Journal of Neuroscience, Vol 10, 2850-2860, Copyright © 1990 by Society for Neuroscience
Carboxypeptidase E (enkephalin convertase): mRNA distribution in rat brain by in situ hybridization
MW MacCumber, SH Snyder and CA Ross
Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205.
Carboxypeptidase E (CPE), also referred to as enkephalin convertase or
carboxypeptidase H (EC 3.4.17.10), is present in neurotransmitter secretory
granules and can remove C-terminal basic residues following endopeptidase
cleavage during peptide processing. Using in situ hybridization with
35S-labeled oligonucleotide probes, we have mapped the localization of CPE
mRNA in the rat brain. Specificity for CPE was confirmed by control
experiments, which included production of identical patterns hybridization
with 3 different antisense oligonucleotide probes, loss of label with RNase
pretreatment of sections or co-incubation with excess unlabeled probe, and
lack of labeling with sense orientation probes. In addition, the regional
distribution of CPE mRNA by Northern blot analysis corresponded with
distribution of labeling by in situ hybridization. The highest levels of
CPE mRNA were found to be present in the pyramidal cells of the
hippocampus, the pituitary anterior and intermediate lobes, the ependymal
cells of the lateral ventricle, the endopiriform nucleus, the basolateral
amygdala, the supraoptic nucleus, and the paraventricular nucleus.
Intermediate levels were present in the thalamus, medial geniculate
nucleus, lateral septal nucleus, piriform and entorhinal cortex, nucleus of
the tractus solitarius, cerebellar cortex, pontine nuclei, and inferior
olive. The lowest levels were found in the hippocampal granule cell layer,
lateral hypothalamus, globus pallidus, and brain stem reticular formation.
Ibotenic acid lesions of the hippocampus eliminated the majority of the
label, which had been present over pyramidal cells, though labeling was
increased over areas of reactive gliosis, suggesting that activated
astrocytes can also synthesize CPE mRNA. In general, the localization of
CPE mRNA in the rat brain corresponded to the distribution of enkephalin
and other peptide neurotransmitter-synthesizing neurons, though CPE mRNA
was also present in neurons that do not secrete known peptides and in
reactive glia. The widespread yet specific localization of CPE mRNA in the
rat brain suggests it may be an excellent marker for peptide synthesizing
cells in the CNS.