Abstract
Young sex chromosomes possess unique and ongoing dynamics that allow us to understand processes that have an impact on their evolution and divergence. The genus Silene includes species with evolutionarily young sex chromosomes, and two species of section Melandrium, namely Silene latifolia (24, XY) and Silene dioica (24, XY), are well-established models of sex chromosome evolution, Y chromosome degeneration, and sex determination. In both species, the X and Y chromosomes are strongly heteromorphic and differ in the genomic composition compared to the autosomes. It is generally accepted that for proper cell division, the longest chromosomal arm must not exceed half of the average length of the spindle axis at telophase. Yet, it is not clear what are the dynamics between males and females during mitosis and how the cell compensates for the presence of the large Y chromosome in one sex. Using hydroxyurea cell synchronization and 2D/3D microscopy, we determined the position of the sex chromosomes during the mitotic cell cycle and determined the upper limit for the expansion of sex chromosome non-recombining region. Using 3D specimen preparations, we found that the velocity of the large chromosomes is compensated by the distant positioning from the central interpolar axis, confirming previous mathematical modulations.
Highlights
Accepted theory predicts that the sex chromosomes originate from a single pair of autosomes [1]
The repetitive fraction in the non-recombining region affects local gene expression and may increase the overall methylation of neighbouring sequences, stimulating the process of Y chromosome inactivation. Such sex chromosome upsizing was well was described for the large Y chromosome in Coccinia grandis [14] or Silene species of section Melandrium [13,15]
The models with evolutionary young sex chromosomes are important to study the early steps of sex chromosome evolution and answer fundamental questions of sex chromosome biology [5,16]
Summary
Accepted theory predicts that the sex chromosomes originate from a single pair of autosomes [1]. Plant sex chromosomes evolved relatively recently and independently across a wide diversity of taxa, displaying a huge variety of X(Z) and Y(W) chromosome divergence [2] Despite their independent origin, they share similar evolutionary characteristics, including recombination suppression, Y (W) chromosome degeneration, and dosage compensation, representing exceptional features of genomic convergence [3]. The repetitive fraction in the non-recombining region affects local gene expression and may increase the overall methylation of neighbouring sequences, stimulating the process of Y chromosome inactivation. Such sex chromosome upsizing was well was described for the large Y chromosome in Coccinia grandis [14] or Silene species of section Melandrium [13,15]. The models with evolutionary young sex chromosomes are important to study the early steps of sex chromosome evolution and answer fundamental questions of sex chromosome biology [5,16]
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