ABSTRACT
The use of transgenic mice is invaluable to fulfil the goal; indeed, transgene expression can be studied in all cell types and at any desired time, in the context of developing organism where all the possible regulatory circuits are at work. Different versions of a gene may be used to generate transgenic mice, thereby permitting to map the functional regions of gene implicated in its correct regulation. In summary, the use of transgenic mice has permitted to uncover numerous regulatory elements which act in concert to control the proper expression of Hox genes during mouse embryonic development. These observations in turn raise the important question of transacting factors interacting with these elements and therefore of upstream regulatory genes controlling Hox gene expression. The transgenic methodology has been instrumental in such important aspects of study of development as gene regulation in vivo, search of new genes of developmental importance and the analysis of their function in the various and complex processes.
