1: J Biol Chem. 1995 Sep 8;270(36):21291-8. 

Silencer elements modulate the expression of the gene for the neuron-glia cell
adhesion molecule, Ng-CAM.

Kallunki P, Jenkinson S, Edelman GM, Jones FS.

Department of Neurobiology, Scripps Research Institute, La Jolla, California
92037, USA.

The combined factors that regulate the expression of cell adhesion molecules
(CAMs) during development of the nervous system are largely unknown. To identify
such factors for Ng-CAM, the neuron-glia CAM, constructs containing portions of
the 5' end of the Ng-CAM gene were examined for activity after transfection into
N2A neuroblastoma and NIH3T3 cells. Positive regulatory elements active in both
cell types included an Ng-CAM proximal promoter with SP1 and cAMP response
element motifs extending 447 base pairs upstream of a single RNA start site and
a region within the first exon corresponding to 5'-untranslated sequences.
Negative regulatory elements included five neuron-restrictive silencer elements
(NRSEs) and a binding site for Pax gene products in a 305-base pair segment of
the first intron. Constructs containing the promoter together with the entire
first intron were active in N2A cells but were silenced in NIH3T3 cells. This
silencer activity was mapped to the NRSEs. In contrast, the Pax motif inhibited
activity of Ng-CAM constructs in both cell types. The DNA elements defined in
these transfection experiments were examined for their ability to bind nuclear
factors. The region within the first exon formed a DNA-protein complex after
exposure to nuclear extracts prepared from both NIH3T3 and N2A cells. The NRSE
region formed a more prominent complex with proteins prepared from NIH3T3 cells
than it did with extracts from N2A cells. A member of the Pax protein family,
Pax-3 bound to the Pax motif. Mutations introduced within the Pax motif in its
ATTA sequence eliminated this binding whereas mutations in its GTTCC sequence
did not, suggesting that paired homeodomain interactions are important for the
recognition of Pax-3 by this DNA target sequence. The combined data suggest that
negative regulation by NRSEs and Pax proteins may play a key role in the
place-dependent expression patterns of Ng-CAM during development.

PMID: 7545667 [PubMed - indexed for MEDLINE]


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