Polymorphisms and DNA methylation: two ways for functional differences in the 3' regulatory region of the IgH locus
2007
The IgH locus in mouse and human has a 3' regulatory region (3'RR)
with multiple DNaseI hypersensitive sites. In the human, but not in the
mouse, the sites (HS3, HS1.2 and HS4) are duplicated. One unit is
downstream of the Cα-1 gene and a second unit is downstream of the Cα-2
gene. Human HS1,2 enhancers show polymorphic features.
In the mouse, HS3A, HS1.2, HS3B and HS4 are enhancers involved in
the expression and class switching of immunoglobulin heavy chain genes.
A recently identified downstream region, which contains hypersensitive
sites HS5, HS6 and HS7, has been hypothesized to serve as an insulator of
the Igh locus. This downstream region is associated with marks of active
chromatin throughout B cell development and contains binding sites for
CTCF, a protein associated with mammalian insulators. CTCF binding to
many of its cognate DNA sites is prevented by DNA methylation. Previous
studies using genomic Southern analysis have shown changes in DNA
methylation in the upstream region of the murine 3' RR during B cell
development.
In the first part of this work I identified the polymorphic structure of
human HS1,2, and its distribution in some populations and in some
immunological diseases. The data suggest that the HS1,2 enhancer that lies
downstream of the Cα-1 gene has four alleles, one of which, allele *2, is
more frequent in some immunological disorders and less frequent in the
sub-Saharan region. I have also observed using EMSA that protein binding
is different in the four alleles.
Furthermore I have studied changes in DNA methylation in the murine
3'RR during B cell development by digesting genomic DNA with
methylation-sensitive restriction enzymes, such as HpaII and MaeII,
followed by PCR. The data revealed that the 3’RR is methylated in
embryonic stem cells. ES cells derived from histone H1 depleted mice
showed a reduction in methylation as compared to their respective wildtype
counterparts. I have detected a progressive loss of DNA methylation
during B cell development. DNase I HS sites HS4, HS5 and HS7 are the
earliest regulated and unmethylated sites in cell lines reflecting early stages
of B development, while the HS1.2 and HS3B enhancers are unmethylated
3
only in plasma cell lines. DNA methylation is also reduced in splenic
Keywords:
- Correction
- Cite
- Save
- Machine Reading By IdeaReader
94
References
0
Citations
NaN
KQI