AN OVERVIEW OF TRANSGENIC ANIMALS USING SPECIALISED STEM CELLS.
Found in the mammalian testis, Spermatogonial stem cells (SSCs) have the ability to multiply (produce millions of sperms in one day) and are a group of cells in the seminiferous tubules with tremendous self-renewal potential. Because of their renewing capacity, it provides as an omnipotent support for spermatogenesis in a male animal for life. With these pluripotent characteristics, researchers claim SSCs to be appropriate for genetic manipulation in the field for transgenic animals. The first successful SSC transplantation in mice was in 1994 by Brinster and his colleagues, and since then, it's become one of the top notch researching topics.
THE SOURCE AND FORMATION OF THE SSCs.
Primordial germ cells (PGCs, also known as precursor germ cells) are germ cells that divide continuously through their migratory route to the gonads. The SSCs are basically adult stem cells derived from those PGCs. In males, they become spermatocytes (surrounded by supporting cells) upon entering the seminiferous tubules of the fetal testis. A portion of these spermatocytes acquire flagella, move to the basement membrane where they settle n the seminiferous tubule-based membrane. Here they become embedded in the supporting cells and differentiate into SSCs. Within the females, the PGCs become oocytes after meiosis, thus losing their stem cell potential.
SSCs IN TRANSGENIC ANIMALS.
SSC divides rapidly within all male mammals. If an SSC chromosome is integrated with exogenous DNA, there is a possibility that the sperm might carry the foreign gene. Since the SSC has a duplicating ability and of sustaining itself within the male, this gene will be retained for long within the stem cells. Its precisely this ability that makes SSC so advantageous for the transgenic animals. To date, seminiferous tubule injected and transplantation of spermatogonial stems cells are the major methods to transfer SSC based production of transgenic animals.
SSCs IN DOMESTIC LIVESTOCK.
Transgenic animals have better genetic merits due to the improved breeding efficiency which increases the economic value of the livestock. It allows the breeding of animals in extreme climates, resulting in valuable offspring. Using SSCs for livestock transgenises has its own set of advantages. The methods involved within might reduce the time to collect transgenic sperm by one generation, as compared to the current methods. This in turn will help in cutting costs, and tremendous growth in the generation for large scale production.
CONCLUSIONS : LIMITATATIONS AND PROSPECTS
As a process, it is easier using SSCs since there's no inclusion of specialized equipment. Even then, SSCs transgenesis definitely has its drawbacks. Injecting seminiferous tubules is simple, but the probability that a SSC is transfected is low in the testis, therefore fewer chances of the offspring being transgenic. SSC's transgenises technology involves methods such the isolation, purification, in vitro culture and preservation. Very few animals at present, can produce transgenic offsprings through these methods.
To conclude, the SSCs (as we have seen) have highly appropriate features in order to produce transgenic animals that could have a significant impact in the breeding of livestock. Future research might help in eliminating the limitations, providing the acceleration for the growth of transgenic offsprings.
Honaramooz A, Yang Y. 2011. Recent advances in application
of male germ cell transplantation in farm animals. Veterinary
Medicine International, Article ID 657860, doi:10.4061/2011/
MIAO X. Agricultural Sciences in China
2011, 10(5): 762-768.