Abstract
The way in which transcriptional activity overcomes the physical DNA structure and gene regulation mechanisms involves complex processes that are not yet fully understood. Modifications in the cytosine-guanine sequence of DNA by 5-mC are preferentially located in heterochromatic regions and are related to gene silencing. Herein, we investigate evidence of epigenetic regulation related to the B chromosome model and transposable elements in A. scabripinnis. Indirect immunofluorescence using anti-5-mC to mark methylated regions was employed along with quantitative ELISA to determine the total genomic DNA methylation level. 5-mC signals were dispersed in the chromosomes of both females and males, with preferential accumulation in the B chromosome. In addition to the heterochromatic methylated regions, our results suggest that methylation is associated with transposable elements (LINE and Tc1-Mariner). Heterochromatin content was measured based on the C-band length in relation to the size of chromosome 1. The B chromosome in A. scabripinnis comprises heterochromatin located in the pericentromeric region of both arms of this isochromosome. In this context, individuals with B chromosomes should have an increased heterochromatin content when compared to individuals that do not. Although, both heterochromatin content and genome methylation showed no significant differences between sexes or in relation to the occurrence of B chromosomes. Our evidence suggests that the B chromosome can have a compensation effect on the heterochromatin content and that methylation possibly operates to silence TEs in A. scabripinnis. This represents a sui generis compensation and gene activity buffering mechanism.
Highlights
The way in which transcriptional activity overcomes the physical DNA structure and gene regulation mechanisms involves complex processes that are not yet fully understood.Epigenetic marking, characterized by a heritable and reversible change that regulates gene expression without modifying the DNA sequence [1], such as cytosine methylation, histone modifications, and interference RNA [2], is an open area of research for describing this process
The amount of transposable elements (TEs) in B− and B+ genomes shows a difference, since the B chromosome behaves as a deposit of moving elements
The B chromosomes of A. scabripinnis were composed of a greater amount of heterochromatin in the pericentromeric region of the short and long arms [18,19,20] and this study
Summary
The way in which transcriptional activity overcomes the physical DNA structure and gene regulation mechanisms involves complex processes that are not yet fully understood.Epigenetic marking, characterized by a heritable and reversible change that regulates gene expression without modifying the DNA sequence [1], such as cytosine methylation, histone modifications, and interference RNA [2], is an open area of research for describing this process. DNA methylation marks the silencing of gene regions [7] In this way, the inactivation of transposable elements (TEs) and repetitive elements can be the result of this epigenetic marking. Examples occur in ribosomal DNA sites (rDNA) of the fish Astyanax janeiroensis [8,9] or plants of the Citrus genus [5]. In this context, transposable elements that initiate their cycle with a small invasion in the genome, followed by an amplification of the number of copies, can lose their motility capacity through mutations (Kidwell and Lish, 2001) or by the action of epigenetic mechanisms [10,11]
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