It is becoming increasingly accepted that gene loci comprise an extensive c
is-regulatory system that encodes different layers of regulatory informatio
n, all of which are necessary to achieve and maintain tissue-specific gene
expression in ontogeny. To gain a detailed understanding of developmental p
rocesses, it is clearly necessary to unravel the molecular basis behind the
different regulatory processes that control gene expression. This informat
ion is also of utmost importance for any practical application that uses ge
ne transfer technology.