Résumé
Locus control regions (LCR) were first defined by their theoretical ability to enhance the expression of linked genes in a tissue-specific, position-independent and copy-number dependent manner. In fact, few of the so-called LCR identified completely fulfil this definition. For example, the regulatory elements located in 5′ (Eμ) and 3′ (HS3a; HS1,2; HS3b; HS4) of the IgH locus display some properties of a LCR but lack a copy-number dependence and sometimes display position effects in transgenes. In order to study whether addition of insulators would allow to overcome such problems in transgenes, we studied constructs harboring a V
H promoter-green fluorescent protein reporter gene linked to the 3′ and/or 5′ IgH elements, surrounded or not with the chicken β-globin 5′HS4 insulator. When flanked with insulators it appeared that either 3′ IgH and 5′ IgH regulatory elements now behave as true LCR elements and noticeably display copy-number dependence in transfected pre-B or B cell lines.