How are gene expression,cellular differation, and cell specialization related?

well, non specialised cells are called stem cells, i think the link is that before gene expression, the cells are totipotent stem cells (have the potential to become any cell), the expression of specific genes in the cell can cause it to differentiate into more specific types of cells, such as cells of the nervous or immune systems which are considered multipotent stem cells, they then can differentiate into pluripotent stem cells (with less of a variety of cells which it can become), the cell will end up specialising into a specific cell such as neurone or b lymphocyte
hope this helps

Gene expression is what causes cells to differentiate and become specialised, and it is the regulation of expression that causes some cells to become nerve cells while others to become muscle cells. Signalling from outside the cell follows a signal pathway into the cell causing operons to be expressed (gene expression) which causes certain proteins to be made which make the cell a certain type (cell differentiation) and these proteins allow the cell to perform certain tasks others cannot (cell specialisation)