1. Cloning animal embryos by nuclear transfer. Under the guidance of Professor An Min from Beijing Agricultural University, he completed his doctoral thesis on cloning rabbit embryos by nuclear transfer in 1993. Later, he worked in many fields, such as nuclear-cytoplasmic interaction in nuclear transplantation, cell cycle synchronization of donors and recipients, and improving the technical efficiency of nuclear transplantation. As early as 1995, in the exploratory experiment of cloning pig embryos by nuclear transfer of primordial germ cells (PGC), the nuclear rearrangement changes after nuclear transfer were found. In sheep cloning, cloned embryo sheep offspring are obtained by synchronizing the cell cycle at division stage (M) and by using eggs matured in vitro. These two techniques are the first in the world, and the in vitro matured eggs are taken from the ovaries of slaughterhouses as by-products, so they are widely available and have great practical application value.
2. Parthenogenetic activation of eggs. Under normal circumstances, eggs are activated by sperm to produce embryonic development. But parthenogenetic activation of eggs is one of the key steps of cloning technology. Only when the eggs are fully activated can cloned embryos be developed after nuclear transfer. Egg activation is not only crucial to cloning efficiency, but also of great significance to the study of early development mechanism and gene imprinting. At Cornell University and the University of Connecticut, Liu Ling has done a lot of work to improve the parthenogenetic activation ability and molecular biological mechanism of eggs, and successfully obtained parthenogenetic activated bovine egg embryos through chemical merger. The development before implantation is equivalent to the activation of sperm fertilization, and the changes of some key kinases are similar. These methods have been widely used in cloning experiments and nuclear transplantation of large animals.
3. Reproductive medicine. How to identify the health status of eggs by non-invasive methods for clinical in vitro fertilization and production of healthy test-tube babies has always been a difficult problem in reproductive medicine. For the first time in the world, the laboratory used a new microscope Polscope to observe and study the spindle of living eggs, thus avoiding the invasive traditional method of fixing the spindle with chemicals and then observing the meiosis spindle and chromosome arrangement of eggs by immunostaining. This new method is gradually moving towards clinical application. This technology has been patented. Liu Ling and his colleagues explored the apoptosis mechanism of aging eggs and embryos in the laboratory, and found that mitochondria were involved in the regulation of egg and embryo apoptosis. It is found for the first time that mitochondria are involved in the regulation of intracellular Ca2+ signal during early development to control embryonic development or apoptosis. They also used a special premature aging mouse model and a telomerase gene deletion mouse model. Recently, it has been reported that the mechanism of infertility in these mice is caused by abnormal chromosome arrangement and spindle structure changes in the metaphase of meiosis. This has a positive effect on understanding human aging and infertility.