Insight into "nuclear-cytoplasmic shuttling" as a developmental and differentiational capability of cells in primary culture models.

Shuttling proteins are molecules that can facilitate transport through the nuclear envelope. A very large number of proteins are involved in this process that includes nuclear pore buildup, signal, receptor and enzyme proteins. There are many examples of proteins whose biological activity depends on nucleocytoplasmic transport. Very often they are largely responsible for the proper occurrence of cell division, maturation, development and differentiation. Thanks to the well mastered methods of in vitro cell culture, it is possible to trace the levels of protein expression and their distribution in cells. Advanced molecular techniques allow for precise determination of their displacement in time. Several studies are still being carried out, using primary cultures, to identify the factors that determine the maturation, development and differentiation of cells. In understanding of the detailed mechanisms controlling cell life, the key is not the level of expression of a specific protein, but its distribution in individual cellular compartments.