Long-distance chromatin mechanisms controlling tissue-specific gene locus activation

Several different types of regulatory mechanisms contribute to the tissue- and development-specific regulation of a gene. It is now well established t hat, in addition to promoters, upstream cis-regulatory elements, which bind a variety of trans-acting factors, are essential for correct gene activati on. In the last few years, however, it has become evident that the chromati n structure of eukaryotic genes is an important additional regulatory layer that is essential for correct gene expression during development. Chromati n is essentially a repressive environment for transcription factors; hence, much effort in recent years has been devoted to the elucidation of how the se repressive forces are overcome during the process of gene locus activati on. A particular interesting question in this context is: what are the mole cular mechanisms by which extensive regions of chromatin, in many cases far outside the coding region, are reorganized during development? In this rev iew, I summarize data from recent investigations that have uncovered a surp rising variety of factors involved in this process. (C) 1999 Elsevier Scien ce B.V. All rights reserved.