Eck Institute for Global Health, Department of Biological Sciences, University of Notre Dame, Notre Dame, IN 46556, USA.
Malar J. 2010 Oct 25;9:293. doi: 10.1186/1475-2875-9-293.
Alternative arrangements of chromosome 2 inversions in Anopheles gambiae are important sources of population structure, and are associated with adaptation to environmental heterogeneity. The forces responsible for their origin and maintenance are incompletely understood. Molecular characterization of inversion breakpoints provides insight into how they arose, and provides the basis for development of molecular karyotyping methods useful in future studies.
Sequence comparison of regions near the cytological breakpoints of 2Rb allowed the molecular delineation of breakpoint boundaries. Comparisons were made between the standard 2R+b arrangement in the An. gambiae PEST reference genome and the inverted 2Rb arrangements in the An. gambiae M and S genome assemblies. Sequence differences between alternative 2Rb arrangements were exploited in the design of a PCR diagnostic assay, which was evaluated against the known chromosomal banding pattern of laboratory colonies and field-collected samples from Mali and Cameroon.
The breakpoints of the 7.55 Mb 2Rb inversion are flanked by extensive runs of the same short (72 bp) tandemly organized sequence, which was likely responsible for chromosomal breakage and rearrangement. Application of the molecular diagnostic assay suggested that 2Rb has a single common origin in An. gambiae and its sibling species, Anopheles arabiensis, and also that the standard arrangement (2R+b) may have arisen twice through breakpoint reuse. The molecular diagnostic was reliable when applied to laboratory colonies, but its accuracy was lower in natural populations.
The complex repetitive sequence flanking the 2Rb breakpoint region may be prone to structural and sequence-level instability. The 2Rb molecular diagnostic has immediate application in studies based on laboratory colonies, but its usefulness in natural populations awaits development of complementary molecular tools.
染色体 2 倒位的替代排列是种群结构的重要来源，与对环境异质性的适应有关。导致它们产生和维持的力量还不完全清楚。反转断点的分子特征可深入了解它们的起源，并为开发未来研究中有用的分子核型分析方法提供基础。
通过比较细胞学断点附近的区域序列，实现了 2Rb 断点边界的分子划定。在标准的 2R+b 排列（PEST 参考基因组中的 An. gambiae）和 An. gambiae M 和 S 基因组组装中的倒置 2Rb 排列之间进行了比较。在设计 PCR 诊断检测时利用了替代 2Rb 排列之间的序列差异，该检测针对实验室培养物和来自马里和喀麦隆的野外采集样本的已知染色体带型进行了评估。
7.55 Mb 2Rb 倒位的断点由广泛的相同短（72 bp）串联组织序列组成，这可能是导致染色体断裂和重排的原因。分子诊断检测的应用表明，2Rb 在冈比亚按蚊及其姊妹种阿拉伯按蚊中只有一个共同的起源，标准排列（2R+b）可能通过断点重复使用两次而产生。该分子诊断在实验室培养物中应用可靠，但在自然种群中的准确性较低。
2Rb 断点区域侧翼的复杂重复序列可能容易发生结构和序列水平的不稳定性。2Rb 分子诊断在基于实验室培养物的研究中具有直接应用，但在自然种群中的有用性尚待开发互补的分子工具。
