Microsatellite accumulation on the Y chromosome inSilene latifolia

Abstract

The dioecious plant Silene latifolia possesses evolutionarily young sex chromosomes, and so serves as a model system to study the early stages of sex chromosome evolution. Sex chromosomes often differ distinctly from autosomes in both their structure and their patterns of evolution. The S. latifolia Y chromosome is particularly unique owing to its large size, which contrasts with the size of smaller, degenerate mammalian Y chromosomes. It is thought that the suppression of recombination on the S. latifolia Y chromosome could have resulted in the accumulation of repetitive sequences that account for its large size. Here we used fluorescence in situ hybridization (FISH) to study the chromosomal distribution of various microsatellites in S. latifolia including all possible mono-, di-, and tri-nucleotides. Our results demonstrate that a majority of microsatellites are accumulated on the q arm of the Y chromosome, which stopped recombining relatively recently and has had less time to accumulate repetitive DNA sequences compared with the p arm. Based on these results we can speculate that microsatellites have accumulated in regions that predate the genome expansion, supporting the view that the accumulation of repetitive DNA sequences occurred prior to, not because of, the degeneration of genes.

The Chromosomal Distribution of Microsatellite Repeats in the Genome of the Wolf Fish <i>Hoplias malabaricus</i>, Focusing on the Sex Chromosomes

“…Fluorescence in situ hybridization experiments were performed as described in Kubat et al [2008], with slight modifications. We used the following labeled oligonucleotides as probes: (GA) 15 , (CA) 15 , (C) 30 , (CAC) 10 , (GC) 15 , (CAA) 10 , (A) 30 , (CAG) 10 , (CAT) 10 , (GAG) 10 , (TAA) 10 and (CGG) 10 .…”

“…In H. malabaricus karyomorph B (XY system) microsatellites are accumulated in the heterochromatin of the X chromosome while e.g. in the dioecious plant Silene latifolia (evolutionary young XY system) microsatellites are more gathered on the Y chromosome [Kubat et al, 2008]. In H. malabaricus karyomorph D (X 1 X 2 neo-Y system) the localization of microsatellites on the neo-Y reflects its origin from 2 progenitor chromosomes.…”

Silene as a model system in ecology and evolution

“…S. latifolia Y genes show signs of degeneration, Silene as a model system in ecology and evolution G Bernasconi et al including fast protein evolution, mutations damaging sites known to be important for protein activity (Filatov, 2005c), low expression level and insertions of transposable elements in introns (Marais et al, 2008) and severely reduced polymorphism, an indirect effect of the processes that cause degeneration (Filatov et al, 2000). Cytogenetic analysis of S. latifolia chromosomes shows accumulation of repeat sequences on the Y chromosome (Kubat et al, 2007).…”

The role of repetitive DNA in structure and evolution of sex chromosomes in plants

“…Comparisons of microsatellite distributions between R. acetosa and S. latifolia chromosomes show that some motifs (for example, CAA or TAA) are strongly accumulated in non-recombining regions of the Y chromosome in both species (Figure 1), whereas other motifs have different patterns: (GC) 15 is abundant on the Y chromosomes in S. latifolia and absent in R. acetosa. Perhaps some simple DNA repeats regularly expand on Y chromosomes as speculated Kubat et al (2008). This may be because of their DNA conformational properties or dependent on other circumstances (for example, the stage of evolution of the sex chromosomes, co-transposition with some retroelements).…”