Award details

The evolution of chromosome structure meiotic pairing and silencing of the heterologous sex chromosomes in the plant genus Silene

Reference	BB/E002765/2
Principal Investigator / Supervisor	Professor Dmitry Filatov
Co-Investigators / Co-Supervisors	Dr Susan Armstrong
Institution	University of Oxford
Department	Plant Sciences
Funding type	Research
Value (£)	230,214
Status	Completed
Type	Research Grant
Start date	01/09/2007
End date	31/12/2009
Duration	28 months

Abstract

Previous studies of sex chromosome evolution in the plant genus Silene have been mainly focused on population genetics processes, and little is known about the structural and functional changes at the cytogenetic level. We plan to use our recently developed tools for Arabidopsis meiosis to analyse the structure and behaviour of the X and Y chromosomes in Silene meiosis. We will use high resolution fluorescent in situ hybridisation (FISH) to conduct a comparative cytogenetic analysis of sex chromosomes in dioecious Silene, and in non-dioecious Silene species without sex chromosomes, which is most likely the ancestral state in Silene. Already isolated sex-linked genes as well as fosmid clones from the available S. latifolia genomic library will be used as FISH probes. Our FISH protocol has proved to work well on Silene chromosomes. We will also conduct a detailed molecular cytogenetic analysis of recently evolved Silene latifolia sex chromosomes to test whether their behaviour in meiosis is similar to that observed in mammalian sex chromosomes. A panel of available antibodies generated against structural and recombination proteins in Arabidopsis will be used to follow the progression of meiosis and sex chromosome pairing in S. latifolia. The formation of synaptonemal complex, an ultrastructural feature of paired homologous chromosomes will be studied using transmission electron microscopy as this will give us the opportunity to analyse the extent of the pairing regions. The non-recombining regions of S. latifolia sex chromosomes will be analysed to determine whether they are silenced during male meiosis, as happens in sex vesicle in mammals. Analyses will be conducted in a number of other Silene species with and without sex chromosomes. This will provide an evolutionary perspective on changes in the structure and function of sex chromosomes in the genus Silene and will help us to understand the general processes involved in sex chromosome evolution.

Summary

Human individuals normally develop as either a male or a female and the genetic mechanism that determines the sex of an organism is based on sex chromosomes: Females have two X chromosomes, while males have one X and one Y chromosome, which is male-specific. During embryonic development the individual genes on the Y chromosome trigger a chain of events leading to the development of a male. Apart from the sex chromosomes, cells contain other chromosomes, called autosomes. Each chromosome is normally represented twice, for example, in the human there are 46 chromosomes, consisting of a pair of sex chromosomes and 22 pairs of autosomes. In the egg and sperm the chromosomes are represented once. In order to achieve this the meiotic pathway occurs, the chromosomes form pairs, which is relatively straightforward for the autosomes and XX in females. Things become more complicated when two different sex chromosomes, X and Y, have to pair in males. The cell has to ensure that a correct pairing is formed between the X and Y chromosomes and depends on pairing in a small region that is similar in both chromosomes, known as the pairing region. The mechanisms involved in these processes are studied to some extent in humans and the mouse, but no information is available for independently evolved plant sex chromosomes. Understanding how sex chromosomes have evolved independently in evolution and how they function in different organisms is of great biological interest. In this project we will study how plant sex chromosomes make sure the pairing occurs correctly and how the structure and function of plant sex chromosomes evolved. Plants often have male and female organs on the same individual. Species with separate male and female individuals are rare in plants and some of these species are known to contain sex chromosomes. The white campion, Silene latifolia has separate sexes (male and female plants) and has a sex chromosome system similar to mammals; females have two X chromosomes, while males contain X and Y chromosomes. The sex determination system in this species is relatively young and likely to have evolved 10-15 million years ago (MYA) compared to ~320 MYA in mammals. Sex chromosomes have evolved only in a few species of the genus Silene, allowing us to compare the structure and behaviour of chromosomes in species with and without sex chromosomes. This provides a unique opportunity to study evolutionary changes that have led to sex chromosome evolution. The two questions we want to understand are how have the sex chromosomes evolved in the campions, and how they negotiate meiosis successfully, given the X and Y chromosomes are largely different to each other and therefore have specific problems in pairing, synapsis and recombination. For this purpose we will search for DNA probes that hybridise specifically with S. latifolia sex chromosomes. The location of these probes on the sex chromosomes (and chromosomes homologous to sex chromosomes) in different species will be studied and compared using fluorescent in situ hybridisation, the method which allows to localise fluorescent-labelled DNA probes hybridised to chromosomes fixed to a glass slide. The pairing of sex chromosomes during cell devision (meiosis) will be studied using fluorescent-labelled antibodies, the proteins that specifically bind other proteins, in our case the proteins involved in chromosome pairing and recombination. Using these tools we will be able to observe the paired and unpaired regions of the sex chromosomes as fluorescing foci on chromosome spreads. The comparison of structure and meiotic behaviour of sex chromosomes in Silene on the one hand and mammals on the other will help to understand whether and to what extent meiotic processes and controls are conserved across all eukaryotes. A plant model such as the one provided by the Silene genus is very advantageous and likely to be useful for general principles in meiosis and therefore reproduction in humans.

Committee	Closed Committee - Genes & Developmental Biology (GDB)
Research Topics	Plant Science
Research Priority	X – Research Priority information not available
Research Initiative	X - not in an Initiative
Funding Scheme	X – not Funded via a specific Funding Scheme

Associated awards:

BB/E002765/1 The evolution of chromosome structure meiotic pairing and silencing of the heterologous sex chromosomes in the plant genus Silene

I accept the terms and conditions of use (opens in new window)

export PDF file

back to list new search