**4.2 Somatic cell drying for SCNT**

In tissue banking, as in the banking of germ cells and embryos, storage and maintenance costs are always an issue because of the properties of liquid nitrogen. Seeds of plants, having low water content are relatively easy to preserve at high subzero temperatures (-20 to -30ºC). With water content of about 80%, preservation of gametes and embryos in the animal kingdom is complicated and species-specific. The use of large quantities of liquid nitrogen for cryopreservation and storage also has its toll on the environment, as the production of liquid nitrogen is energy-intensive, resulting in the release of large quantities of carbon dioxide. An alternative to cryopreservation of somatic cells, then, can be to dry them and store the dry cells at room temperature. While, as was discussed earlier, sperm drying has been achieved in a number of species, the parallel in females, namely oocyte drying, is yet to be demonstrated. Somatic cell drying is thus the way to go when long-term storage for females or of the entire genetic complement is desired. In this respect, the use of sheep freeze-dried somatic cells for SCNT was recently demonstrated (Loi et al., 2008a; Loi et al., 2008b). In their report, utilizing the directional freezing technology, freeze-dried granulosa cells, kept at room temperature for 3 years, were used to direct embryonic development following nuclear transfer into *in vitro* matured enucleated oocytes. The reconstructed oocytes initiated cleavage at similar rates to control embryos generated using fresh granulosa cells. Microsatellite DNA analysis of the cloned blastocysts matched perfectly with the lyophilized donor cells. Later, these results were confirmed by other researchers studying mouse granulosa cells (Ono et al., 2008), human hematopoietic stem and progenitor cells (Buchanan et al., 2010) or porcine fetal fibroblasts (Das et al., 2010). These studies demonstrate for the first time that dry cells maintain the development potential when injected into enucleated oocytes. Naturally, we still have a long way to go before live offspring will be generated using this technology but the potential is there.
