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Embryonic development and a quantitative model of programmed DNA elimination in Mesocyclops edax (S. A. Forbes, 1891) (Copepoda: Cyclopoida)
Journal of Crustacean Biology ( IF 1.1 ) Pub Date : 2016-09-06 , DOI: 10.1163/1937240x-00002473
Michelle K Clower 1 , Ashton S Holub 2 , Rebecca T Smith 3 , Grace A Wyngaard 2
Affiliation  

The highly programmed fragmentation of chromosomes and elimination of large amounts of nuclear DNA from the presomatic cell lineages (i.e., chromatin diminution), occurs in the embryos of the freshwater zooplankton Mesocyclops edax (S. A. Forbes, 1891) (Crustacea: Copepoda). The somatic genome is reorganized and reduced to a size five times smaller even though the germline genome remains intact. We present the first comprehensive, quantitative model of DNA content throughout embryogenesis in a copepod that possesses embryonic DNA elimination. We used densitometric image analysis to measure the DNA content of polar bodies, germline and somatic nuclei, and excised DNA "droplets." We report: 1) variable DNA contents of polar bodies, some of which do not contain the amount corresponding to the haploid germline genome size; 2) presence of pronuclei in newly laid embryo sacs; 3) gonomeric chromosomes in the second to fourth cleavage divisions and in the primordial germ cell and primordial endoderm cell during the fifth cleavage division; 4) timing of early embryonic cell stages, elimination of DNA, and divisions of the primordial germ cell and primordial endoderm cell at 22°C; and 5) persistence of a portion of the excised DNA "droplets" throughout embryogenesis. DNA elimination is a trait that spans multiple embryonic stages and a knowledge of the timing and variability of the associated cytological events with DNA elimination will promote the study of the molecular mechanisms involved in this trait. We propose the "genome yolk hypothesis" as a functional explanation for the persistence of the eliminated DNA that might serve as a resource during postdiminution cleavage divisions.

中文翻译:

Mesocyclops edax (S. A. Forbes, 1891) (Copepoda: Cyclopoida) 中的胚胎发育和程序性 DNA 消除的定量模型

在淡水浮游动物 Mesocyclops edax (SA Forbes, 1891) (甲壳纲:桡足类) 的胚胎中发生了染色体的高度程序化断裂和大量核 DNA 从前体细胞谱系中的消除(即染色质减少)。即使生殖系基因组保持完整,体细胞基因组也被重组并缩小到小五倍。我们在具有胚胎 DNA 消除的桡足类动物胚胎发生过程中提出了第一个全面的、定量的 DNA 含量模型。我们使用光密度图像分析来测量极体、种系和体细胞核以及切除的 DNA“液滴”的 DNA 含量。我们报告:1) 极体的可变 DNA 含量,其中一些不包含对应于单倍体种系基因组大小的数量;2) 在新放置的胚囊中存在原核;3) 第二至第四次卵裂分裂和第五次卵裂期原始生殖细胞和原始内胚层细胞中的染色体;4) 早期胚胎细胞阶段的时间、DNA 的消除以及原始生殖细胞和原始内胚层细胞在 22°C 下的分裂;和 5) 部分切除的 DNA“液滴”在整个胚胎发生过程中持续存在。DNA 消除是一种跨越多个胚胎阶段的性状,了解与 DNA 消除相关的细胞学事件的时间和可变性将促进对涉及该性状的分子机制的研究。我们提出“基因组蛋黄假说”
更新日期:2016-09-06
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