Dynamic Sequence Evolution of a Sex-Associated B Chromosome in Lake Malawi Cichlid Fish
Dynamic Sequence Evolution of a Sex-Associated B Chromosome in Lake Malawi Cichlid Fish
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DOI：
10.1093/jhered/esw059
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发表时间：
2017-01-01
影响因子：
3.1
通讯作者：
Kocher, Thomas D.
中科院分区：
文献类型：
--
作者：
Clark, Frances E.;Conte, Matthew A.;Kocher, Thomas D.
B 染色体是在许多植物、动物和真菌物种中发现的额外染色体。 B 染色体经常操纵常见的细胞过程以增加其频率，有时会损害有机体的健康。在这里，我们表征了几种马拉维湖慈鲷鱼的 B 染色体。 Metriaclima 斑马“Boadzulu”个体的全基因组测序揭示了具有异常高序列覆盖率的序列块，表明这些序列的拷贝数增加。这些高序列覆盖度的区域仅在雌性中发现。高拷贝数序列特有的 SNP 允许设计特异性扩增引物。这些引物仅在携带细胞学鉴定的 B 染色体（B 载体）的 Metriaclima lombardoi 个体中扩增片段，表明这些额外的拷贝位于 B 染色体上。这些相同的引物被用来鉴定马拉维湖其他物种中携带 B 的个体。在 7 个物种的 323 名雌性中，总共鉴定出 43 名 B 携带者。 B 携带者全部为女性；在接受调查的这些物种的 317 名雄性中没有观察到 B 染色体。对 B 特异性序列块的拷贝数变异的定量分析表明，B 携带者拥有单个 B 染色体，与之前隆巴多分枝杆菌的核型分析一致。 B 携带者中的单个 B 染色体与 2 种潜在的驱动机制一致：一种涉及种系之前有丝分裂中的不分离和优先分离，另一种涉及减数分裂 I 期间的优先分离。
B chromosomes are extra chromosomes found in many species of plants, animals, and fungi. B chromosomes often manipulate common cellular processes to increase their frequency, sometimes to the detriment of organismal fitness. Here, we characterize B chromosomes in several species of Lake Malawi cichlid fish. Whole genome sequencing of Metriaclima zebra "Boadzulu" individuals revealed blocks of sequence with unusually high sequence coverage, indicative of increased copy number of those sequences. These regions of high sequence coverage were found only in females. SNPs unique to the high copy number sequences permitted the design of specific amplification primers. These primers amplified fragments only in Metriaclima lombardoi individuals that carried a cytologically identified B chromosome (B-carriers), indicating these extra copies are located on the B chromosome. These same primers were used to identify B-carrying individuals in additional species from Lake Malawi. Across 7 species, a total of 43 B-carriers were identified among 323 females. B-carriers were exclusively female; no B chromosomes were observed in the 317 males surveyed from these species. Quantitative analysis of the copy number variation of B-specific sequence blocks suggests that B-carriers possess a single B chromosome, consistent with previous karyotyping of M. lombardoi. A single B chromosome in B-carriers is consistent with 2 potential drive mechanisms: one involving nondisjunction and preferential segregation in a mitotic division prior to the germ-line, and the other involving preferential segregation during meiosis I.