First report on B chromosome content in a reptilian species: the case of Anolis carolinensis

Abstract

Supernumerary elements of the genome are often called B chromosomes. They usually consist of various autosomal sequences and, because of low selective pressure, are mostly pseudogenized and contain many repeats. There are numerous reports on B chromosomes in mammals, fish, invertebrates, plants, and fungi, but only a few of them have been studied using sequencing techniques. However, reptilian supernumerary chromosomes have been detected only cytogenetically and never sequenced or analyzed at the molecular level. One model squamate species with available genome sequence is Anolis carolinensis. The scope of the present article is to describe the genetic content of A. carolinensis supernumerary chromosomes. In this article, we confirm the presence of B chromosomes in this species by reverse painting and synaptonemal complex analysis. We applied low-pass high-throughput sequencing to analyze flow-sorted B chromosomes. Anole B chromosomes exhibit similar traits to other supernumerary chromosomes from different taxons: they contain two genes related to cell division control (INCENP and SPIRE2), are enriched in specific repeats, and show a high degree of pseudogenization. Therefore, the present study confirms that reptilian B chromosomes resemble supernumerary chromosomes of other taxons.

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

“…At least a half of these genes are transcriptionally active [ 71 ]. It should be noted that these genes are involved in cell division processes as well as the genes of B s of vertebrates [ 19 , 20 , 21 , 72 , 73 , 74 ]. However, the exact location and flanking regions of these genes are mostly unknown.…”

The Modern View of B Chromosomes Under the Impact of High Scale Omics Analyses

“…In addition to repetitive DNA, pseudogene-like sequences have also been reported to be located on Bs [56,74,75]. We assume that these pseudogenes might have formed as a result of intensive rearrangements and frequent sequence duplications in A chromosomes.…”

“…Apart from the presence of transposons and pseudogenes/fragments of genes on Bs, the latest research studies [25,44,56,75,77,78,79] have also found protein coding intact genes that we call “B essential genes” (see definitions in Box 1) which might be critical for the survival and transmission of Bs during their earlier stages of evolution (see details in next topic section). To create a reference of B-linked genes, we have organized a database that contain a list of genes detected in different species (Supplementary Dataset S1).…”

“…According to this study, the most significant terms in biological processes detected from Gene Ontology (GO) analysis in the B chromosome of maize are cellular processes and metabolic processes, while that of molecular functions showed most of the genes being involved in ribonucleotide and deoxyribonucleotide binding. The sequencing analysis of flow sorted Bs in the reptilian species Anolis carolinensis detected cell division associated genes, namely INCENP and SPIRE2 [75]. The characterization of B sequences in Chinese racoon dog and red fox have discovered B-located genes encoding functions for development, cell cycle and neuron synapses [55].…”

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.…”