Sequencing of Supernumerary Chromosomes of Red Fox and Raccoon Dog Confirms a Non-Random Gene Acquisition by B Chromosomes

Abstract

B chromosomes (Bs) represent a variable addition to the main karyotype in some lineages of animals and plants. Bs accumulate through non-Mendelian inheritance and become widespread in populations. Despite the presence of multiple genes, most Bs lack specific phenotypic effects, although their influence on host genome epigenetic status and gene expression are recorded. Previously, using sequencing of isolated Bs of ruminants and rodents, we demonstrated that Bs originate as segmental duplications of specific genomic regions, and subsequently experience pseudogenization and repeat accumulation. Here, we used a similar approach to characterize Bs of the red fox (Vulpes vulpes L.) and the Chinese raccoon dog (Nyctereutes procyonoides procyonoides Gray). We confirm the previous findings of the KIT gene on Bs of both species, but demostrate an independent origin of Bs in these species, with two reused regions. Comparison of gene ensembles in Bs of canids, ruminants, and rodents once again indicates enrichment with cell-cycle genes, development-related genes, and genes functioning in the neuron synapse. The presence of B-chromosomal copies of genes involved in cell-cycle regulation and tissue differentiation may indicate importance of these genes for B chromosome establishment.

B Chromosomes in Grasshoppers: Different Origins and Pathways to the Modern Bs

“…Small unique DNA fragments of the main genome could probably also be inserted into the B s without forming C-negative region. This phenomenon was described in studies of some B s in mammals [ 19 , 20 , 21 ].…”

“…For example, the C-positive Ba1 in E. plorans contained small regions painted with euchromatic DNA probe ( Figure 10 a,d). The sequencing of microdissected libraries of mammalian B s revealed DNA fragments homologous to a unique DNA located in different chromosomes of the basic set [ 19 , 20 , 21 ]. The question “are the C-negative regions of the B s the remnants of large euchromatic regions earlier present in the B or are they the result of multiple insertions/duplications of a small euchromatic chromosome region?” remains open.…”

“…The ITS from the autosome S11 appeared to be the closest one to the ITS from the B chromosome [ 18 ]. We should also note that sequencing of B s in six mammalian species showed that B s can contain DNA fragments from different A s [ 19 , 20 , 21 ], which significantly puzzles the question of the B s origin.…”

Genome and Karyotype Reorganization after Whole Genome Duplication in Free-Living Flatworms of the Genus Macrostomum

“…However, we should note that the revealed B chromosomes open a new possibility for analysis of amplified DNA repeats in M. mirumnovem. Microdissected DNA libraries can be generated from B chromosomes and then used for NGS sequencing, as was done previously for the Bs in some species of different taxa [45][46][47]. The study of B chromosomes in M. mirumnovem, including the generation of microdissected libraries and their sequencing is in progress.…”

The occurrence of dot-like micro B chromosomes in Korean field mice Apodemus peninsulae from the shore of the Teletskoye Lake (Altai Mountains)

“…Rubtsov and Borisov (2018) suggest several models of B chromosome origin, while the article by Vujošević et al (2018), provides an updated list of 85 mammalian species with Bs, and gives a detail description of research experiments accomplished on these species. The research article by (Makunin et al 2018) provides novel data on B chromosome content and evolution in the red fox (the first mammalian species with Bs, whose genome has recently been sequenced and assembled , and in the raccoon dog, the carnivore species, where B specific coding genes were discovered almost 13 years ago. Using new generation sequencing, the authors argue that the origin of B chromosome in these species is independent.…”