Biémont C, Vieira C, Hoogland C, Cizeron G, Loevenbruck C, Arnault C, Carante J P
Université Lyon 1, Villeurbanne, France.
Genetica. 1997;100(1-3):161-6.
To investigate the main forces controlling the containment of transposable elements (TE) in natural populations, we analyzed the copia, mdg1, and 412 elements in various populations of Drosophila melanogaster and D. simulans. A lower proportion of insertion sites on the X chromosome in comparison with the autosomes suggests that selection against the detrimental effects of TE insertions is the major force containing TE copies in populations of Drosophila. This selection effect hypothesis is strengthened by the absence of the negative correlation between recombinaiton rate and TE copy number along the chromosomes, which was expected under the alternative ectopic exchange model (selection against the deleterious rearrangements promoted by recombination between TE insertions). A cline in 412 copy number in relation to latitude was observed among the natural populations of D. simulans, with very high numbers existing in some local populations (around 60 copies in a sample from Canberra, Australia). An apparent absence of selection effects in this Canberra sample and a value of transposition rate equal to 1-2 x 10(-3) whatever the population and its copy number agree with the idea of recent but temporarily drastic TE movements in local populations. The high values of transposition rate in D. simulans clearly disfavor the hypothesis that the low amount of transposable elements in this species could result from a low transposition rate.
为了研究控制自然种群中转座元件（TE）抑制的主要力量，我们分析了黑腹果蝇和拟暗果蝇不同种群中的copia、mdg1和412元件。与常染色体相比，X染色体上插入位点的比例较低，这表明针对TE插入有害效应的选择是果蝇种群中抑制TE拷贝数的主要力量。沿着染色体，重组率与TE拷贝数之间不存在负相关，而在替代的异位交换模型（针对TE插入之间重组促进的有害重排的选择）下这是预期的，这强化了这种选择效应假说。在拟暗果蝇的自然种群中观察到412拷贝数与纬度相关的渐变群，在一些当地种群中存在非常高的拷贝数（来自澳大利亚堪培拉的一个样本中约有60个拷贝）。在这个堪培拉样本中明显不存在选择效应，并且无论种群及其拷贝数如何，转座率的值都等于1 - 2×10⁻³，这与当地种群近期但暂时剧烈的TE移动的观点一致。拟暗果蝇中转座率的高值明显不支持该物种中转座元件数量少可能是由于转座率低这一假说。
