Construction Of Genome Physical Map And Chromosome-wide Gene Expression Analysis In Swamp Eel(Monopterus Albus)

Swamp eel (Monopterus albus), an economical freshwater fish, possesses a characteristic of natural sex-reversal, from female-to-male transition through an intersex stage. The physiological characteristic makes swamp eel an ideal model for vertebrate sexual development. In addition, its 2n=24 karyotype stands for the minimum chromosome number in tolests as far as we know, implying that it may play an important role in the process of vertebrates evolution. Based on draft sequence of the swamp eel, I assembled the genome by fluorescence in situ hybridization to construct a genome-wide fine physical map. Further more, I identified the sex-related chromosome regions through gene expression profiling analysis during sex reversal. The main results are summarized as follows:1. Localizations of 186 Scaffolds on chromosonmes were determined by dual-color and three-color fluorescent in situ hybridization using the BACs and PCR fragments as the probes. Sequences in the total length of 550 Mb, approximately 80% of sequencing sequence, were assembled and anchored to chromosomes, which were grouped into twelve linkage groups corresponding to twelve chromosomes of swamp eel. Assembled size of each chromosome is proportional to the actual length of the chromosome. In accordance with the size of the chromosomes from large to small, the chromosomes of swamp eel were named as 1 to 12 chromosomes respectively, and the length of them were 75.9 Mb,65.1 Mb,51.6 Mb,51.2 Mb,50.1 Mb,48.1 Mb,42.4 Mb,42.0 Mb,41.9 Mb,35.0 Mb,29.3 Mb,22.8 Mb in turn. Combining sequence information, a total of 18,660 coding genes were located accurately. The number of genes on chromosome is proportional to the length of the chromosome.2. Chromosome-wide expressions during gonadal reversal were analyzed using RNA-seq data. A wide range of changes had taken place in gene expression. The overall number of expressed genes and expression level showed a trend of rising. The differentially expressed genes during sex reversal were grouped as up-regulated and down-regulated genes, which were mapped to chromosomes. The distribution of these genes were further analysised. No specific chromosome showed obvious expression differences associated with gonadal reversal. These differentially expressed genes were distributed on all chromosomes. However, the distribution of these genes was not totally scattered, they showed chromosome region bias. The functions of the genes with the region bias were further analysised by gene ontology in terms of biological process. The function of these genes were significantly enriched in signal transduction, organism differentiation and development and substance metabolism, suggesting that these genes are likely involved in the process of sex reversal in swamp eel.The construction of genome-wide fine physical map of swamp eel will be of great significance in studies of sex reversal mechanism, as well as in whole genome evolution of vertebrates. The chromosome distribution pattern of the genes related to sex reversal provide a new insight into sex development and sex chromosome evolution of vertebrates.