Regulation of meiotic recombination across sex chromosomes

A key step in the evolution of heteromorphic sex chromosomes is the suppression of meiotic recombination between the evolving homologs. In the heterogametic sex (i.e. X/Y or Z/W), recombination rates in some regions are orders of magnitude above genome-wide averages, whereas other regions experience complete suppression of crossing over between the chromosomes. We are interested in understanding the mechanisms regulating homologous recombination across newly evolving sex chromosomes. We are exploring multiple stages in this process, including how double strand breaks are initiated across sex chromosomes and how double strand breaks are repaired.

 
Threespine stickleback testis cells undergoing meiosis. Cells stained brown are expressing the evolutionarily conserved protein, DMC1, a key component for the repair of DNA double strand breaks.

Threespine stickleback testis cells undergoing meiosis. Cells stained brown are expressing the evolutionarily conserved protein, DMC1, a key component for the repair of DNA double strand breaks.

Threespine stickleback male chromosomes paired during pachytene stage of meiosis.

Threespine stickleback male chromosomes paired during pachytene stage of meiosis.

 
 

Genetic mechanisms of sex determination

Threespine stickleback fish have a recently derived XY sex determination system, where sex is genetically determined. The key Y chromosome-linked sex determination gene remains to be identified. We are interested in understanding what genes on the Y chromosome are involved in sex determination as well as the underlying genes across the genome involved in the differentiation of sex. There is a tremendous diversity of sex determination mechanisms among animals and the closely related species of stickleback fish are not an exception to this pattern. Multiple species of stickleback fish have independently derived sex chromosomes. We are interested in exploring sex determination in different stickleback species to more broadly understand the plasticity of sex determination observed across animals.

Male threespine stickleback fish exhibit unique coloration patterns from females. These fish were collected from Port Gardner Bay in Everett, Washington.

Male threespine stickleback fish exhibit unique coloration patterns from females. These fish were collected from Port Gardner Bay in Everett, Washington.

Sex determination occurs during early embryonic development in threespine stickleback fish.

Sex determination occurs during early embryonic development in threespine stickleback fish.

Male threespine stickleback fish exhibit unique coloration patterns from females. These fish were collected from Port Gardner Bay in Everett, Washington.

Male threespine stickleback fish exhibit unique coloration patterns from females. These fish were collected from Port Gardner Bay in Everett, Washington.

 

Genetic diversity of Y chromosomes

An increasing number of Y chromosome assemblies have revealed an incredible degree of diversity in sequence and structure among species. Within species we understand comparatively little about Y chromosome diversity. One clear advantage of using threespine stickleback fish as a model system is the large number of genetically isolated freshwater and marine populations distributed throughout the northern hemisphere. We are leveraging multiple populations to explore the parallel evolution of Y chromosomes. Combined with a reference Y chromosome assembly, we are using several long-read sequencing technologies to understand how sequence and structure varies among Y chromosomes within species.