S. Carson et Mv. Wiles, FAR UPSTREAM REGIONS OF CLASS-II MHC EA ARE NECESSARY FOR POSITION-INDEPENDENT, COPY-DEPENDENT EXPRESSION OF EA TRANSGENE, Nucleic acids research, 21(9), 1993, pp. 2065-2072
The chromatin upstream of the class II MHC Ea gene contains specific,
DNase I hypersensitive (DH) sites (groups I - V), overlapping and exte
nding the promoter proximal and distal control regions. To determine w
hether the Ea DH groups I - V define a functionally important chromati
n domain or locus control region (LCR), we have used wild type Ea(d) g
ene constructs to generate transgenic mouse lines from strains that do
not express an endogenous Ea(d) gene product. Constructs contained ei
ther DH groups I - V 'Longs' or DH groups I - II 'Shorts', of the hype
rsensitive sites defined within 20 kb 5' of Ea. We show that position-
independent, copy number-dependent expression of the Ea(d) gene occurs
only with the Long construct (8/8 transgenic mouse lines, over a rang
e of copy numbers, 1 - 30 copies); in contrast, the Short constructs a
re subject to position-dependent effects. This suggests that the regio
n delineated by Ea DH groups I-II is necessary but not sufficient as a
n LCR, which requires the presence of the upstream regions containing
DH III - V for complete position-independent, copy number-dependent ex
pression. These results introduce an immunologically-important, putati
ve LCR which can be used to target genes to cells of the B cell lineag
e, as well as to other class II MHC expressing cells, and highlight th
e importance of chromatin structure analysis as a means to locate DNA
regions of regulatory interest which are dispersed over a large distan
ce.