Genome Sequence Of Swamp Eel Provides Insights Into Genome Evolution And Sex Reversal

Genome evolution is essential to speciation and diversity of vertebrates. Teleost fish is the ancestor of vertebrates and possess an important position in the vertebrate evolution. Another pivotal event in the vertebrate genome evolution is the emergence of sex chromosomes. Mammalian sex is determined by female XX/male XY system while bird sex is controlled by a ZW female and ZZ male system, which split 310 million years ago (Mya) and shows no homology with each other. However, the understanding of sex chromosome origin in the teleosts remains unknown. The teleost swamp eel(Monopterus albus) can reverse its sex naturally. In this study, I sequenced and assembled the whole genome and transcriptome of swamp eel, analyzed the genome evolution of vertebrates, aiming to investigate genome evolution, origin of sex chromosomes and sexual reversal mechanisms. The main results are summarized as follows:1. The genome of swamp eel was compact as revealed by the analysis of genome characteristics. Most of the duplicated sequences were lost after whole genome duplication (WGD), which resulted in low content of genomic repeative sequences and segmental duplications (SDs), while the number of the coding genes was stable.2. The teleost ancestor had 24 primitive chromosomes as the teleost-specific WGD (3R) from the 12 proto-chromosomes of the vertebrate ancestor. Then the chromosomes of the swamp eel were further fused to result in the current karyotype of 12 chromosomes.3. The co-existence of primitive mammal-like X and bird-like Z chromosomes in the vertebrate ancestor genome, indicating a common sex chromosome repertoire from which modern X chromosome in mammals and Z chromosome in birds and their conserved roles in sex determination.4. The sex chromosome related genes are closely associated with gonad reversal through a group of sex genes led by Sox3/Dmrtl and pluripotent stem cell factors Nanog?Klf?Oct4?c-Myc and Tert corporately.