Site-specific recombinases are widely used tools for analysis of genetics, development and cell biology, and many schemes have been devised to alter gene expression by recombinase-mediated DNA rearrangements. Because the FRT and lox target sites for the commonly used FLP and Cre recombinases are asymmetrical, and must pair in the same direction to recombine, construct design must take into account orientation of the target sites. Both direct and inverted configurations have been used. However, the consequence of recombination between target sites on sister chromatids is frequently overlooked. This is especially consequential with inverted target sites, where exchange between oppositely oriented target sites on sisters will produce dicentric and acentric chromosomes. By using constructs that have inverted target sites in Drosophila melanogaster and in mice, we show here that dicentric chromosomes are produced in the presence of recombinase, and that the frequency of this event is quite high. The negative effects on cell viability and behavior can be significant, and should be considered when using such constructs.

中文翻译：

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反向靶位点之间的位点特异性重组产生双着丝粒/无着丝粒染色体。

位点特异性重组酶是广泛用于遗传学，发育和细胞生物学分析的工具，并且已设计出许多方案来通过重组酶介导的DNA重排改变基因表达。因为常用的FLP和Cre重组酶的FRT和lox目标位点是不对称的，并且必须在同一方向上配对才能重组，所以构建体设计必须考虑目标位点的方向。直接配置和倒置配置均已使用。然而，经常忽略姐妹染色单体上靶位点之间重组的结果。这对于倒转的靶位点尤其重要，在姐妹位相反方向的靶位点之间的交换将产生双着丝粒和无着丝粒染色体。通过使用在果蝇和小鼠中具有反向靶位点的构建体，我们在此处显示了在重组酶存在下产生了双着丝粒染色体，并且该事件的发生频率很高。对细胞活力和行为的负面影响可能很明显，在使用此类构建体时应予以考虑。