Biotechnology and Bioinformatics (1+1)

4.2.7. Nucleus transplantation

Studies on nucleus transplantation in fishes were initiated in the early 1960's in China.

Tong et al. (1963) first demonstrated the technique, to study the interrelationship between the cell nucleus and cytoplasm . The nucleus of a crucian carp egg was removed with a glass microneedle after removing the egg capsule with forceps, and put into Holtfreter's solution in an ice bath. Then nuclei from the middle or late blastula stage of the common carp were transplanted into the enucleated, unfertilized crucian carp eggs.

In 1973, Tong and Niu, transplanted nuclei between gold fish (Carassius auratus) and Rhodeus sinensis for the purpose of studying the developmental variations between the integrated nuclei and the pure heterologous nuclei, and the effects of cytoplasm on the nucleus. They concluded that character expression (or gene tic expression) was not completely controlled by the nucleus, or by the cytoplasm. In fact, it resulted from interactions between both nucleus and cytoplasm.

Nuclear-cytoplasmic hybrid fishes have been obtained from the combination of nucleus and cytoplasm between two intergeneric species of freshwater teleost using the technique of electric fusion, i.e. the combination of the nucleus of carp (Cyprinus carpio red variety) and the cytoplasm of crucian carp (Carassius auratus red variety).

Morphological characteristics of those hybrid fish that have been examined sofar are similar to those of donor nucleus parental species. Some of the hybrid fish grow to normal adults. The F₃, F₄, F₅ descendents have been spread for farm culture. Protein content of nucleo-cytoplasmic hybrid is 3.78% higher. Fat content 5.88% lower and the growth rate 15-23 percent faster than those of its parents.

Chen et al. (1986) transplanted cell nuclei from a grass carp blastula cell line into unfertilized, enucleated eggs of crucian carp, thus creating the first " test-tube fish". They also obtained two fish by transplanting crucian carp kidney cell nuclei into enucleated crucian carp eggs, and another three fish by transplanting gold fish kidney cell nuclei into enucleated crucian carp eggs as well. These fish grow to reach sexual maturity.

Mao Shujian et al. (1990) transplanted cell nuclei of the mutant cell line (AHZC- 88), which was resistant to the grass carp hemorrhagic virus, into unfertilized grass carp eggs using electric fusion, and raised three of the fish to the fry stage.

These examples demonstrate that fish somatic cells have developmental totipotency . It shows that many different types of cells have the ability to develop to the fry stage, and some have continued to sexual maturity. Thus, there is a possibility of selecting disease resistant or cold resistant cell lines for donors and developing a good strain through nuclear transplantation. More basic work in the area has been done around breeding of virus resistant fishes. Virus-resistant cells have been injected into the eggs of grass carp, loach and white crucian carp, and a few eggs have developed to embryos or fry stage.