周期性孤雌生殖，无性繁殖的雌性（称为无性繁殖雌性）形成二倍体卵（称为无性性卵），从而导致种群快速增长。称为 mixis 的特定环境信号会诱导有性生殖。最近的研究表明，拥挤是腕轮类单角轮虫有性繁殖开始的诱导信号。有性生殖始于减数分裂的开始，导致单倍体雄性的形成，然后形成二倍体休眠卵。轮虫休眠卵在结构上与无性或无性交卵不同，并且可以保持休眠状态数十年。孵化后，随之而来的是新的无性繁殖周期，导致种群增长和特定环境生态位的殖民化。然而，在某些情况下，有性生殖可能在孵化后不久发生。迄今为止，对单角轮虫进行的分子研究很少，并且大多数仅限于单基因研究。最近形成了针对褶皱臂尾轮虫的大规模表达序列标签资源。它们为对该物种雄性形成、休眠卵和休眠的事件进行分子分析提供了重要的平台。已知与其他生物体（例如酵母孢子、卤虫包囊和种子植物）休眠期间的干燥耐受性相关的基因也在休眠卵中被发现，尽管它们在休眠期间不一定完全干燥。未来的研究应该致力于调查这个重要的后生动物模型中与进入和退出休眠相关的过程的调节。
Rotifers are minute aquatic invertebrates inhabiting mainly continental waters with environmental conditions restricting their long-term survival. Formation of dormant forms, diapausing embryos (resting eggs), is a strategy that facilitates their genetic pool survival beyond unfavorable environmental conditions. Resting eggs are formed during the sexual reproductive cycle. Usually, rotifers display cyclic parthenogenesis, with asexually reproducing females (known as amictic females) forming diploid eggs (called amictic eggs) that are responsible for fast population growth. Specific environmental cues known as mixis induce sexual reproduction. Recent studies implicate crowding as the inducing signal for onset of sexual reproduction in brachionid monogonont rotifers. Sexual reproduction starts with the commencement of meiosis leading to the formation of haploid males and followed by the formation of diploid resting eggs. Rotifer resting eggs differ structurally from asexual or amictic eggs and can remain dormant for decades. Following hatching a new cycle of asexual reproduction ensues, leading to population growth and colonization of the specific environmental niche. In some cases, however, sexual reproduction may occur shortly after hatching. Very few molecular studies were performed on monogonont rotifers so far and most were limited to single gene studies. Large scale expressed sequence tags resources were formed recently for the rotifer Brachionus plicatilis. They are providing important platforms for molecular analyses on the events leading to the formation of males, resting eggs and on dormancy in this species. Genes known to be associated with desiccation tolerance during dormancy in other organisms (e.g., yeast spores, Artemia cysts, and seed plants) were also identified in resting eggs, even though they do not necessarily fully desiccate during the dormant period. Future studies should be directed to investigate the regulation of processes associated with the entrance and exit from dormancy, in this important metazoan model.