Aquaculture has been believed to be a major Chinese contribution to the world. In recent 20 years, genome and other genetic technologies have promoted significant advances in basic studies on molecular basis and genetic improvement of aquaculture animals, and complete genomes of some main aquaculture animals have been sequenced or announced to be sequenced since the beginning of this century. Here, we review some significant breakthrough progress of aquaculture genetic improvement technologies including genome technologies, somatic cell nuclear transfer and stem cell technologies, outline the molecular basis of several economically important traits including reproduction, sex, growth, disease resistance, cold tolerance and hypoxia tolerance, and present a series of candidate trait-related genes. Finally, some application cases of genetic improvement are introduced in aquaculture animals, especially in China, and several development trends are highlighted in the near future.

The pluripotency of mouse embryonic stem (ES) cells is maintained by self-renewal. To screen for genes essential for this process, we constructed an RNA interference (RNAi) library by inserting subtracted ES cell cDNA fragments into plasmid containing two opposing cytomegalovirus promoters. ES cells were transfected with individual RNAi plasmids and levels of the pluripotency marker Oct-4 were monitored 48 hours later by real time RT-PCR. Of the first 89 RNAi plasmids characterized, 12 downregulated Oct-4 expression to less than 50% of the normal level and 7 of them upregulated Oct-4 expression to more than 150% of the normal level. To investigate their long-term effect on self-renewal, ES cells were transfected by these 19 RNAi plasmids individually and G418-resistant colonies were subjected to alkaline phosphatase (AP) staining after 7 days selection. Except for 4 plasmids that caused cell death, the ratio of AP positive colonies was repressed to less than 60% of the control group by the other 15 plasmids and even below 20% by 10 plasmids. The cDNA fragments in these 10 plasmids correspond to eight genes, including Zfp42/Rex-1, which was chosen for further functional analysis. RNAi knockdown of Zfp42 induced ES cells differentiate to endoderm and mesoderm lineages, and overexpression of Zfp42 also caused ES cells to lose the capacity of self-renewal. Our results indicate that RNAi screen is a feasible and efficient approach to identify genes involved in ES cells self-renewal. Further functional characterization of these genes will promote our understanding of the complex regulatory networks in ES cells.

Fishes, the biggest and most diverse community in vertebrates are good experimental models for studies of cell and developmental biology by many favorable characteristics. Nuclear transplantation in fish has been thoroughly studied in China since 1960s. Fish nuclei of embryonic cells from different genera were transplanted into enucleated eggs generating nucleo-cytoplasmic hybrids of adults. Most importantly, nuclei of cultured goldfish kidney cells had been reprogrammed in enucleated eggs to support embryogenesis and ontogenesis of a fertile fish. This was the first case of cloned fish with somatic cells. Based on the technique of microinjection, recombinant MThGH gene has been transferred into fish eggs and the first batch of transgenic fish were produced in 1984. The behavior of foreign gene was characterized and the onset of the foreign gene replication occurred between the blastula to gastrula stages and random integration mainly occurred at later stages of embryogenesis. This eventually led to the transgenic mosaicism. The MThGHtransferred common carp enhanced growth rate by 2-4 times in the founder juveniles and doubled the body weight in the adults. The transgenic common carp were more efficient in utilizing dietary protein than the controls. An all-fish gene construct CAgcGH has been made by splicing the common carp -actin gene (CA) promoter onto the grass carp growth hormone gene (gcGH)