The regulation and evolution of amphioxus sex determination

The sex of animals is often decided by one of the chromosomes. In human, men have a Y and an X chromosome, and women have two X chromosomes. In birds, thats opposite: females have two different chromosomes called Z and W chromosomes and males have two Z chromosomes. The XY or ZW chromosomes are called sex chromosomes. In many other species, however, its unclear if they have sex chromosomes. This project studies the sex-determining system in amphioxus. Amphioxus is an invertebrate group, but is closely related to vertebrate. Because amphioxus share many physiological features with vertebrate and evolve slowly, researchers believe amphioxus represents a useful model to study vertebrate evolution. We have decoded the genomes of three amphioxuses: Florida amphioxus, Japanese amphioxus and Chinese amphioxus, and we are looking for the sex chromosomes in their genomes. To do this, we will compare the male and female genomes of many individuals and find out the difference. Because the sex chromosomes differ between males and females, the chromosome that bears the sex-linked difference should be the sex chromosome. Once we have found the sex chromosomes, we will ask how the sex chromosomes contribute to the physiological differences between males and females, particularly the gonads. We will look closely at the genes located at the sex chromosomes, and find out which genes are expressed (produce proteins) differentially in the gonads. Those genes function to decide whether the undifferentiated gonads will develop into testis and ovary that determine the sex of the animals. Those genes are called sex-determining genes. We will then ask how the sex-determining genes are differentially expressed in the gonads. To do so, we will examine sequence elements that are responsible for gene regulation. Those elements include promoters and enhancers. We will use cutting-edge sequencing technologies (ATAC-seq and ChIP-seq) to compare the activities of those elements during gonad development between males and females. Finally, to verify the functions of the sex-determining gene and the regulatory elements, we will delete them from the genome using the gene-editing technique. The deletion of the sex- determining gene or the regulatory elements is expected to cause sex-reversal to the animals.

The sex of animals is often decided by one of the chromosomes. In human, men have a Y and an X chromosome, and women have two X chromosomes. In birds, that's opposite: females have two different chromosomes called Z and W chromosomes and males have two Z chromosomes. The XY or ZW chromosomes are called sex chromosomes. In many other species, however, it's unclear if they have sex chromosomes. This project studies the sex-determining system in amphioxus. Amphioxus is an invertebrate group, but is closely related to vertebrate. Because amphioxus share many physiological features with vertebrate and evolve slowly, researchers believe amphioxus represents a useful model to study vertebrate evolution. We have decoded the genomes of three amphioxuses: Florida amphioxus, Japanese amphioxus and Chinese amphioxus, and we are looking for the sex chromosomes in their genomes. To do this, we will compare the male and female genomes of many individuals and find out the difference. Because the sex chromosomes differ between males and females, the chromosome that bears the sex-linked difference should be the sex chromosome. Once we have found the sex chromosomes, we will ask how the sex chromosomes contribute to the physiological differences between males and females, particularly the gonads. We will look closely at the genes located at the sex chromosomes, and find out which genes are expressed (produce proteins) differentially in the gonads. Those genes function to decide whether the undifferentiated gonads will develop into testis and ovary that determine the sex of the animals. Those genes are called sex-determining genes. We will then ask how the sex-determining genes are differentially expressed in the gonads. To do so, we will examine sequence elements that are responsible for gene regulation. Those elements include promoters and enhancers. We will use cutting-edge sequencing technologies (ATAC-seq and ChIP-seq) to compare the activities of those elements during gonad development between males and females. Finally, to verify the functions of the sex-determining gene and the regulatory elements, we will delete them from the genome using the gene-editing technique. The deletion of the sex-determining gene or the regulatory elements is expected to cause sex-reversal to the animals.