LeRiche Kaitlynn, Eagle Shannon H C, Crease Teresa J
Department of Integrative Biology, University of Guelph, Guelph, Ontario, N1G 2W1, Canada.
PLoS One. 2014 Dec 9;9(12):e114773. doi: 10.1371/journal.pone.0114773. eCollection 2014.
Pokey is a class II DNA transposon that inserts into 28S ribosomal RNA (rRNA) genes and other genomic regions of species in the subgenus, Daphnia. Two divergent lineages, PokeyA and PokeyB have been identified. Recombination between misaligned rRNA genes changes their number and the number of Pokey elements. We used quantitative PCR (qPCR) to estimate rRNA gene and Pokey number in isolates from natural populations of Daphnia obtusa, and in clonally-propagated mutation accumulation lines (MAL) initiated from a single D. obtusa female. The change in direction and magnitude of Pokey and rRNA gene number did not show a consistent pattern across ∼ 87 generations in the MAL; however, Pokey and rRNA gene number changed in concert. PokeyA and 28S gene number were positively correlated in the isolates from both natural populations and the MAL. PokeyB number was much lower than PokeyA in both MAL and natural population isolates, and showed no correlation with 28S gene number. Preliminary analysis did not detect PokeyB outside rDNA in any isolates and detected only 0 to 4 copies of PokeyA outside rDNA indicating that Pokey may be primarily an rDNA element in D. obtusa. The recombination rate in this species is high and the average size of the rDNA locus is about twice as large as that in other Daphnia species such as D. pulicaria and D. pulex, which may have facilitated expansion of PokeyA to much higher numbers in D. obtusa rDNA than these other species.
Pokey是一种II类DNA转座子，可插入水蚤亚属物种的28S核糖体RNA（rRNA）基因和其他基因组区域。已鉴定出两个不同的谱系，即PokeyA和PokeyB。未对齐的rRNA基因之间的重组会改变它们的数量以及Pokey元件的数量。我们使用定量PCR（qPCR）来估计钝额水蚤自然种群分离株以及由单个钝额水蚤雌性启动的克隆繁殖突变积累系（MAL）中的rRNA基因和Pokey数量。在MAL中约87代的过程中，Pokey和rRNA基因数量的变化方向和幅度没有显示出一致的模式；然而，Pokey和rRNA基因数量是协同变化的。在自然种群和MAL的分离株中，PokeyA和28S基因数量呈正相关。在MAL和自然种群分离株中，PokeyB的数量远低于PokeyA，并且与28S基因数量没有相关性。初步分析在任何分离株的rDNA之外均未检测到PokeyB，并且在rDNA之外仅检测到0至4个PokeyA拷贝，这表明Pokey在钝额水蚤中可能主要是一种rDNA元件。该物种的重组率很高，rDNA位点的平均大小约为其他水蚤物种（如蚤状溞和大型溞）的两倍，这可能促进了PokeyA在钝额水蚤rDNA中的数量比其他物种扩展得更高。
