Journal of Neuroscience, Vol 15, 3342-3356, Copyright © 1995 by Society for Neuroscience
Elements in the 5' flanking sequences of the mouse low-affinity NGF receptor gene direct appropriate CNS, but not PNS, expression in transgenic mice
SL Carroll, JB Schweitzer, DM Holtzman, ML Miller, GM Sclar and J Milbrandt
Department of Pathology, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
We have initiated a characterization of the cis-acting regulatory elements
of the murine low-affinity NGF receptor (p75NGFR) gene. Despite studies in
cultured cells that suggest the p75NGFR promoter is constitutive, a
detailed analysis of this promoter in five lines of transgenic mice
demonstrated a high degree of cell-type specificity: 8.4 kb of 5' flanking
sequence directs expression of a lacZ reporter to retinal and CNS neurons
normally expressing p75NGFR. A transgene with 470 bp of 5' flanking
sequence is also expressed in the CNS, but its regulation is aberrant, with
a loss of basal forebrain expression. In non-neural tissues, both
transgenes were expressed only in the testis, kidney, anterior pituitary,
and pancreatic islets; with the exception of the renal pattern of
expression, transgene activity was confined to appropriate cells within
these tissues. In contrast, although expression of both transgenes was
prominent in adrenal medulla and gastrointestinal myenteric neurons,
neither construct was active in several sensory or sympathetic ganglia that
strongly express the endogenous p75NGFR gene, indicating that genetic
elements necessary for expression in these neurons are not present in these
promoter sequences. In addition, neither transgene was activated in Schwann
cells during Wallerian degeneration of sciatic nerve. We conclude that
regulation of the p75NGFR gene is complex, with the first 470 bp of 5'
flanking sequence sufficient for expression in enteric and CNS neurons and
additional elements within the first 8.4 kb of 5' flanking sequence
required for restriction to appropriate CNS neurons. Further regulatory
elements are possibly required for expression in at least some sensory and
sympathetic neurons in the PNS and in Schwann cells. To identify potential
regulatory elements in the 470 bp of 5' flanking sequence from the smaller
transgene, we compared the sequences of equivalent regions from the mouse,
rat, and human p75NGFR genes. This "phylogenetic footprint" identified
conserved motifs potentially important for the regulation of this gene in
the CNS.