W. M. Keck Science Department of Claremont McKenna, Pitzer, and Scripps Colleges, Claremont, CA 91711, USA.
Division of Biological Sciences, Section of Cell and Developmental Biology, University of California, San Diego, La Jolla, CA 92093, USA.
Genes (Basel). 2019 Feb 8;10(2):123. doi: 10.3390/genes10020123.
B chromosomes are enigmatic heritable elements found in the genomes of numerous plant and animal species. Contrary to their broad distribution, most B chromosomes are non-essential. For this reason, they are regarded as genome parasites. In order to be stably transmitted through generations, many B chromosomes exhibit the ability to "drive", i.e., they transmit themselves at super-Mendelian frequencies to progeny through directed interactions with the cell division apparatus. To date, very little is understood mechanistically about how B chromosomes drive, although a likely scenario is that expression of B chromosome sequences plays a role. Here, we highlight a handful of previously identified B chromosome sequences, many of which are repetitive and non-coding in nature, that have been shown to be expressed at the transcriptional level. We speculate on how each type of expressed sequence could participate in B chromosome drive based on known functions of RNA in general chromatin- and chromosome-related processes. We also raise some challenges to functionally testing these possible roles, a goal that will be required to more fully understand whether and how B chromosomes interact with components of the cell for drive and transmission
B 染色体是存在于许多植物和动物物种基因组中的神秘可遗传元素。与它们广泛的分布相反，大多数 B 染色体是非必需的。因此，它们被视为基因组寄生虫。为了能够稳定地通过世代传递，许多 B 染色体表现出“驱动”的能力，即它们通过与细胞分裂装置的定向相互作用，以超孟德尔频率将自身传递给后代。迄今为止，对于 B 染色体如何驱动的机制，人们知之甚少，尽管一种可能的情况是 B 染色体序列的表达起作用。在这里，我们重点介绍了一些以前鉴定的 B 染色体序列，其中许多是重复的和非编码的，它们在转录水平上被证明是表达的。我们推测每一种表达序列如何根据 RNA 在一般染色质和染色体相关过程中的已知功能参与 B 染色体驱动。我们还提出了一些功能测试这些可能角色的挑战，这是一个目标，将需要更充分地了解 B 染色体是否以及如何与细胞的成分相互作用，以进行驱动和传递。
