Sequence Expression of Supernumerary B Chromosomes: Function or Fluff?

• Main Authors: Elena Dalla Benetta, Omar S. Akbari, Patrick M. Ferree
• Format: Article
• Language: English
• Published: MDPI AG 2019-02-01
• Series: Genes
• Subjects: B chromosomes; PSR (Paternal sex ratio); genome elimination; ncRNAs (non coding RNAs); selfish elements; super-Mendelian; repeated elements
• Online Access: https://www.mdpi.com/2073-4425/10/2/123

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.